DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.

NONRESIDENT

TRAININGCOURSE

July 1997

Electronics Technician

Volume 3—CommunicationsSystems

NAVEDTRA 14088

DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.

Although the words “he,” “him,” and“his” are used sparingly in this course toenhance communication, they are notintended to be gender driven or to affront ordiscriminate against anyone.

i

PREFACE

By enrolling in this self-study course, you have demonstrated a desire to improve yourself and the Navy.Remember, however, this self-study course is only one part of the total Navy training program. Practicalexperience, schools, selected reading, and your desire to succeed are also necessary to successfully roundout a fully meaningful training program.

COURSE OVERVIEW: After completing this course, you should be able to: recall the basic principleand the basic equipment used for rf communications; recognize frequency bands assigned to the Navymicrowave communications, the single audio system (SAS), and the basics of the Navy tactical data system.Analyze the operation of the Navy’s teletypewriter and facsimile system, the basics of the TEMPESTprogram, and the basic portable and pack radio equipment used by the Navy. Identify basic satellitecommunications fundamentals, fleet SATCOM subsystem, shore terminals, and basic SATCOM equipmentand racks. Identify the composition of the Link-11 system, and problems in Link-11 communications.Recognize the functions of the Link 4-A systems, new technology in data communications, and local-areanetworks.

THE COURSE: This self-study course is organized into subject matter areas, each containing learningobjectives to help you determine what you should learn along with text and illustrations to help youunderstand the information. The subject matter reflects day-to-day requirements and experiences ofpersonnel in the rating or skill area. It also reflects guidance provided by Enlisted Community Managers(ECMs) and other senior personnel, technical references, instructions, etc., and either the occupational ornaval standards, which are listed in the Manual of Navy Enlisted Manpower Personnel Classificationsand Occupational Standards, NAVPERS 18068.

THE QUESTIONS: The questions that appear in this course are designed to help you understand thematerial in the text.

VALUE: In completing this course, you will improve your military and professional knowledge.Importantly, it can also help you study for the Navy-wide advancement in rate examination. If you arestudying and discover a reference in the text to another publication for further information, look it up.

1997 Edition Prepared byDSCS(SW/AW) Robert M. Maynard

Published byNAVAL EDUCATION AND TRAINING

PROFESSIONAL DEVELOPMENTAND TECHNOLOGY CENTER

NAVSUP Logistics Tracking Number0504-LP-026-7540

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Sailor’s Creed

“I am a United States Sailor.

I will support and defend theConstitution of the United States ofAmerica and I will obey the ordersof those appointed over me.

I represent the fighting spirit of theNavy and those who have gonebefore me to defend freedom anddemocracy around the world.

I proudly serve my country’s Navycombat team with honor, courageand commitment.

I am committed to excellence andthe fair treatment of all.”

CONTENTS

CHAPTER PAGE

1. Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

2. Systems Equipment Configurations . . . . . . . . . . . . . . . . . 2-1

3. Satellite Communications . . . . . . . . . . . . . . . . . . . . . 3-1

4. The Link-11 System . . . . . . . . . . . . . . . . . . . . 4-1

5. Link-11 Fault Isolation . . . . . . . . . . . . . . . . . . . . . . . . 5-1

6. Link-4A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

7. New Technology in Data Communications . . . . . . . . . . . . . 7-1

8. Local-Area Networks . . . . . . . . . . . . . . . . . . . . . . . . 8-1

APPENDIX

I. List of Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .AI-1

II. References Used To Develop The TRAMAN. . . . . . . . . . . AII-1

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INDEX-1

NONRESIDENT TRAINING COURSE follows the index

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SUMMARY OF THEELECTRONICS TECHNICIAN

TRAINING SERIES

This series of training manuals was developed to replace the ElectronicsTechnician 3 & 2 TRAMAN.

The nine volumes in the series are based on major topic areas with which theElectronics Technician should be familiar. Volume 1, Safety, provides anintroduction to general safety as it relates to the ET rating. It also provides bothgeneral and specific information on electronic tag-out procedures, man-aloftprocedures, hazardous materials (i.e., solvents, batteries, and vacuum tubes), andradiation hazards. Volume 2, Administration, discusses COSAL updates, 3-Mdocumentation, supply paperwork, and other associated administrative topics.Volume 3, Communications Systems, provides a basic introduction to shipboard andshore-based communication systems. Systems covered include man-pac radios(i.e., PRC-104, PSC-3) in the hf, vhf, uhf, SATCOM, and shf ranges. Also providedis an introduction to the Communications Link Interoperability System (CLIPS).Volume 4, Radar Systems, is a basic introduction to air search, surface search,ground controlled approach, and carrier controlled approach radar systems. Volume5, Navigation Systems, is a basic introduction to navigation systems, such asOMEGA, SATNAV, TACAN, and man-pac systems. Volume 6, Digital DataSystems, is a basic introduction to digital data systems and includes discussionsabout SNAP II, laptop computers, and desktop computers. Volume 7, Antennas andWave Propagation, is an introduction to wave propagation, as it pertains toElectronics Technicians, and shipboard and shore-based antennas. Volume 8,Support Systems, discusses system interfaces, troubleshooting, sub-systems, dry air,cooling, and power systems. Volume 9, Electro-Optics, is an introduction to nightvision equipment, lasers, thermal imaging, and fiber optics.

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v

INSTRUCTIONS FOR TAKING THE COURSE

ASSIGNMENTS

The text pages that you are to study are listed atthe beginning of each assignment. Study thesepages carefully before attempting to answer thequestions. Pay close attention to tables andillustrations and read the learning objectives.The learning objectives state what you should beable to do after studying the material. Answeringthe questions correctly helps you accomplish theobjectives.

SELECTING YOUR ANSWERS

Read each question carefully, then select theBEST answer. You may refer freely to the text.The answers must be the result of your ownwork and decisions. You are prohibited fromreferring to or copying the answers of others andfrom giving answers to anyone else taking thecourse.

SUBMITTING YOUR ASSIGNMENTS

To have your assignments graded, you must beenrolled in the course with the NonresidentTraining Course Administration Branch at theNaval Education and Training ProfessionalDevelopment and Technology Center(NETPDTC). Following enrollment, there aretwo ways of having your assignments graded:(1) use the Internet to submit your assignmentsas you complete them, or (2) send all theassignments at one time by mail to NETPDTC.

Grading on the Internet: Advantages toInternet grading are:

• you may submit your answers as soon asyou complete an assignment, and

• you get your results faster; usually by thenext working day (approximately 24 hours).

In addition to receiving grade results for eachassignment, you will receive course completionconfirmation once you have completed all the

assignments. To submit your assignmentanswers via the Internet, go to:

https://courses.cnet.navy.mil

Grading by Mail: When you submit answersheets by mail, send all of your assignments atone time. Do NOT submit individual answersheets for grading. Mail all of your assignmentsin an envelope, which you either provideyourself or obtain from your nearest EducationalServices Officer (ESO). Submit answer sheetsto:

COMMANDING OFFICERNETPDTC N3316490 SAUFLEY FIELD ROADPENSACOLA FL 32559-5000

Answer Sheets: All courses include one“scannable” answer sheet for each assignment.These answer sheets are preprinted with yourSSN, name, assignment number, and coursenumber. Explanations for completing the answersheets are on the answer sheet.

Do not use answer sheet reproductions: Useonly the original answer sheets that weprovide—reproductions will not work with ourscanning equipment and cannot be processed.

Follow the instructions for marking youranswers on the answer sheet. Be sure that blocks1, 2, and 3 are filled in correctly. Thisinformation is necessary for your course to beproperly processed and for you to receive creditfor your work.

COMPLETION TIME

Courses must be completed within 12 monthsfrom the date of enrollment. This includes timerequired to resubmit failed assignments.

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PASS/FAIL ASSIGNMENT PROCEDURES

If your overall course score is 3.2 or higher, youwill pass the course and will not be required toresubmit assignments. Once your assignmentshave been graded you will receive coursecompletion confirmation.

If you receive less than a 3.2 on any assignmentand your overall course score is below 3.2, youwill be given the opportunity to resubmit failedassignments. You may resubmit failedassignments only once. Internet students willreceive notification when they have failed anassignment--they may then resubmit failedassignments on the web site. Internet studentsmay view and print results for failedassignments from the web site. Students whosubmit by mail will receive a failing result letterand a new answer sheet for resubmission of eachfailed assignment.

COMPLETION CONFIRMATION

After successfully completing this course, youwill receive a letter of completion.

ERRATA

Errata are used to correct minor errors or deleteobsolete information in a course. Errata mayalso be used to provide instructions to thestudent. If a course has an errata, it will beincluded as the first page(s) after the front cover.Errata for all courses can be accessed andviewed/downloaded at:

https://www.advancement.cnet.navy.mil

STUDENT FEEDBACK QUESTIONS

We value your suggestions, questions, andcriticisms on our courses. If you would like tocommunicate with us regarding this course, weencourage you, if possible, to use e-mail. If youwrite or fax, please use a copy of the StudentComment form that follows this page.

For subject matter questions:

E-mail: n315.products@cnet.navy.milPhone: Comm: (850) 452-1001, Ext. 1713

DSN: 922-1001, Ext. 1713FAX: (850) 452-1370(Do not fax answer sheets.)

Address: COMMANDING OFFICERNETPDTC N3156490 SAUFLEY FIELD ROADPENSACOLA FL 32509-5237

For enrollment, shipping, grading, orcompletion letter questions

E-mail: fleetservices@cnet.navy.milPhone: Toll Free: 877-264-8583

Comm: (850) 452-1511/1181/1859DSN: 922-1511/1181/1859FAX: (850) 452-1370(Do not fax answer sheets.)

Address: COMMANDING OFFICERNETPDTC N3316490 SAUFLEY FIELD ROADPENSACOLA FL 32559-5000

NAVAL RESERVE RETIREMENT CREDIT

If you are a member of the Naval Reserve, youmay earn retirement points for successfullycompleting this course, if authorized undercurrent directives governing retirement of NavalReserve personnel. For Naval Reserve retire-ment, this course is evaluated at 9 points. (Referto Administrative Procedures for NavalReservists on Inactive Duty, BUPERSINST1001.39, for more information about retirementpoints.)

vii

Student Comments

Course Title: Electronics Technician, Volume 3—Communications Systems

NAVEDTRA: 14088 Date:

We need some information about you:

Rate/Rank and Name: SSN: Command/Unit

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Privacy Act Statement: Under authority of Title 5, USC 301, information regarding your military status isrequested in processing your comments and in preparing a reply. This information will not be divulged withoutwritten authorization to anyone other than those within DOD for official use in determining performance.

NETPDTC 1550/41 (Rev 4-00

CHAPTER 1

FUNDAMENTALS

INTRODUCTION

Communications in general, and especially in systems, covers a broad spectrum, from a simple single-channel voice circuit, to the fastest growing field of electronics—satellite communications. This trainingmanual will provide you with knowledge applicable to questions and situations that arise on the job. Chapter1 is a refresher course in basic communications systems and terminology. Chapters 2 and 3 will lead youthrough many of the systems and equipments in use today. Chapter 4 will discuss the Link-11 system, chapter5 will cover the Link-11 Fault Isolation, chapter 6 will discuss Link 4-A, chapter 7 will introduce you to thenew technology in data communications and the Link-16 system, and chapter 8 will discuss local-areanetworks.

The Electronics Technician rating is extremely diverse. Many ETs never get the opportunity to work inthe communications field. Those who do are often locked into one particular system for many years. Thisassignment pattern sometimes causes ETs to feel overwhelmed or lost in their career. The massive amount ofinformation ETs can be questioned on and expected to know can be frustrating. But the goal YOU and everyET must have is to become as knowledgeable as possible to be better. prepared for all future challenges.

After completing this chapter, you should be able to:

Identify the basic principles of rf communications

Recognize the basic equipment used for rf communications

Determine the frequency spectrum allocated to rf communications

RADIO COMMUNICATIONS

Navy ships, planes, and shore bases operate as ateam working together to accomplish a specific task.Radio equipment is used to coordinate the activities ofthe many fleet units by linking them with each otherand with shore stations.

Radio can be defined as the transmission and re-ception of electronic impulses or signals through spaceby means of electromagnetic waves. Usually, the termis used in referring to the transmission of intelligencecode and sound signals, although television and radaralso depend on electromagnetic waves.

At one time, the term radio communicationsbrought to mind telegraphy (CW), voice (AM), andpossibly teletype communications. Today’s radio com-munications has become a highly sophisticated field ofelectronics. You, the technician, need to become fa-miliar with the diverse systems in use today.

The primary means of communicating betweenships and between ships and stations is known as tele-communications. Telecommunications refers to com-munications over a distance and includes any

transmission, emission, or reception of signals,writing, images, and sounds. Intelligence produced byvisual or oral means or by wire, radio, or other electro-magnetic systems is also included. Electrical, visual,and sound telecommunications are all used by theNavy. In this volume we will discuss electrical types oftelecommunications.

COMMUNICATIONS SYSTEMS

A communications system consists of two or moreunits, each having its own separate identity, arrangedand interconnected to perform a circuit operation thatcannot be performed by one of the individual unitsalone. Navy communications systems vary from sim-ple to very complex, depending upon the circuit opera-tions involved. Each system requires the integrated useof various types of equipment, so flexibility is of the ut-most importance. This flexibility is provided through acomplex arrangement of interconnections that allowthe physically separated sets, groups, and units to beselectively switched (patched) into the different circuitconfigurations.

1-1

Most shipboard communication equipments donot operate independently. A particular piece of elec-tronic gear may be designated “primary” and still beused in many different system operations. You need tounderstand all the associated equipment in a system toidentify problems correctly and to make repairspromptly. Thorough knowledge of system operationswill enable you to say with complete confidence, thiscommunications suite is operational.

SAFETY

Hazards encountered in servicing electronicequipment and the precautions to be taken againstthem are covered thoroughly in Electronics Techni-cian Volume 1, Safety, NAVEDTRA 12411, and theGeneral Handbook (NAVSHIPS 0967-000-0100) ofthe EIMB series.

Safety is everyone’s responsibility. Observance ofsafety precautions will keep your equipment operat-ing, help your career in the Navy, and possibly deter-mine whether or not you survive. Always follow theappropriate safety precautions!

Note: Equipment that we cover in this andother chapters is intended to be merely repre-sentative of equipment that you may encounteron board your command. We will not attempt toinclude all the possible equipment or equipmentconfigurations.

BASIC SYSTEM REQUIREMENTS

Radio equipment can be divided into threebroad categories: transmitting equipment, receivingequipment, and terminal equipment. Transmitting

Figure 1-1.—Basic radio communication system.

equipment generates, amplifies, and modulates atransmitted signal. Receiving equipment receives aradio wave, then amplifies and demodulates it to extractthe original intelligence. Terminal equipment is usedprimarily to convert the audio signals of encoded or datatransmission into the original intelligence.

A basic radio communications system may consistof only a transmitter and a receiver, connected by themedium through which the electromagnetic wavestravel (see figure 1-1). The transmitting equipmentcreates a radio-frequency (rf) carrier and modulates itwith audio intelligence to produce an rf signal. This rfsignal is amplified and fed to the transmitting antenna,which converts it to electromagnetic energy for propa-gation.

The receiving antenna converts the portion of theelectromagnetic wave it receives into a flow of alter-nating rf currents. The receiver then converts thesecurrents into the intelligence that was contained in thetransmission.

Terminal equipment is used primarily wherecoded transmissions are employed, to convert themodulated signal into the original intelligence. Sys-tems you will encounter in the fleet use terminal equip-ment, such as AN/UCC-l, AN/URA-17, and CV-2460.

THE FREQUENCY SPECTRUM

Figure 1-2 shows the overall electromagnetic fre-quency spectrum as defined by the International Tele-communications Union. Pay particular attention to thepart used for communications. Rapid growth in thequantity and complexity of communications equip-ment and increased worldwide international require-ments for radio frequencies have placed large demandsupon the rf spectrum. These demands include militaryand civilian applications, such as communications, lo-cation and ranging, identification, standard time, in-dustrial, medical, and other scientific uses.

The military has modified the frequency spectrumfor its use as shown in table 1-1. A few general charac-teristics are described in the following paragraphs.

The extremely-low-frequency (elf), very-low-frequency (vlf), and low-frequency (lf) bands requirehigh power and long antennas for efficient transmis-sion (antenna length varies inversely with the fre-quency). Transmission of these frequencies isnormally limited to shore stations.

The commercial broadcast band extends fromabout 550 kHz to 1700 kHz. This limits naval use to the

1-2

Table 1-1.—Frequency Bands.

upper and lower ends of the medium frequency (mf)band.

Long-range shipboard communications were con-ducted exclusively in the high-frequency (hf) band, soa large percentage of shipboard transmitters and re-ceivers are designed to operate in this band. On boardyour command, you may find satellite communica-tions has pushed hf into aback-up role.

A significant portion of the very-high-frequency(vhf) band is assigned to the commercial television in-dustry. Some naval uses of the vhf band are mobile

communications, repeater operation, navigation, am-phibious and special operations, short range line-of-sight (LOS) communications, and satellite communi-cations.

The ultra-high-frequency (uhf) band is used exten-sively by the Navy for LOS and satellite communica-tions. Mobile communications, radar (over 400 MHz),and special operations are some other uses.

The super-high-frequency (shf) band is the work-horse of microwave communications. LOS communi-

Figure 1-2.—Frequency spectrum.

1-3

cations, terrestrial, and satellite relay links, radar, andspecial operations are some other uses.

Experimental use of the extremely-high-frequency (ehf) band is ending. The Fleet Satellite(FLTSAT) Ehf Package (FEP) is attached to twomodified uhf FLTSATs. The FEP is currently provid-ing ehf communications capability to Army, Navy, andAir Force ground, airborne, and oceangoing terminals.We will discuss the FEP and its purpose in chapter 3.

Infrared devices and lasers use even higher fre-quency ranges. Information on equipment using thesefrequencies can be found in Electro-Optics, volume 9,of this training series.

RADIO EMISSIONS

The emission class of an rf transmitter is deter-mined by the type of modulation used. The interna-tional designation system for AM and FM emissions isshown in table 1-2. It designates the rf emission bytype, mode, and supplemental characteristics.

We will now discuss the basic equipment requiredfor communications.

TRANSMITTERS

For rf communications to take place, a signal has tobe generated. Generating the signal is the job of thetransmitter. The following paragraphs will very brieflydiscuss basic transmitters and transmitter fundamen-tals.

TRANSMITTER FUNDAMENTALS

Equipment used for generating, amplifying, andtransmitting an rf carrier is collectively called a radiotransmitter. Transmitters may be simple, low-powerunits, for sending voice messages a short distance orhighly sophisticated, using thousands of watts ofpower for sending many channels of data (voice, tele-type, telemetry, t.v., etc.,) over long distances.

Basic transmitters are identified by their method ofmodulation: continuous wave (CW), amplitude modu-lation (AM), frequency modulation (FM), or single-sideband (ssb). We will first describe the types ofmodulation. We will then describe briefly the basictransmitters themselves.

Table 1-2.—Types of Radio Emissions

MODULATION

Modulation is the process of varying some charac-teristic of a periodic wave with an external signal. Thevoice frequencies (about 110-3,000 Hz) are contained

1-4

in the audio frequency spectrum, 10-20,000 Hz. In na-val communications the terms voice communicationsand audio communications are sometimes used inter-changeably. The audio signal is impressed upon the rfcarrier because it is impractical to transmit frequen-cies in the audio range due to their excessive wave-length.

Three characteristics of the carrier wave may bevaried, or modulated, at an external signal rate: ampli-tude, frequency, and phase. The following paragraphsdiscuss each type of modulation.

Amplitude Modulation (AM)

Amplitude modulations the process of combiningaudio frequency and radio frequency signals so that theamplitude of the radio frequency waves varies at anaudio frequency rate.

Frequency Modulation (FM)

Frequency modulation is a process in which thefrequency of the carrier wave is made to vary. An FMsignal should remain constant in amplitude and change

Frequency-Shift Keying (FSK)

Frequency-shift keying is considered a form ofFM. It is a digital mode of transmission commonlyused in radioteletype applications. In FSK the carrier ispresent all the time. In a keyed condition, the carrierfrequency changes by a predetermined amount called

the mark frequency. The unkeyed state is called aspace.

Phase-Shift Keying (PSK)

Phase-shift keying is similar to FSK except that thephase, not the frequency, is shifted. The primary ad-vantage of PSK is that it can be accomplished in an am-plifier stage.

Pulse Modulation

Pulse modulation is accomplished by varying thecharacteristics of a series of pulses. This can be doneby varying the amplitude, duration, frequency, or posi-tion of the pulses. It can also be done through coding.Pulse modulation is especially suited for use with com-munications systems incorporating time-division mu-tiplexing.

BASIC TRANSMITTERS

Remember, transmitters are generally divided ac-cording to their type of modulation. In the discussionbelow, we describe very briefly how each type oper-ates to help you differentiate between them.

CW Transmitter

A basic CW transmitter is shown in figure 1-3. CWis one of the oldest and least complicated forms ofcommunications. Two advantages of CW are a narrowbandwidth, which requires less power out, and clarity,even under high noise conditions. The major disadvan-

only in frequency.

Figure 1-3.—Continuous-wave transmitter.

1-5

tage of a CW transmitter is that it must be turned on andoff at specific intervals to produce Morse code keying(dots and dashes). This method is very slow by modernday standards. A better method of transmitting is AM.

AM Transmitter

Figure 1-4, a block diagram of an AM transmitter,shows you what a simple AM transmitter looks like.The microphone converts the audio frequency input toelectrical energy. The driver and modulator amplifythe audio signal to the level required to modulate thecarrier fully. The signal is then applied to the poweramplifier (pa). The pa combines the rf carrier and themodulating signal to produce the AM signal for trans-mission.

FM Transmitter

A block diagram of an FM transmitter is shown infigure 1-5. The transmitter oscillator is maintained at aconstant frequency by a quartz crystal. This steady sig-nal is passed through an amplifier, which increases theamplitude of the rf subcarrier. The audio signal is ap-plied to this carrier phase-shift network. Here, the fre-quency of the carrier shifts according to audio signalvariations. The FM output of the phase-shift network is

fed into a series of frequency multipliers that increasethe signal to the desired frequency. The signal is thenamplified in the power amplifier and coupled to the an-tenna.

Two important things to remember are (1) theamount of variation from the carrier frequency de-pends on the magnitude of the modulating signal and(2) the rate of variations in carrier frequency dependson the frequency of the modulating signal.

The FM transmitter is better than an AM transmit-ter for communications purposes because FM is lessaffected by static and other types of interference. Aneven better transmitter is the single-sideband transmit-ter, or ssb. Let’s look at some of the advantages of ssbtransmitters.

SINGLE-SIDEBAND TRANSMITTER

In ssb communications, the carrier is suppressed(eliminated) and the sideband frequencies produced bythe carrier are reduced to a minimum. This means nocarrier is present in the transmitted signal. It is re-moved after the signal is modulated and reinserted atthe receiver during demodulation. Since there is nocarrier, all the energy is concentrated in the side-band(s).

Figure 1-4.—AM transmitter block diagram.

1-6

Figure 1-5.—FM transmitter block diagram.

We can make ssb even more efficient by removingone of the sidebands. By filtering out one of the side-bands before it reaches the power amplifier, all thetransmitter energy is concentrated into one side-band instead of being split between the carrier andtwo sidebands. This allows us to use less power fortransmission. Other advantages are a narrower re-ceiver bandpass and the ability to place more signals ina small portion of the frequency spectrum. Figure 1-6is a block diagram of a ssb transmitter.

RECEIVERS

Earlier you were introduced to one link in a com-munications system, the transmitter. All that is neededto complete the system is a radio receiver. A receiver

processes modulated signals and delivers, as an output,a reproduction of the original intelligence. The signalcan then be applied to a reproducing device, such as aloudspeaker or a teletypewriter.

RECEIVER FUNCTIONS

To be useful, a receiver must perform certain basicfunctions. These functions are reception, selection, de-tection, and reproduction.

Reception

Reception occurs when a transmitted electromag-netic wave passes through the receiver antenna and in-duces a voltage in the antenna.

Figure 1-6.—SSB transmitter block diagram.

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Selection

Selection is the ability to distinguish a particularstation’s frequency from all other station frequenciesappearing at the antenna.

Detection

Detection is the extraction of the modulation froman rf signal. Circuits that perform this function arecalled detectors. Different forms of modulation requiredifferent detector circuits.

Reproduction

Reproduction is the action of converting the elec-trical signals to sound waves that can be interpreted bythe ear.

RECEIVER CHARACTERISTICS

Understanding receiver characteristics is manda-tory in determining operational condition and for com-paring receivers. Important receiver characteristics aresensitivity, noise, selectivity, and fidelity.

Sensitivity

Sensitivity is a measure of receiver’s ability to re-produce very weak signals. The weaker the signal thatcan be applied and still produce a certain signal-to-noise (S/N) ratio, the better that receiver’s sensitivityrating. Usually, sensitivity is specified as the signalstrength in microvolts necessary to cause a S/N ratio of10 decibels, or 3.16:1.

Noise

All receivers generate noise. Noise is the limitingfactor on the minimum usable signal that the receivercan process and still produce a usable output. Ex-pressed in decibels, it is an indication of the degree towhich a circuit deviates from the ideal; a noise figure of0 decibels is ideal.

Selectivity

Selectivity is the ability of a receiver to distinguishbetween a signal at the desired frequency and signals atadjacent frequencies. The better the receiver’s abilityto exclude unwanted signals, the better its selectivity.The degree of selectivity is determined by the sharp-ness of resonance to which the frequency determiningcomponents (bandpass filters) have been engineered

Figure 1-7.—AM superheterodyne receiver and waveforms.

1-8

and tuned. Measurement of selectivity is usually doneby taking a series of sensitivity readings in which theinput signal is stepped along a band of frequenciesabove and below resonance of the receiver’s circuits.As the frequency to which the receiver is tuned is ap-proached, the input level required to maintain a givenoutput will fall. As the tuned frequency is passed, theinput level will rise. Input levels are then plottedagainst frequency. The steepness of the curve at thetuned frequency indicates the selectivity of the re-ceiver.

Fidelity

Fidelity is a receiver’s ability to reproduce the in-put signal accurately. Generally, the broader thebandpass, the greater the fidelity. Measurement istaken by modulating an input frequency with a seriesof audio frequencies and then plotting the outputmeasurements at each step against the audio input.The curve will show the limits of reproduction.

Good selectivity requires a narrow bandpass. Goodfidelity requires a wider bandpass to amplify the outer-most frequencies of the sidebands. Knowing this, youcan see that most receivers are a compromise betweengood selectivity and high fidelity.

AM SUPERHETERODYNERECEIVER

The superheterodyne receiver was developed toovercome the disadvantages of earlier receivers. Ablock diagram of a representative superheterodyne re-ceiver is shown in figure 1-7. Superheterodyne receiv-ers may have more than one frequency-convertingstage and as many amplifiers as needed to attain the de-sired power output.

FM SUPERHETERODYNERECEIVER

Fundamentally, FM and AM receivers functionsimilarly. However, there are important differences incomponent construction and circuit design because ofdifferences in the modulating techniques. Comparisonof block diagrams (figures 1-7 and 1-8) shows thatelectrically there are two sections of the FM receiverthat differ from the AM receiver: the discriminator (de-tector) and the accompanying limiter.

FM receivers have some advantages over AM re-ceivers. During normal reception, FM signals are static-free, while AM is subject to cracking noise and whistles.Also, FM provides a much more realistic reproductionof sound because of the increased number of sidebands.

Figure 1-8.—FM superheterodyne receiver and waveforms.

1-9

SINGLE-SIDEBAND (SSB)

Figure 1-9 is a block diagram of a basic ssb re-ceiver. Though the ssb receiver is not significantly dif-ferent from a conventional AM superheterodynereceiver, it must use a special type of detector and a car-rier reinsertion oscillator. The oscillators in a ssb re-ceiver must be extremely stable. In some cases, afrequency stability of plus or minus 2 hertz is required.You can see that frequency stability is the most impor-tant factor of ssb equipment.

Ssb receivers may use additional circuits that en-hance frequency stability, improve image rejection, orprovide automatic gain control (age). However, thecircuits shown in figure 1-5 will be found in all single-sideband receivers.

AMPLIFICATION

Because the incoming signal may be weak and be-cause a certain minimum voltage level is required forthe auxiliary equipment to operate, considerable am-plification must take place before the receiver output isused to drive speakers, headphones, or terminal equip-ment. This is usually called the gain of the receiver.Gain is a term used to describe an increase in current,voltage, or power. For example, if the detector, whichremoves the desired intelligence, requires 1 volt to op-erate and if the input to the receiver is 1 microvolt, a to-tal amplification of 1 million is required beforedetection. If the loudspeaker requires 10 volts, anothervoltage amplification of 10 is necessary between thedetector and the loudspeaker.

The gain of an amplifier is expressed in decibels(dB). The decibel is a means of measuring relative lev-els of current, voltage, or power. Most often it is used toshow the ratio between input power and output power.This ratio is expressed as gains and losses, where a mi-nus (–) sign placed before dB indicates a loss and a plus

(+)(or no sign at all) indicates a gain. The number ofdecibels change between two power values can be com-puted by the formula:

The comparison of dB’s to power ratio is shown intable 1-3. You can see instantly the reason behind us-ing the decibel system. It is much easier to say the sig-nal level has increased 40 dB than to say it hasincreased 10,000 times.

Examining table 1-3 again, you can see that an in-crease of 3 dB indicates a doubling of power. The re-verse is also true. If a signal decreases by 3 dB, half thepower is lost. For example, a 100-watt signal de-creased by 3 dB will equal 50 watts, while the same100-watt signal increased by 3 dB will equal 200watts. It’s important to understand that no matter howmuch power is involved, a loss or gain of 3 dB alwaysrepresents a halving or doubling of the output power.

Technically, the dB level of a signal is a logarith-mic comparison between the input and output signals.Table 1-4 shows the common logarithms used to calcu-late dB. Normally the input signal is used as a refer-ence. However, sometimes a standard reference signalis used. The most widely used reference level is a 1milliwatt signal. Decibels measured in reference to 1milliwatt are abbreviated dBm. A signal level of 3dBm is 3 dB above 1 milliwatt and a level of-3dBm is3 dB below 1 milliwatt. The formula for dBm is a varia-tion of the dB power formula:

As a Navy technician, you will use the dBm systemof measurement often to perform receiver sensitivity tests. For example, a receiver rated at -110 dBm willdetect a signal 110 dB below 1 milliwatt. Suppose the

Figure 1-9.—Basic ssb receiver.

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Table 1-3.—Decibel to Power Ratio

Table 1-4.—Logarithms

receiver’s sensitivity drops to -107 dBm. Since a loss of3 dB reduces the sensitivity by 1/2, the input signal willhave to be twice as large to be detected.

TRANSCEIVERS

A transceiver is a unit, usually enclosed in a singlecase, that combines a transmitter and receiver using acommon frequency control. Transceivers are used ex-tensively in two-way radio communications at all fre-quencies, and in all modes.

The primary advantage of using a transceiverrather than a separate transmitter and receiver is cost.In a transceiver, many of the components can be sharedduring both transmit and receive operations. Anotheradvantage is that transceivers can be tuned more easilythan separate units.

A disadvantage of using a transceiver is thatwhile duplex operation is not possible with most trans-ceivers, communication must sometimes be carriedout on two different frequencies. Although this is a

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problem with most transceivers, some do have provi-sions for separate transmit and receive operations, al-lowing them to overcome the problem.

ANCILLARY EQUIPMENT

Now that we have looked at the basic componentsof a communications system, let’s identify some of theancillary equipment required to make a transmitter andreceiver useful.

HANDSET

A handset converts acoustical (sound) energy intoelectrical energy, which is used to modulate a transmit-ter. It also converts electrical energy into acoustical en-ergy for the reproduction of the received signal.

To key a transmitter, the push-to-talk button is de-pressed, closing the dc keying circuit, which places thetransmitter on the air. The handset is normally con-nected to a radio set control but can be used locally atthe transmitter. Using the “local” option is a good wayto determine whether a problem exists in the transmit-ter or remote equipment.

RADIO SET CONTROL

The radio set control provides the capability tocontrol certain transmitter functions and the receiveroutput from a remote location. Some control units con-tain circuits for turning the transmitter on and off,voice modulating the transmission, keying when usingCW, controlling receiver output, and muting the re-ceiver when transmitting.

A representative radio set control unit is shown infigure 1-10. As many as four of these units maybe par-alleled to a single transmitter/receiver group to provideadditional operating positions. This setup is oftenfound aboard ship when a transmitter or receiver iscontrolled from various locations like the bridge orcombat information center.

TRANSMITTER TRANSFERSWITCHBOARD

The transmitter transfer switchboard allows the re-mote control station functions and signals to be trans-ferred selectively to the transmitters. Figure 1-11shows a transfer switchboard that allows the functionsand controls of anyone, or all, of 10 remote control sta-tion functions and signals to be transferred selectivelyto any one of six transmitters. Each knob corresponds

Figure 1-10.—Radio set control

Figure 1-11.—Transmitter Transfer Switchboard (SB-988/SRT).

to a remote control station and has 8 operating posi-tions. Positions 1 through 6 correspond to attached

transmitters. The seventh position (X) allows for

switching of the transmitters to another switchboard.The eighth position (OFF) removes the remote from

the system.

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RECEIVER TRANSFER SWITCHBOARD

The receiver switchboard allows the audio outputsfrom the receivers to be transferred to remote controlstation audio circuits. A representative receiver trans-fer switchboard is shown in figure 1-12. This switch-board contains 10 seven-position switches. Eachswitch corresponds to a remote control station andeach switch position (1 through 5) represents a re-ceiver. Position X allows the circuits attached to theswitch to be transferred to another switchboard.

ANTENNAS

An antenna is a conductor or system of conductorsthat radiates or intercepts energy in the form of electro-magnetic waves. An antenna can be simply apiece ofwire; but in practice, other considerations make the de-sign of an antenna system complex. The height aboveground, conductivity of the earth, antenna shape anddimensions, nearby objects, and operating frequencyare just a few of the factors affecting the radiation fieldpattern.

Information on antenna theory, basic antennas,and wave propagation will be available in Antennas &Wave Propagation, volume 7, of this training series.Currently, you can find information in Navy Electric-ity and Electronics Training Series (NEETS), Module10, Introduction to Wave Propagation, TransmissionLines, and Antennas, NAVEDTRA 172-10-00-83.

SYNCHROS AND SERVOS

In many electromechanical systems, the angularposition of a shaft must be transmitted from one loca-tion to another without an actual mechanical linkage.You have seen examples of this in mast-mounted rotat-ing directional antennas and the automatic tuning func-tion of receivers and transmitters from remotelocations. A widely used method employs ac machinesthat operate as single-phase transformers. These ma-chines are called synchros.

Synchro receivers contain sets of gears that do theactual moving of the device to which the synchro is at-tached. These receivers are light-duty devices, de-

Figure 1-12.—Receiver Transfer Switchboard (SB-973/SRT).

signed to move small loads or to produce smallamounts of torque. When the shaft to be driven at theremote location is connected to an indicating device orsome light load, the synchro receiver is capable of de-veloping the necessary torque. But, if the load is aheavy load and more torque is required, torque (power)

amplification is required. A control system capable ofdelivering larger amounts of power or torque is known

as a servo mechanism, or servo.

You will encounter many systems that use sychrosand servos. You can find detailed information aboutthese devices in the Military Standards Handbook,

MIL-HDBK-225 and NEETS, Module 15, Synchros,

Servos, and Gyros, NAVEDTRA 172-15-00-85.

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CHAPTER 2

SYSTEMS EQUIPMENTCONFIGURATIONS

INTRODUCTION

In chapter 1, we discussed basic system requirements. In this chapter, we will look at each equipmentconfiguration. We will then link them together, forming a block diagram of the systems covered. We willdiscuss naval equipment from extremely-low-frequency through super-high-frequency. We also will look atmicrowave communications, the Single Audio System, teletype equipment, portable and pack radioequipment, and the Communications Link Interface Planning System.

At various points in the chapter, we review basic principles associated with the larger topic. The purposeof those reviews is to refresh your memory, in case you have not worked in the area for sometime.

After completing this chapter, you should be able to:

Identify system equipment configurations and how they link together

Recognize various extremely-low-frequency through super-high-frequency naval equipment

Compare a simplex relay system with a duplex relay system in microwave communications

Identify teletype equipment and portable and pack radio equipment

Identify the Communications Link Interface Planning System

SHIPBOARD COMMUNICATIONSOVERVIEW

Shipboard communications are now highlysophisticated. Nearly all the communicationsrequirements for a ship can be met with fewer, moreversatile, pieces of equipment. This versatility cameabout through improved equipment design andinstallation.

As communications equipment became morecapable and complex, the need for an orderly processof identifying equipment by designation becameapparent. The process that was developed identifiedequipment from the system level down to the partlevel. The highest level designator, system, describes

pieces of equipment that work together for a specificfunction. The lowest level designator, part, describesone piece, like a resistor. The following paragraphsdescribe the various levels in greater detail.

SYSTEM

Recall from chapter 1 that a communicationssystem is a collection of equipment used together tosatisfy a specific communications requirement. Further,as the following paragraphs explain, a system is acombination of sets, units, assemblies, subassemblies,and parts. The requirement placed on the system couldbe to send or receive voice, cw, or teletype information.

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Figure 2-1 illustrates the equipment included in atypical system to meet these communicationrequirements.

SET

A SET consists of a unit or units and theassemblies, subassemblies, and parts connected toperform a specific function. Two examples are radioreceiving sets and radio transmitting sets.

GROUP

A GROUP is a collection of units, assemblies,subassemblies, and parts that (1) is a subdivision of aset or system and (2) cannot perform a completeoperational function. A good example is an antennacoupler group.

UNIT

A UNIT is a combination of parts, subassemblies,and assemblies mounted together that can normally

operate independently of other equipment. Anexample of a unit is the power supply.

ASSEMBLY/SUBASSEMBLY

An ASSEMBLY is a combination of two or moresubassemblies joined to perform a specific function. ASUBASSEMBLY consists of two or more parts thatform a portion of an assembly. It can be replaced as awhole, but some of its parts can be replacedindividually.

The distinction between an assembly and asubassembly is not always clear. An assembly maybeconsidered a subassembly when it is part of a larger ormore complex assembly. A computer keyboard is agood example. By itself, it is an assembly. However,it is also a subassembly in a total computer system.Another example you are very familiar with is a circuitcard.

Figure 2-1.—Communications system pictorial view.

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PART size of elf transmitters and antennas makestransmission from submarines impractical.

A PART is one component or a combination of twoor more components. A part cannot normally bedisassembled without being destroyed. Resistors,capacitors, and transistors are examples of parts.

EQUIPMENT CONFIGURATIONS

The wide variety of communications equipmentaboard ship can be overwhelming. This sectionseparates that equipment into types of systems andidentifies typical equipment associated with each typeof system.

EXTREMELY-LOW-FREQUENCY/VERY-LOW-FREQUENCYCOMMUNICATIONS

The extremely-low-frequency (elf) com-munications system is used to send short “phoneticletter spelled out” (PLSO) messages from theContinental United States (CONUS) to submarinesoperating at normal mission speeds and depths. Elf canpenetrate ocean depths to several hundred feet withlittle signal loss. This allows submarines to operatebelow the surface, improving their survivability bymaking detection more difficult.

The elf system is a one-way communicationssystem from CONUS to at-sea submarines. The large

The principal use of the very-low-frequency (vlf)communications system is to provide fleet broadcaststo the submarine fleet and associated ships andactivities thorughout the world. Additional uses are inlong-range navigation and time and frequencybroadcasts.

Vlf Transmit

Vlf transmission is normally considered abroadcast; that is, a one--way transmission, with noreply required. The extent and location of the area to becovered determine the transmitter location and powerout.

For worldwide coverage, the Navy has installedseven transmitters whose power out ranges from 0.25to 2.0 megawatts. These transmitters, such as theAN/FRT-87, can operate in either the interruptedcontinuous wave (icw) or frequency shift keying (fsk)mode. A typical vlf radio transmitting station is shownin figure 2-2.

Vlf Receive

The vlf receive system receives fsk and icw radiotransmissions and then reproduces the intelligence thatwas broadcast. Receivers used for vlf communicationsare the AN/BRR-3, AN/FRR-21, AN/WRR-3, and

Figure 2-2.—Vlf radio transmitting station block diagram.

2-3

URR-R389. Figure 2-3 illustrates a typical vlfreceiving system, using the AN/BRR-3 receiver. Mostsurface ships no longer receive vlf broadcasts.However, you will probably find one of these receiversmounted somewhere in your message center or radioroom.

LOW-FREQUENCY COMMUNICATIONS

The low-frequency (lf) band occupies a very smallportion of the radio frequency spectrum. However, the

Navy’s requirement to provide the best possiblecommunications to the fleet requires operation on allfrequency bands. The low-frequency band is used forlong-range direction finding, encrypted medium- andlong-range communications, and aeronautical radionavigation.

Lf Transmit

The low-frequency transmitter is a part of the FleetMultichannel Broadcast System, operating at high

Figure 2-3.—Typical vlf receiving system.

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power over long distances. It provides eight channelsof frequency-division multiplex rtty traffic on eachtransmission. The AN/FRT-72 transmitter is designedspecifically for this purpose. It produces 50-kW peak-envelope power (25-kW average power) and covers afrequency range of 30 to 150 kHz. Low-frequencytransmitters are normally used only on shore stations.

Lf Receive

The low-frequency receive system receives lfbroadcasts and reproduces the intelligence that wastransmitted. A typical lf receive system is shown infigure 2-4. The antennas receive the lf signal and sendit to the multicoupler and patch panel. Themulticoupler and patch panel (AN/SRA-17 andAN/SRA-49) allow the operator to select differentantennas and connect them to various receivers. In thesystem shown in figure 2-4, the receiver can be eitherthe AN/SRR-19A or the R-2368A/URR. Thesereceivers operate in the frequency ranges of 30 to 300kHz and 14 kHz to 30 MHz, respectively.

The receiver audio is fed to the SB-973/SRRreceiver transfer switchboard. As we explained earlier,this allows the received audio to be connected tonumerous pieces of equipment. In figure 2-4, the audiois connected to either an AN/URA-17 or CV-2460convertor comparator, which converts the receivedsignal to dc for use by the teletype (tty) equipment.From the convertor, the dc signal is fed to a dc patchpanel (SB-1203/UG). The signal can then be sent toany crypto equipment attached to the patch panel. Thecrypto equipment decrypts the signal and routes it tothe red patch panel (SB-1210/UGQ). The signal can

then be patched to a teletype printer for plain textprinting, or to a reperforator, where a paper tape will bepunched and stored for later printing.

HIGH-FREQUENCY COMMUNICATIONS

The high-frequency (hf) band is shared by manydomestic and foreign users. Portions scatteredthroughout the band are assigned to the military. TheNavy’s communications requirements have grownrapidly, severely taxing its portion of the spectrum.Satellite communications has relieved some of thiscongestion and, for some types of service, has replacedhf for long-distance communications, pushing hf into aback-up role. However, even with the use of satellitecommunications, hf will continue to be in high demandfor sometime. We will cover satellite communicationsin chapter 3.

Naval communications within the hf band aregrouped into four general types: point-to-point, ship-to-shore, ground-to-air, and fleet broadcast. All but thefleet broadcast are normally operated two-way.

Point-to-Point

Point-to-point systems provide communicationsover long-distance trunks or via links between fixedterminals. A trunk is normally a message circuitbe tween two po in t s us ing cab le , f ibe r , o rtelephone circuits. A link is a transmitter/receiversystem connecting two locations. The two locationsnormally use directional, high-gain antennas thatincrease the effective radiated power, reduce thechance of interference, and boost the sensitivity of the

Figure 2-4.—Lf receive.

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receiving system. With the path length and directionfixed, propagation factors are simplified. Thisprovides highly reliable hf communications.

powered transmitters, lower noise receivers, and moreefficient antennas.

Fleet BroadcastShip-to-Shore

High-frequency atmospheric communicationsbetween shore stations are relatively easy becauseshore stations have sufficient space for efficientomnidirectional antennas or arrays that provide hfcoverage of large areas. Ship-to-shore hf communica-tions are more difficult because the ship is moving andconstantly changing direction. This change ofdirection and severe space limitations aboard shipsmake the installation of large, efficient hf antennasimpractical.

To overcome these problems, ship-to-shoresystems have two major differences from point-to-point systems. First, shipboard antennas are omni-directional. Second, several frequencies are usuallyassigned for each circuit. If one frequency starts todrop out, another can be selected to match thepropagation path conditions between the ship and theshore terminal.

Ground-to-Air

The use of hf radio for ground-to-air com-munications is similar to its use for ship-to-shorecommunications. An additional problem is that anaircraft moves much more rapidly than a ship. Thisrapid movement (plus additional space limitations)requires that all major circuit im-provements be madeat the ground stations. Examples of improvements thatcan only be made to the ground station are higher

As the name implies, this service involvesbroadcast area coverage from shorebased transmittersto ships at sea. To overcome propagation problems,messages are sent on several frequencies at the sametime (frequency-diversity). Space-diversity withphysically separated receive antennas also helpsovercome propagation problems.

Now let’s look at typical shipboard high-frequencytransmit and receive systems.

Shipboard HF Transmit

The high-frequency transmit signal can containeither voice or teletype information. Figure 2-5 showsa typical shipboard high-frequency transmit system.

The same equipment used to receive teletypemessages on low frequencies (teletype, DC PatchPanel SB-1210/UGQ, crypto equipment, and DCPatch Panel SB-1203/UG) are used to send teletypemessages on the high-frequency system; but of course,in reverse order.

An AN/UCC-1(V) or CV-2460 telegraph terminalconverts a dc signal into a tone signal. This signal is fedto the SB-988/SRT transmitter transfer switchboard. AC1004 transmit keying and control/teletype is used tokey the transmitter during tty operation. Voicecommunications also can be connected to the SB-988/SRT switchboard. The voice communications aredeveloped at a handset connected to the C-1138 radio

Figure 2-5.—Shipboard hf transmit system.

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Figure 2-6.—Shipboard hf receive system.

set control. The output of the radio set control is thenfed to the switchboard.

The transmitter transfer switchboard allowsoperators to select the proper transmitter for theselected frequency. The AN/URT-23 transmitterreceives its input from the switchboard and changesthe signal to a modulated rf signal that is fed to theAN/SRA-34, 56, 57, 58, or AN/URA-38 antennacoupler. The antenna coupler matches the outputimpedance of the transmitter to the input impedance ofthe antenna. Antenna couplers also allow more thanone transmitter to be connected to the same antenna aslong as certain conditions are met. When the signalreaches the antenna, it is radiated into the atmosphere.

Shipboard Hf Receive

A typical shipboard hf receive system is shown infigure 2-6. A transmitted signal similar to the onepreviously discussed is received by the antenna andconverted from electromagnetic energy to electricalenergy. The signal is fed to an antenna patch panelwhere it can be distributed to any number of receivers.

In figure 2-6, a receiver (R-1051/URR, R-2368/URR, or R-1903/URR) converts the rf signal intoeither a teletype signal (fsk) or voice. The receiveroutput is then fed to the SB-973/SRR receiver transferswitchboard. The teletype signal from the switchboardfollows the same path used by the low-frequencysignal we discussed earlier. Identical pieces ofequipment are used. The voice signal from the receiverswitchboard is sent to the C-1138 radio set control and

Figure 2-7.—Vhf transmit and receive system.

fed to a handset. The voice signal also can be sent fromthe switchboard to an AM-3729 remote speakeramplifier and then to a speaker. This allows the user tolisten to the signal without having to hold the handset.

VERY-HIGH-FREQUENCYCOMMUNICATIONS

The Navy uses the very-high-frequency (vhf) bandfor mobile communications such as bridge-to-bridge,among boat crews, and for amphibious operations andlanding parties.

Vhf Transmit

A typical vhf transmit and receive system is shownin figure 2-7. On the transmit side, the operator, at aremote location, talks into the handset. The handset is

2-7

connected to radio set control, C-1138. The radio setcontrol output is fed to transmitter transferswitchboard, SB-988/SRT. The switchboard performsthe same function as it does in the lf and hf systems.The output of the switchboard is connected to thetransmit side of the transmitter/receiver (transceiver),AN/VRC-46 or AN/VRC-80. The transceiver convertsthe input signal to an rf signal for transmission and therf is radiated into the atmosphere by the antenna.

in sight of each other, though the distance traveledby the signal is much greater than for surfacecommunications.

The uhf system uses a transceiver. However, wewill still describe the transmit and receive functionsseparately. Although this description pertains to voicecommunications, uhf equipment can process tty data inthe same way that the hf system does.

Vhf ReceiveUhf Transmit

Again, look at figure 2-7. The incoming signal ispicked up by the antenna. This signal is fed to thereceive side of the transceiver. The transceiver outputis fed to the receiver transfer switchboard. Theswitchboard output is connected to either radio setcontrol or to a speaker amplifier, AM-3729, or both,depending on the user’s preference. The output of theradio set control is fed to the handset and the speakeramplifier output is routed to the speaker.

ULTRAHIGH-FREQUENCYCOMMUNICATIONS

The ultrahigh-frequency (uhf) band is used forline-of-sight (short range) command and controlcommunications. As we stated earlier, line-of-sightmeans that both antennas are aimed at one another,with no obstruction in between.

This band is also used for satellite com-munications. Satellite communications are line-of-sight communications because the antennas remain

A basic block diagram of a uhf transmit systemis shown in figure 2-8. On the transmit side of thenonsecure voice system, the operator at a remotelocation talks into the handset. The handset isconnected to a C-1138 radio set control. The radio setcontrol is connected to an SB-988/SRT transmittertransfer switchboard, which is connected to thetransmitter.

On the transmit side of the secure voice system, theoperator talks into the secure voice remote phone unit(RPU). The RPU is connected to the secure voicematrix, which is the tie point for the connection ofmultiple remote phone units. The matrix output is fedto the secure voice equipment that encrypts theinformation. This encrypted information is then fed toan SB-988/SRT transmitter transfer switchboard.

The transmitter switchboard performs the samefunction we described for previous systems. Theswitchboard output is connected to the transmit side ofthe AN/SRC-20/21 or AN/WSC-3, which is connected

Figure 2-8.—Uhf transmit.

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to an AN/SRA-33 or OA-9123 antenna coupler. Thecoupler output is then fed to an antenna.

Uhf Receive

A basic block diagram of a uhf receive system isshown in figure 2-9. Most of the components are thesame as those used in the transmit function. We will,therefore, identify by specific designator only thecomponents that are unique to the receive function.The receive signal is picked up by the antenna and fedto the receive side of the transceiver through theantenna coupler. The receiver output is connectedto an SB-973/SRR receiver transfer switchboard. It isthen connected to either the nonsecure or secure voicesystem, depending upon the received transmissionmode.

When a nonsecure signal is received, the output ofthe receive transfer switchboard is fed to either theradio set control or to the AM-3729 speaker amplifier,or both, depending on user preference.

If a secure voice transmission is received, theoutput of the switchboard is connected to the secure

voice equipment and decrypted. This output is fed tothe secure voice matrix. The secure voice matrixoutput is fed to the RPU, where the signal is convertedback to its original form.

SUPERHIGH-FREQUENCYCOMMUNICATIONS

As we discussed in the previous chapter, twoprimary uses of the superhigh-frequency (shf) band aremicrowave and satellite communications. TheAN/FSC-79 SHF terminal and satellite com-munications will be covered in the next chapter. In thefollowing paragraphs, we will discuss line-of-sightand tropospheric scatter microwave communications.

MICROWAVE COMMUNICATIONSYSTEMS

Microwave systems, such as the AN/FRC-84 andAN/FRC-170(V), are used to relay multiplex signalsfrom point to point. A simplex relay system pro-vides one-way communications and consists of atransmitting terminal, a certain number of repeaters,

Figure 2-9.—Uhf receive.

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Figure 2-10.—Basic microwave relay system.

and a receiving terminal. Figure 2-10A shows you sucha system. A duplex relay system (figure 2-10B)provides two-way communications by using twosimplex systems, one transmitting in one directionand the other transmitting in the opposite direction.The duplex system is further refined by using asingle antenna for transmitting and receiving. This isdone by using different transmitting and receivingfrequencies and by using a duplexer in thetransmission line.

The rf equipment in terminal and repeater stationsare basically the same. Terminal equipment can beconverted to repeater equipment and vise versa. Let’s

take a look at a typical microwave transmitter andreceiver.

MICROWAVE TRANSMITTER

A typical microwave transmitters shown in figure2-11. In operation, the output of a telephone multiplexterminal, which consists of a frequency multiplexedAM carrier signal, is applied to the terminaltransmitter. This input signal (baseband signal) alsocould be a television signal or any other form of signalto be transmitted. A pre-emphasis network accentuatesthe high frequencies, relative to the low, to improve the

2 -10

Figure 2-11.—Typical microwave transmitter.

signal-to-noise ratio. The insertion amplifier accepts portion of the output power back to the klystron tothe signal, amplifies it, and then applies the signal to the compensate for its nonlinearity. This technique allowsklystron oscillator. With this method, the input signal for optimum performance with modulation densities asdirectly modulates the carrier frequency, resulting in a high as 1200 channels. You should be aware that solid-frequency-modulated wave. The “linearize” couples a state devices are replacing most klystrons.

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MICROWAVE RECEIVER

A typical microwave receiver is shown in figure2-12. Though not shown, sensing and alarm functionsare integral to all microwave communicationsequipment.

During system operation, the signal from the an-tenna passes through a waveguide preselector thateliminates interference from adjacent rf channels. Thesignal then enters a waveguide filter tuned to its fre-quency, which rejects all other unwanted frequencies.Next, the signal passes through an isolator that minim-izes intermodulation noise and holds the VSWR below1.2:1. The signal is then mixed with the local oscillator(LO) output to produce the standard 70-MHz inter-mediate frequency (IF). The IF output is amplitude-limited and applied to an automatic frequency control(afc) discriminator, which controls the frequency ofthe LO. The signal is also applied to an IF discrimina-tor, a de-emphasis circuit, and a squelch circuit thatdisconnects the baseband amplifier and demultiplex-ing equipment if noise increases above a preset level.After the squelch circuit, the signal passes through abaseband amplifier and then to the demultiplexingequipment, where the original intelligence is retrieved.

Microwave communications systems operatingin the shf portion of the frequency spectrum use the

principle that propagation approaches an opticalstraight-line path. Propagation takes place in the loweratmosphere and is affected by meteorological factors.Communications in this medium are usually eitherline-of-sight or tropospheric scatter.

LINE-OF-SIGHT (LOS)

A line-of sight microwave system consists of oneor more point-to-point hops. Each hop is designed to beintegrated into a worldwide communications network.Los system characteristics are as follows:

Propagation—Free space as affected by the tro-posphere.

Communications Capacity/Bandwidth—Up to600-4kHz voice channels; wideband, can accept TV.

Range—Usually 50 to 150 km (31 to 95 statutemiles). This depends upon antenna height, earth curva-ture, and intervening terrain.

RF Power—Usually less than 10 watts.

Antennas—Both transmitting and receivingantennas are horn-driven paraboloids, providing highgain and narrow beam widths. In some applications,plane reflectors are used with the paraboloids.

Figure 2-12.—Typical microwave receiver.

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Reliability—Designed to be operational morethan 99% of the time, including the periods of poorpropagation.

Countermeasures—Because of antenna directiv-ity, the system is difficult to jam. Additionally, the sys-tem should not be susceptible to nuclear disturbances ofthe ionosphere.

Application—Because of the bandwidth capa-bility and minimum site requirements, los is welladapted to moderate distance point-to-point multichan-nel communications (with repeaters), transmission ofclosed circuit TV, transmission of radar informationfrom outlying sites, communications relay betweenlocations in congested areas, and “antenna farms.”

TROPOSPHERIC SCATTER SYSTEM

At microwave frequencies, the atmosphere has ascattering effect on electromagnetic fields that allowsfor over-the-horizon communications. This type ofcommunications is called tropospheric scatter, ortroposcatter for short. Troposcatter takes place mostlyat low altitudes, but some effect takes place at altitudesof up to 10 miles. Under the right conditions,troposcatter can take place over hundreds of miles.

A tropospheric scatter microwave system consistsof one or more point-to-point hops (or sections). Eachhop is designed so it can be integrated into theworldwide communications network of the DefenseCommunications System (DCS). Troposcatter linkshave the following characteristics:

Propagation—Free space as affected by the tro-posphere.

Communications capacity/bandwidth—Up to600 4-kHz voice channels; wideband, can accept TV.

Range—Up to 800 km (500 statute miles).

RF Power—High; up to 75 kilowatts dependingupon bandwidth, quality, and range.

Coverage—Point-to-point only.

Antennas—Both transmitting and receivingantennas are horn-driven paraboloids providing highgain and narrow beam widths.

Reliability—Designed to be operational morethan 99% of the time, including periods of poor propa-gation.

Countermeasures—Extremely difficult to jam.Should not be susceptible to nuclear disturbances of theionosphere.

Application—Meets the communications re-quirements between HF sites within its minimumskywave one-hop distance of about 400 miles and line-of-site of about 30 miles. It is especially useful whereconditions prevent the use of line-of-sight communica-tions or if adverse propagation conditions interfere withother transmission methods.

MULTIPLEXINGAs we mentioned earlier, the rf spectrum has

become very congested. The maximum number oftransmissions taking place in the rf spectrum is beingincreased through the use of m u l t i p l e x i n g .Multiplexing refers to the simultaneous transmissionof two or more messages over the same medium orchannel at the same time. Multiplexing may beachieved in various ways, but the most common meth-ods are time-division multiplexing (tdm) and fre-quency-division multiplexing (fdm). Although severaltypes of multiplexing equipment are available in thefleet today, the AN/UCC-1D is the most common.

TIME-DIVISION MULTIPLEXING

Time-Division Multiplexing (Tdm) is a method ofcombining analog signals for serial transfer. The signalsare sampled at intervals and interwoven for transmis-sion. The speed of this multiplexed signal is faster thanthe original individual channel speed by a multipleequal to the number of combined signals. For example,if 5 signals are multiplexed, the data speed of each sig-nal must be multiplied by 5 to keep the signals in syn-chronization. Tdm also results in an increase in thesignal bandwidth because of the increased data speed.

Time-division multiplexing also can be used withdigital signals, but this method is usually calledsynchronous multiplexing.

FREQUENCY-DIVISION MULTIPLEXING

Unlike tdm, which samples a portion of the sinewave, frequency-division multiplexing (fdm)transmits and receives for the full 360 degrees of thesine wave. A channel is subdivided into smallersegments of equal size, called subchannels. Eachsubchannel carries a separate signal. Fdm used by theNavy can generally be divided into two categories,voice and tty communications. You can find moreinformation on multiplexing in NEETS, volume 17.

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SINGLE AUDIO SYSTEM (SAS)

The Single Audio System (SAS) was developed tofulfill the requirement for an integrated secure/non-secure shipboard voice communications system. Itconsists of telephone sets, voice-signal switching de-vices, various control devices, and field changes toexisting equipment, in conjunction with other ele-ments of the overall shipboard radio communicationssystem. The SAS is essentially the baseband (AMand/or FM ) hf, vhf, or uhf audio subset of the ship-board exterior communications system. It incorporatesvoice communications circuits, user control over theoperating mode (both secure and nonsecure), andvarious degrees of operator control over voice circuitselection. Figure 2-13 shows the major equipmentgroups, subsystems, and their interrelationship.

There are two versions of SAS: an automatedsystem (ASAS) and a manual system (MSAS). Thevoice switching equipment and means provided foruser control over circuit selection are the two primarydifferences. Information in this section applies to bothASAS and MSAS, unless otherwise specified.

There is no specific list of equipment that makeupevery SAS installation. There can be different typesand quantities of equipment in each of the groupsidentified in figure 2-13. Equipment types andquantities are dictated by the communicationsrequirements of individual ships and ship classes. Thepublication, Operation and Maintenance Instructions,Single Audio System, NAVELEX EE109-CA-OMI-010/El10 SAS, identifies, in tables 1-1 and 1-2, theSAS equipment commonly used in the fleet.

SYSTEM CAPABILITIES

The SAS incorporates basic capabilities for settingup and operating voice communications circuits. AnSAS installation provides the unique capability tocommunicate in a secure or nonsecure mode, at thediscretion of the operator, from a single telephone orNTDS device. This single audio interface with variouscrypto or plain subsystems is the essence of the SAS.The SAS provides the following options:

The user can select the transmit operating modeexcept for FLTSATCOM secure voice andPLAIN configurations.

The system can notify the user of the transmitoperating mode selected, both visually and withaudio indications.

The system can notify the user by visual indica-tion if the voice station equipment is not con-nected to a crypto or plain subsystem.

The system can notify the user of any incomingsecure (CIPHER) signals by both visual andaudio indications except for the FLTSATCOMsecure voice configuration.

The user can select a voice channel and have itindicated visually.

In addition to these capabilities, the ASAS versionhas the following features:

A processor controlled, programmable voice

Figure 2-13.—Single Audio System (SAS).

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A voice switch self-test and fault location read-out (built-in test).

An audio indication to the user when the voiceswitch built-in-test (BIT) detects a trunk lineshort.

A technical control monitor phone, incorpo-rated into the voice switch, which can access allvoice channels.

SYSTEMS EQUIPMENT AND LOCATION

The following paragraphs provide a briefdescription of the major equipment included in atypical SAS installation. Figure 2-13 illustrates theaudio path of the system and the order in which we willdiscuss the equipment.

User Station Equipment

User station equipment is located in operationscenters throughout the ship, like the bridge, combatinformation center (CIC), flag plot, secondary corm,and other stations where exterior voice com-munications are required by the ship’s mission. Thisequipment consists of telephone sets, audio amplifiers,loudspeakers, headsets, recorders, audio jackboxes,Naval Tactical Data System (NTDS) consoles andintercom units, and local switching devices for addedsystem flexibility.

Voice Switching Equipment

The voice switching equipment is a majorcomponent of the SAS. It is the interface and primaryswitch between the user’s equipment and all crypto andplain subsystems. It is designed for very highinterchannel isolation, which is a TEMPESTrequirement for all equipment that handle both secureand nonsecure signals at the same time. (The ASASand MSAS use different switches for this purpose.)

Crypto and Plain Subsystems

The various crypto and plain subsystems arelocated in the main communications spaces.Cryptographic devices and other “red” equipment arelocated in a secure area within these spaces. There arefive crypto and plain subsystems used within the SAS:NESTOR, VINSON, PARKHILL, FLTSATCOMsecure voice, and PLAIN ONLY. Additional classifiedinformation on these subsystems is available on aneed-to-know basis.

Transmitter and Receiver Transfer Switchboards

These equipment are part of the overall exteriorcommunications switching system and are located inthe main communications spaces, generally in thevicinity of the technical control working area. Theswitchboard equipment group interconnects cryptoand plain subsystem equipment with the appropriateradio equipment. You should recall from chapter 1 thatthese switchboards are also the interconnecting pointsfor other subsystems within the overall exteriorcommunications system. Therefore, they are notunique to the SAS.

Transmit and Receive Radio Equipment

These equipment may be located in both the maincommunications spaces and in separate rooms locatedin various parts of the ship. This equipment groupconsists of the various transceivers, transmitters, andreceivers used for voice nets. The more commontransceivers you will encounter are the AN/SRC-20series, AN/VRC-46, AN/WSC-3(V)3 and (V)7,AN/URC-93, and AN/WSC-6. Common transmittersinclude the AN/URT-23, AN/URT-24, T-1322/SRC,and AN/GRT-21. Common receivers are the R-1051series, R-1903, and AN/GRR-23. For additionalinformation on individual equipment, refer to thatequipment’s technical manual.

TELETYPEWRITER/FACSIMILE EQUIPMENTIn chapter 1, we discussed different methods of

voice communications. Sometimes, the message is toolong for practical transmission by voice, so to get yourmessage or idea across, you may need to use a chart,map, or photograph. Teletype (tty) and facsimile(FAX) equipment allow us to do this.

In the following paragraphs, we will discuss somecommon terms associated with tty and FAXequipment. We will then look at some basic systems.

MODES OF OPERATION

There are two basic modes of teletypewriteroperation: asynchronous (start-stop) and synchronous.The asynchronous mode is the most common. Thesynchronous mode is used primarily in high-speed datasystems.

Asynchronous Mode

In this mode, the receiving device is only allowedto run for one character and is then stopped to await thestart signal for the next character. Any differences inspeed between the transmitting and receiving devicescan only accumulate during the time assigned to one

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character. There is a penalty for this advantage.Character length is increased to include the start(space) and stop (mark) signals. These start and stopsignals are part of the five unit code (BAUDOTCODE) shown in figure 2-14.

Synchronous Mode

Synchronous systems have an advantage overasynchronous systems. The start and stop elements arenot used. This allows more room for informationtransmission. Time is not wasted on start and stopunits. Additionally, this mode has a higher capacity toaccept distorted signals because it does not depend onthe start and stop signals for timing.

MODULATION RATE

The terms used in referring to tty modulation ratesor signaling speeds are baud, words per minute (wpm),and bits per second (bps). Baud is the only term that istechnically accurate. The others are either ap-proximations or require explanation.

Baud

By definition, the word baud is a unit ofmodulation rate. To find the modulation rate of a signalin bauds, divide 1 by the time interval of the shortestunit in the signal. For example, 22 milliseconds (.022see) is the time interval of the shortest unit in the five-unit code at 60 wpm. To find the number of bauds equalto 60 wpm, divide 1 by .022. Rounding off the resultsprovides the figure 45.5, which is the baud equivalentof 60 wpm. You can see that increasing the wpm meansthe unit time interval has decreased.

The most common baudot data speeds range from45.45 to 100 bauds, or about 60 to 133 wpm. Higherspeeds are obtained using the American NationalStandard Code for Information Exchange (ASCII).This is a seven-unit digital code used for thetransmission of teleprinter information. ASCII is usedprimarily with computer systems, but it is also used insome teletypewriter applications. The DefenseCommunications System standard speed for teletypeoperation is 100 wpm or 75 baud.

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Words per minute is used only when speaking ingeneral terms about an approximation of speed. At aspeed of 100 wpm, 100 five-letter words with a spacebetween them can be transmitted in a 60-secondperiod. But, you can also get this wpm rate by varyingthe modulation rate or the length of individualcharacters. Because of this, the baud method ofreference rather than wpm is used.

Bit

In binary signals, the term bit is equivalent to oneplace in a binary number. Because of the influence ofcomputer language, modulation rate is sometimesexpressed as bits per second (bps). When it is expresslyunderstood that each unit in the baudot character is thesame length, the modulation rate expressed in bps isthe same as the modulation rate expressed in baud.

DC CIRCUITS

The two most common methods of creating themark and space conditions are neutral and polaroperation. In neutral operation, current flow representsthe mark and no current flow represents the space. Inpolar operation, current impulses of one polarityrepresent the mark and impulses of the opposite polarityrepresent the space.

Neutral circuits use the presence or absence ofcurrent flow to convey information. These circuits usehigh level (60/20 milliamperes) as the line currentvalue. (Low level operation uses (±6 vdc at 20 micro-amps and can be balanced or unbalanced). A neutralteletypewriter circuit consists of a transmitting device,a current source, a variable resistor to control current, areceiving device, and a transmission line.

Polar operation differs from neutral operation. In apolar system information is always present in either apositive or negative condition. The circuit compositionis the same, but polar operation requires an additionalcurrent source. This current source is usually a solid-state dc power supply that provides variable current tothe teletypewriters. The extra current source normallyprovides current from the positive side for marks andcurrent from the negative side for spaces.

There are some advantages to using polar circuitsrather than neutral circuits. In a polar circuit, it isalmost impossible to distort a signal by high reactance,low-line currents, or random patching of circuits orequipment. A big advantage for the ET is that a com-plete loss of current (a zero reading on the milliamme-Figure 2-14.—Mark and space signals in the teletypewriter-

character R.

ter) quickly indicates line or equipment trouble. Usingneutral signaling, this may only indicate that a steadyspace is being transmitted. This condition is known asrunning open. The teletype appears to be runningbecause it is decoding the constant spaces that causethe type hammer to continually strike the type box, butthere is no printing or movement across the page.

BASIC SYSTEMSWhen teletypewriters are wire-connected

(looped), the exchange of information between them isdirect. When they are not physically joined, exchangeof information is more complex. Dc mark and spaceintervals cannot be sent through the air. The gapbetween the machines must be bridged usingtransmitters and receivers. The transmitter carrier

wave is used to carry the mark and space information.A keyer is used to change the dc pulses from the tty intomark and space modulation for the transmitter carrierwave. The receiver and a convertor are needed tochange the rf signal back to dc pulses.

RADIO ACTUATED TELETYPE(RATT) SYSTEMS

The Navy’s two basic RATT systems are the tonemodulated system known as audio frequency tone shift(AFTS), and the carrier frequency shift system knownas radio frequency carrier shift (RFCS). The RFCS sys-tem is commonly called frequency shift keying (fsk).

For fsk systems, the transmitter provides a sourceof rf excitation. Figure 2-15 illustrates a basic fsk

Figure 2-15.—Basic carrier frequency shift (RFCS) system.

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system. You will find that the keyer is part of thetransmitter in modern systems. The keyer shifts thesignal below or above the assigned frequency,corresponding to the mark or space required for ttytransmission. Usually, the keyer is adjusted for 850 Hz(425 Hz above and 425 Hz below the assignedfrequency). A space will be 425 Hz above and a markwill be 425 Hz below the operating frequency.

AFTS systems use amplitude modulation tochange dc mark and space pulses into audio. A basictone-modulated system is shown in figure 2-16. Theaudio conversion is done by an audio oscillator in thetone convertor. Varying the tone according to thecharacters transmitted from the tty equipment

amplitude-modulates the transmitter carrier wave. The

receiver demodulates this signal, separating the audio

signal from the carrier.

In both the RFCS and AFTS systems, the tty

signals pass through the panel that controls looping

current. Looping current is the current supplied by the

tty solid-state power supply. The tty panel integrates

the tone-modulated and carrier-frequency shift

systems. By allowing the tty equipment to be set up in

any configuration desired, this panel gives the

operators maximum operational flexibility with the

least amount of circuitry and equipment.

Figure 2-16.—Basic tone-modulated (AFTS) system.

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SIMPLEX RFCS TELETYPE SYSTEM

A simplex communications circuit consists of asingle channel, which may have two or more stationscommunicating over it. However, they cannotcommunicate at the same time. The stations have toalternate using the channel.

RFCS teletype systems are used in the lf to hf bandfor long-range communications. To reduce fadingand interference, the Navy uses two methods ofdiversity reception called space diversity a n dfrequency diversity. In space diversity reception, the

transmitted signal is received by two or more antennasspaced at distances greater than one wavelength.Because of the spacing requirements, space diversity isnormally limited to shore stations. In frequencydiversity, two or more signals are transmitted ondiffering frequencies, but carry the same intelligence.Another type of frequency diversity is called a fdiversi ty or tone diversi ty and is used withmultichannel broadcasts.

A simplified block of a simplex RFCS system isshown in figure 2-17.

Figure 2-17.—Simplex RFCS system.

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RFSC SEND Patch Panels

In the following paragraphs, we will discuss theequipment shown in the RFCS transmit (send) systemin figure 2-18.

Teletypewriter Sets

The Model 28 family and the AN/UGC-143 seriesare the two tty sets currently used by the Navy.Although the AN/UGC-143 is not shown in figure2-17, we will discuss its characteristics later. There areseveral tty sets included in the Model 28 family withvarying weights and sizes. They feature high operatingspeeds, quiet operation, and are particularly suited forshipboard use under the severe conditions of roll,vibration, and shock.

Model 28 tty’s may be composed of the followingcomponents, depending upon their specific function: acabinet, keyboard, page printer, typing perforator,transmitter distributor, typing reperforator, powerdistribution panels, and power supply.

All equipment components are housed in thecabinet. Transmissions are initiated through thekeyboard or transmitter distributor. Received signalsare printed on the page printer . Monitoredtransmissions can also be printed on the page printer.The typing perforator and reperforator are used forpreparing tapes that can be stored for futuretransmission through the transmitter distributor.

The AN/UGC-143A(V) is also known as the NavyStandard Teleprinter (NST) and has the followingcharacteristics:

Fully automated

Accepts Baudot code or ASCII

Bulk storage unit contains tape drives similar tothose found in the AN/USH-26

Can be configured to interface with Navystandard personal computers

Fully compatible with current crypto devices

Capable of supporting paper tape operations

Tty panels SB-1203/UG and SB-1210/UGQare used for interconnection and transfer ofshipboard tty equipment. The SB-1203/UG is ageneral-use panel and the SB-1210/UGQ is intendedfor use with crypto. In addition, tty panels furnish acentral point for connecting the dc supply into theteletypewriter circuits. So, one source of supply canbe used for all the circuits passing through aparticular panel.

One procedural note: Anyone patching orunpatching circuits from a tty panel must be sure topull the plug from the looping jack beforeremoving the other plug from the set (machine)jack. Pulling the set jack first interrupts all ttymessage traffic on that channel. I T A L S OPRODUCES A DANGEROUS DC VOLTAGEON THE EXPOSED PLUG!

Cryptographic Equipment

Cryptographic equipment is used to encode anddecode messages that require security handling. To dothis, the crypto equipment must be compatible on boththe transmit and receive ends.

Remote Transmitter Control

The remote transmitter control unit is mountedclose to the tty keyboard, and permits remotecontrol of the transmitter. For RFCS operation, theoperator sets the three-position rotary switch toCFS SEND to transmit and CFS REC for receiv-ing. The TONE S/R position is used for AFTStransmit and receive.

Transmitter Switchboard

The SB-863/SRT switchboard is used in thissystem to connect the remote transmitter control to thetransmitter to be used.

Transmitter

The transmitter is used to transmit the RFCSsignal. It is important that the operator tune thetransmitter to the proper frequency.

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Figure 2-18.

2-21

RFCS RECEIVE SYSTEM

The RFCS receive system shown in figure 2-19 isused to receive the transmitted signal and convert itback to a usable tty output.

Antenna Filter

The antenna filter receives the rf signal from theantenna and filters out any unwanted signals so onlythe proper band of frequencies are passed on to thereceiver.

Radio Receiver

The receiver translates the rf signal to an audiosignal.

Receiver Transfer Switchboard

The switchboard is used to connect the receiver toany one of the convertors in the convertor group.

Convertor/Comparator Group

The convertor/comparator group is used withreceivers in either space diversity or frequencydiversity operation to convert the frequency shift afsignal from the receiver into dc pulses that open andclose the dc loop according to the mark and spacecharacters received. When the system is not usingdiversity operation, each convertor can be used with aseparate receiver.

Figure 2-19.—RFCS receive system.

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The comparator section of the convertor comparesthe signals received in the diversity mode and allowsonly the stronger signal to be passed on to thecommunication patch panel.

Communication Patch Panel

The communication patch panel performs thesame function on the receive side as it does on thetransmit side.

Crypto Equipment

The crypto equipment decodes the received signalso it can be printed out in its original form.

Teletype

The tty equipment converts the dc pulses from thepatch panel to a printed copy of the original message.The tty shown is a page printer only and does not havetransmit capability.

AFTS SYSTEM

Figure 2-20 is a block diagram of a half-duplex uhfsystem. Half-duplex communication can be ineither direction, but cannot happen at the same time.The term half-duplex is qualified by adding send only,receive only, or send or receive.

AFTS Transmit

Dc signals from the tty are sent to the com-munications patch panel where they are fed to the toneterminal set. The tone terminal set converts the dcsignals into audio tone-shift signals. The audio tone-shift signals are patched to the transmit side of thetransceiver through the transmitter t ransferswitchboard. The audio tone-shift signals are then usedto modulate the rf carrier for transmission.

AFTS Receive

The rf tone-modulated signals are received at theantenna and then patched, via the multicoupler, to thereceive side of the transceiver, where demodulation toaudio tone-shift signals takes place. The signals arethen patched to the tone terminal set through the re-ceiver transfer switchboard, where they are convertedback to dc signals. The dc signals are then patchedthrough the communication patch panel to the tty.

FACSIMILE

Facsimile (FAX) is a method of transmitting stillimages over a communications system. The imagesmay be weather maps, photographs, sketches,typewritten or printed text, or handwriting. Military

use of FAS is primarily limited to transmission andreception of weather maps. Because of longtransmission times, its tactical uses are limited.

TEMPEST

Compromising emanations, generally calledTEMPEST, are unintentional data-related orintelligence-bearing signals which, if intercepted oranalyzed, can disclose the classified informationtransmitted, received, handled, or otherwiseprocessed by electrical information processingequipment or systems.

The Navy uses MIL-STD-1680 (SHIPS),Installation Criteria for Shipboard Secure ElectricalProcessing Systems, as the guide for TEMPEST.Within communications centers, ETs must understandand be familiar with both RED and B L A C Kdesignated systems and equipment. The RED andBLACK designations are explained in the followingparagraphs.

RED CRITERIA

The RED designation applies to all crypto

equipment, subscriber terminal equipment, and

interconnecting conductors involved in processing

classified plain language information. It also applies

Figure 2-20.—Half-dup1ex AFTS teletype system.

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to primary power circuits, dc circuits, control wiring,and ground conductors serving cryptographicequipment and subscriber terminal equipment that aredesignated RED.

The RED designation also applies to junctionboxes, distribution frames, terminal boxes, conduit,ducts, cable racks and hangers, patching and switchingpanels, cabinets, power distribution panels (both acand dc), and other ancillary equipment serving theconductors and equipment mentioned above.

Primary Red

Any conductor intended to carry classified plainlanguage terminating in RED equipment or the REDside of crypto equipment is designated PRIMARYRED.

Secondary Red

Any conductor, other than PRIMARY RED, thatconnects to RED equipment, the RED side of cryptoequipment, or the RED side of isolation devices, anddoes not intentionally carry classified information, butbecause of the coupling mechanism with the REDequipment might carry compromising information, isdesignated SECONDARY RED. Some examples youare probably familiar with are indicator lines, andcontrol and timing lines. Power distribution panels and

grounding systems serving RED conductors are alsodesignated SECONDARY RED.

BLACK CRITERIA

The BLACK designation applies to all conductorsand equipment involved in handling or processingunclassified plain language and encrypted informationin electrical form. It also applies to all facilities andcircuits that are not designated RED.

PORTABLE AND PACK RADIOEQUIPMENT

Because portable and pack radio sets mustbe lightweight, compact, and self-contained, theyare usually battery- or generator-powered, have lowoutput power, and are either transceivers ortransmitter-receivers. Navy ships and Special Forcescarry a variety of these radio sets for amphibious andemergency communications, with the equipment typevarying according to the needs of the ship or command.The following paragraphs introduce some of theseequipment.

AN/CRT-3A

Radio transmitter AN/CRT-3A, popularly knownas the “Gibson girl,” is a rugged emergency transmittercarried aboard ships and aircraft for use in lifeboatsand liferafts. Shown in figure 2-21, it operates on the

Figure 2-21.—Emergency Transmitter AN/CRT-3A.

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international distress frequency (500 kHz) and thesurvival craft communication frequency (8363 kHz).No receiving equipment is included.

AN/PRC-70

The AN/PRC-70 is a multimode (FM, CW, FSK,SSB, AM) manpack radio set operating in the 2.0-to75.9999-MHz frequency range.

AN/PRC-77

The AN/PRC-77, shown in figure 2-22, is an FM,short-range, 920 channel vhf radio operating in the 30-to 75.95-MHz frequency range. Figure 2-22 (view A)shows the pack frame, the handset, and accessorypouch. View B shows the transmitter-receiver. Whennot in use, the equipment is stored in a specialaluminum case.

AN/PRC-96

The AN/PRC-96 portable transceiver, shown infigure 2-23, is dual-channeled, battery-powered, andprovides homing and two-way voice communicationsbetween liferafts and searching ships and aircraft, onthe 121.5 and 243 MHz “guard” channels.

AN/PRC-104

The AN/PRC-104, shown in figure 2-24, is a

lightweight radio transceiver that operates in the hf

band and can be tuned from 2.0 to 29.9999 MHz. It

operates in the ssb (usb or lsb) modes for voice

communications, CW for Morse code, and FSK for

Figure 2-22.—Radio Set AN/PRC-77. Figure 2-23.—Transceiver AN/PRC-96.

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Figure 2-24.—Transceiver AN/PRC-104.

transmission of tty or other data. It can be used in theman-pack configuration or can be configured forvehicular or fixed station operation.

Unlike older radio sets, there are no front panelmeters or indicator lights on the AN/PRC-104. Allfunctions are monitored by the radio itself andcommunicated through the handset in the form ofaudio tones. This is extremely useful during tac-tical black-out operations. Newer versions of the

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AN/PRC-104 have modified the R/T section of theradio, but the above information still applies.

AN/PRC-113

The AN/PRC-l13 is a two-band (vhf and uhf)amplitude modulated transmitter-receiver, whichoperates at 116.0 through 149.975 MHz in the vhf bandand 225.0 through 399.975 Mhz in the uhf band.When interfaced with TSEC/KY-57 crypto

equipment, this radio can operate in AM voice, or AMsecure voice.

AN/PRC-117

The AN/PRC-117 Full-Band Frequency-HoppingVHF-FM Manpack Transceiver with integratedCOMSEC, shown in figure 2-25, operates in the 30-to

89.975-MHz frequency range and contains a built-inCOMSEC capability that is compatible with VINSONKY-57/58 equipment.

Frequency-hopping is an advanced method ofECCM (Electronic Counter-Counter-Measure). Youshould remember that a standard FM transmission iscentered on a specific carrier frequency, which meansit can be easily detected, monitored, or jammed. In

Figure 2-25—Transceiver AN/PRC-117.

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frequency hopping, no single carrier is used. Instead,the transmitter hops around the band in a randompattern, spending only a few milliseconds on any onefrequency. This makes the signal difficult to detect andextremely difficult to monitor or jam.

AN/PSC-3

Backpack radio set AN/PSC-3 is a portable,battery-powered, half-duplex uhf transceiver operat-ing in the 225.0- to 399.995-MHz range. It providestwo-way voice (secure and plain) and data com-munications via satellite relay (SAT) or line-of-sight(los) modes. Radio set AN/PSC-3 components areshown in figure 2-26.

One important feature of the AN/PSC-3 is itsability to interface directly with the AN/PRC-70,AN/PRC-77, and other vhf-capable radios, whichprovides a satellite link for vhf tactical equipment.This provides away to retransmit vhf information fromone of these radios by (1) converting vhf to uhf, (2)transmitting through a satellite to another AN/PRC-3,(3) demodulating it and passing it directly to another

Figure 2-26.—Radio Set AN/PSC-3.

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AN/PRC-70/77, which could then (4) retransmit theinformation as vhf. This greatly enhances com-munications capability and extends the com-munications range. A basic retransmission setup isshown in figure 2-27.

DIGITAL MESSAGE DEVICE GROUP(DMDG)

The DMDG is part of the Special Forces BurstCommunications System. It is used with radio setsAN/PRC-70/74 and AN/PSC-3 to send and receivemessages. Messages are typed on the KY-879/Pkeyboard (shown in figure 2-28), which displays themessage as it is being typed and stored in memory.When the message is ready to be sent, the operatorselects the proper mode and the device converts themessage to digital information. The digital in-formation is sent to one of the above radios fortransmission. After the information is received at theother end, it is sent to another KY-879/P, where themessage can be read on the device’s display screen.

The device can send messages at 300 or 1200 baudin the satellite mode and 266.6 baud when connected tothe AN/PRC-70/74.

INTRODUCTION TOCOMMUNICATIONS LINK

INTERFACE PLANNING SYSTEM(CLIPS)

The Communications Link Interface PlanningSystem (CLIPS) was introduced to the Joint SpecialOperations Community in 1986. CLIPS is a systemdesigned to help the communications planner

Figure 2-27.—Basic retransmission scheme.

Figure 2-28.—KY-879/P keyboard.

determine interoperability in joint operationsinvolving single-channel tactical radio equipment.

Equipment planning in the Special OperationsCommunity is complicated by the wide variety ofequipment used and the highly variable and rapidlychanging nature of the operational settings. Becausemost communications requirements for thiscommunity are satisfied by single-channel, full-duplex radio links, CLIPS was designed primarily tohelp plan this type of communications link. Equipmentcovered under CLIPS is specifically limited to radios,modems, crypto devices, input/output data terminals,and packet controllers normally used to establish theseradio links.

The CLIPS program is designed for use with IBM

PC or compatible computers using MS-DOS. It is

designed to provide solutions to equipment planning

and link configuration problems by considering all the

factors involved and automatically determining the

“best” system to be used by each participant in the

communications link. The CLIPS program in-

corporates the knowledge of experienced com-

munications personnel, equipment specifications,

circuit planning rules, and equipment inventories in a

way that makes communications planning straight-

forward, easy, and objective.

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CHAPTER 3

SATELLITE COMMUNICATIONS

INTRODUCTION

In the past, the Navy relied upon hf communications as its primacy method of sending messages. With theovercrowding of the hf spectrum, the need for new and advanced long-range communications becameapparent. Satellite communications (SATCOM) systems have shown they can provide survivable, reliable,high-capacity, secure, and cost-effective telecommunications for the military.

In this chapter, you will be introduced to satellite communications fundamentals, fleet SATCOM sub-systems, shore terminals, current and future satellites, and some specific SATCOM equipment and racks.SATCOM is a natural outgrowth of modern technology and the continuing demand for greater capacity andhigh-quality communications. This information will be crucial to you in understanding the communicationstechnology of both today and the future.

After completing this chapter, you should be able to:

Recognize satellite communications fundamentals

Identify fleet SATCOM subsystems and shore terminals

Evaluate specific SATCOM equipment and racks

SATELLITE COMMUNICATIONSFUNDAMENTALS

(A passive satellite simply reflects radio signals backto earth.) One station transmits to the satellite on theuplink frequency. The satellite translates the signal tothe downlink frequency, amplifies the signal, thentransmits it to the receiving terminal. Figure 3-1 shows

A typical SATCOM link uses an active satellitethat receives and retransmits, and two earth terminals.

Figure 3-1.—Satellite communications system.

3-1

some of the various earth terminals and how theyinterface. The end use or purpose determines thesystem’s complexity and how the system is used.

ROLE OF SATELLITECOMMUNICATIONS

SATCOM links, one of several kinds of long-distance communications links, interconnect com-munications centers located strategically throughoutthe world. These SATCOM links are part of theDefense Satellite Communications System (DSCS)and Fleet Satellite Communications.

Satellite communications systems are veryimpor tan t to the wor ldwide mi l i t a ry com-munications network for two primary reasons. First,they continue to operate under conditions that causeproblems for other methods of communication.Second, they provide reliable and secure com-munications to previously inaccessible areas. Inmany cases, these communications requirementscan on ly be satisfied by sophisticated satellitecommunications systems. By satisfying such needs,SATCOM makes a significant contribution to theimproved reliability of naval communications.

ADVANTAGES OF SATELLITECOMMUNICATIONS

Some of the unique advantages SATCOM has overconventional long-distance communications are asfollows:

SATCOM links are unaffected by thepropagation problems associated with hf radiocommunications.

SATCOM links are free from the high-attenuation problems of facilities that use wireor cable for routing communications.

SATCOM links span long distances.

The numerous repeater stations required forline-of-sight and troposcatter systems are notneeded.

As you can see, satellite links provide the requiredflexibility and reliability needed to support militaryoperations. In the following paragraphs, we will lookat SATCOM capacity, reliability, vulnerability,flexibility, and limitations.

Capacity

Currently, military SATCOM systems can providecommunications between backpack, shore, airborne,and shipboard terminals. These SATCOM systems canhandle thousands of communications channels at thesame time.

Reliability

SATCOM frequencies are only slightly affectedby atmospheric phenomena and do not depend onreflection or refraction. Reliability is based on the skillof operators and maintenance personnel and thecondition of the satellite communications equipment.

Vulnerability

Communications satellites are relatively safe fromthreats of harm. Because these satellites are in suchhigh orbits, any attempt to disable or destroy themfrom the Earth would be difficult and expensive.However, Earth terminals are a different story. Theyoffer a more attractive target for destruction byconventional methods. But these terminals can beprotected by the same methods taken to protect othervital installations. So overall, the satellite system isnearly free from harm by an enemy.

Operationally, highly directional earth terminalantennas provide a high degree of freedom fromjamming. The wideband system can use antijammingtechniques, which also reduces vulnerability.

Flexibility

Mobile military satellite earth terminals withtrained crews can be deployed and put into operationanywhere in the world within hours.

Limitations

The technical characteristics of the satellite and itsorbital parameters are the main limitations to a satellitecommunications system. Two additional limitingfactors for active satellites are transmitter power andreceiver sensitivity. Energy for electricity is limited towhatever can be produced by the solar cells, whichlimits the satellite’s output power. This problem ismade worse by users who increase their output powerto the satellite, causing the satellite to try to retransmitat the new power level, at the expense of reducingsignals to other users.

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FLEET SATELLITECOMMUNICATIONS

T h e F l e e t S a t e l l i t e C o m m u n i c a t i o n s(FLTSATCOM) System provides communications,via satellites, between designated mobile units andshore sites. These links provide worldwide coveragebetween the latitudes of 70 degrees north and 70degrees south. Three satellites are currently in use witha fourth to come online soon: GAPFILLER, LEASAT,FLTSATCOM, and UHF Follow-on (UFO).

System installations are located on ships,submarines, mobile vans, aircraft, and shore stations.Though these installations could operate separately,integrating the system provides message traffic andvoice communications to all DOD long-rangecommunications networks. In addition, certain shorestations provide a back-up capability to other users incase of an outage of any kind, which maintains netconnectivity.

The Navy SATCOM system consists ofinformation exchange subsystems that use thesatellites as (1) relays for communications and control,and (2) quality monitoring subsystems that providedata required to manage satellite resources. Eachsubsystem is structured for specific navalcommunications requirements. The followingsubsystems make up most of the Navy’s FLTSATCOMsystem.

Fleet Satellite Broadcast Subsystem. This is anexpansion of the “Fleet Broadcast,” which hasbeen the central communications medium foroperating naval units.

Common User Digital Information ExchangeSubsystem (CUDIXS) and Navy ModularAutomated Communications Subsystem(NAVMACS). These two installations form acommunications network for transmittinggeneral-service message traffic between shipsand shore installations.

Submarine Satellite Information ExchangeS u b s y s t e m (SSIXS) . T h i s s u b s y s t e mcompliments other communications linksbetween SSBN and SSN submarines and shoreterminals.

Secure Voice Subsystem. This is a narrowbanduhf subsystem that links voice communicationsbetween ships and connects with wide-areashore voice networks.

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Tactical Intelligence Subsystem (TACINTEL).This subsystem is specifically designed forspecial intelligence communications.

Teletypewriter Subsystem. This subsystem is anextension of terrestr ial teletypewritertransmission networks.

Tactical Data Information Exchange Subsystem(TADIXS). This is a one-way broadcast oftactical information from command centersashore to afloat units primarily in support ofover-the-horizon targeting (OTH-T).

Officer in Tactical Command InformationExchange Subsystem (OTCIXS). T h i ssubsystem continues to provide inter-and intra-battle group communications and is now alsodesignated as the return path for ship-to-shoreOTH-T communications.

Demand Assigned Multiple Access (DAMA)Subsystem. This subsystem was designed tomultiplex several subsystems, or users, on onesatellite channel, allowing more satellitecircuits to use a single uhf satellite channel.

Control Subsystem. This subsystem is acommunications network that provides statusreporting and management of system assets

The instal lat ion of subsystem basebandequipment and rf terminals aboard ships is driven bycommunications traffic levels, type of com-munications, and mission requirements. For example,Fleet Broadcast, a common subsystem in naval com-munications, is received by many different types ofships. Atypical suite on a large ship may include FleetBroadcast, CUDIXS, NAVMACS, Secure Voice,TADIXS, OTCIXS, Teletypewriter, and TACINTELequipment.

Most subsystems have very rigid control andaccountability of message and data-link traffic. Allsubsystems have some form of backup mode. Withinthe constraints of equipment capability, eachsubsystem addresses the unique requirements of theuser and the environment in which the user operates.On board your ship, you may not use all these systems,but during your career you will probably come acrossall of them. Now that we have identified the satellitecommunications subsystems, we need to provide you

with a basic understanding of how they operate. Butfirst, we need to discuss FLTSATCOM ShorebasedTerminals.

FLTSATCOM SHOREBASED TERMINALS

SATCOM installations at shore terminals operatefrom existing naval communications centers andcertain command operations centers. Four NavalComputer and Telecommunications Area MasterStations (NCTAMS) have primary responsibility fornaval communications via satellite. They are:

NCTAMS LANT, Norfolk, Virginia

NCTAMS MED, Naples, Italy

NCTAMS WESTPAC, Finegayan, Guam

NCTAMS EASTPAC, Wahiawa, Hawaii

The Naval Computer and TelecommunicationsStation (NCTS), San Diego, California, as part ofTADIXS, provides connectivity between NCTAMSEASTPAC and NCTAMS LANT.

Ten NCTSs are used to retransmit Fleet Broadcastmessage traffic via hf links. In addition, an rf terminalat Yokosuka, Japan, transmits SSIXS and SecureVoice communications to the western Pacific andIndian Oceans. Also, there is landline connectionbetween Japan and NCTAMS WESTPAC to supportTADIXS and OTCIXS transmissions.

Within these facilities, each subsystem consists oftwo parts: the baseband equipment (used to collect andcontrol the transmitted or received communications)and the rf terminal (used by the baseband system totransmit and receive via satellite link). Somesubsystems have the baseband equipment and rfterminals in the same building, while others have thebaseband equipment installed at a remote facilitylocated some distance from the rf terminal. Mostsubsystems use a common rf terminal. However, theFleet Broadcast has an rf terminal specificallydesigned for that subsystem.

FLEET SATELLITE BROADCASTSUBSYSTEM

The Fleet Satellite Broadcast Subsystemprovides the capability to transmit Fleet Broadcastmessage traffic in a high-level jamming en-vironment. The subsystem has 15 subchannels ofencrypted message traffic at an input data rate of 75bps per channel. These subchannels are time-

division multiplexed and are transmitted in a one-way rf transmission at 1200 bps. The shore terminaltransmits this data on a direct-sequence, spread-spectrum shf signal to the satellite, where the signalis translated to uhf and down-linked to thesubscriber. Figure 3-2 shows a block diagram of theFleet Satellite Broadcast Subsystem.

The High-Speed Fleet Broadcast (HSFB) is aplanned upgrade to the Fleet Satellite BroadcastSubsystem. This upgrade will improve broadcasttransmission speed, information through-put (capabil-ity of equipment to process or transmit data during aspecific period of time), and flexibility.

Message Traffic Input

The Fleet Satellite Broadcast message traffic isqueued and/or channel selected by two processor-controlled message switching systems beforetransmission. These systems are the Naval Com-munications Processing and Routing System(NAVCOMPARS) for general service messagetraffic, and STREAMLINER for special intelligencemessage traffic. Fleet weather data from NavalOceanographic Command Centers is also transmittedon nonprocessor controlled channels.

Rf Transmission

The FLTSATCOM satellites have two rf channelsallocated for Fleet Satellite Broadcast message traffic.The primary channel is configured for an shf uplink tothe satellite and for translation within the satellite fortransmission as uhf in the downlink. The second rfchannel is designed for backup use only.

Since two channels are available, and severaldifferent modulation techniques are used for theuplink, there are seven different modes in which the rflink can be transmitted.

In modes 1 through 6, the shf transmissions aremade by the Satellite Communications TerminalAN/FSC-79. Mode 7 operates the rf uplink anddownlink at ultra-high frequencies and uses the uhftransceiver AN/WSC-5(V).

Reception

Subscribers receive the uhf downlink signalthrough the AN/SSR-1 receiver system, whichdemodulates and demultiplexes the signal. Thedemuxed signal is decrypted and read into the

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NAVMACS and TACINTEL processors for messagescreening and printing. (Refer to the discussion ofthese two systems.) Weather data is sent directly toprinters after decryption. Ships not equipped with oneor both of these systems will normally output thebroadcast to teletypewriters.

Fleet Broadcast Retransmission

At selected shore stations, fleet Broadcastmessage traffic is retransmitted on hf links. Thesestations receive the tdm data directly via cable orsatellite.

CUDIXS/NAVMACS

The CUDIXS subsystem is a shorebased in-stallation of processors and peripheral equipment thatprovides K link control of the network and processingat shore installations. Figure 3-3 shows a typicalCUDIXS installation.

NAVMACS is a shipboard message processingsystem that automatically guards a minimum of fourbroadcast channels, serves as an automatedshipboard terminal for CUDIXS, and providesaccountability for all incoming and outgoingmessage processing needs for ships of the fleet.

NAVMACS subscriber terminal equipment is similar toCUDIXS terminal equipment.

The NAVMACS program is designed to addressthe growth requirements in existing installations andthe unique requirements of ships having a high volumeof message traffic. In ships that have a message pro-cessing and distribution system (MPDS), t h eNAVMACS processor interacts with the MPDS pro-cessor. A basic NAVMACS system is shown in fig-ure 3-4.

NAVMACS reads the headings of incomingmessage traffic and separates all messages addressedto the ship or commands for which it is guarding. Thesystem compares every addressee on each incomingfirst run message against entries in its command guardlist (CGL). When the system finds one or morematches between addresses on the first run messageand the entries of the CGL, the message is printed(copied) onto a line printer. If an emergency or Flashprecedence message on a first run is received, it isprinted completely, regardless of whether or not amatch is found. For nonmatches of messages withprecedence lower than Flash, only the heading of themessage is printed.

Together, CUDIXS and NAVMACS provideimproved ship-to-shore and shore-to-ship operational

Figure 3-3.—CUDIXS equipment configuration.

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Figure 3-4.—NAVMACS (V) communications interface.

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communications. These improvements help increasemessage traffic through-put rates and traffic volume,and improve link reliability. Figure 3-5 shows bothsides of the CUDIXS/NAVMACS subsystem.

Message Traffic Input

At shore facilities, the primary collection pointfor message traffic to be transmitted or received onthe CUDIXS/NAVMACS r f l ink i s NAV-

SUBMARINE SATELLITEINFORMATION EXCHANGESUBSYSTEM (NON-DAMA)

SSIXS was designed to compliment vlf and mf/hfcommunication links between shorebased submarinebroadcast control authorities (BCAs) and submarines.Figure 3-6 shows a SSIXS subsystem.

This subsystem provides the submarinecommander the ability to receive messages transmittedvia satellite at scheduled intervals ( “ G r o u pBroadcasts”) . Between Group Broadcas t s ,submarines may transmit messages to the BCA,including a request for messages held in queue. Theshore terminal responds with acknowledgements forthe received messages and transmits all messagesaddressed to that particular submarine. Two modes,Group Broadcast and Query/Response, permit thesubmarine to be active or passive, depending on whatthe submarine commander wants. One 25-kHzwideband channel on each of the four FLTSATCOMsatellites has been allotted to SSIXS. A single SSIXSnetwork may have up to 120 submarine subscribers.

COMPARS.

Rf transmission Link Control (Non-DAMA)

The CUDIXS baseband equipment shares acommon rf terminal with other subsystems. At theshore facilities this terminal is a uhf transceiver,AN/WSC-5(V). Aboard ship, NAVMACS uses a uhftransceiver, AN/WSC-3(V). All uhf satellites have 25-kHz-wide channels allocated for CUDIXS/NAVMACS transmissions. Each channel is operatedas a half-duplex uhf link, with a data transmission rateof 2400 bps. The rf modulation is differential encodedphase-shift keying (DPSK).

Figure 3-6.—SSIXS subsystem.

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SECURE VOICE SUBSYSTEMSSIXS has undergone an upgrade (SSIXS II) thatreplaces the SSIXS shore equipment with newcomputer equipment.

Message Traffic Input

At the broadcast control authority (BCA), theconsole keyboard operator, high-speed paper tapereader, or Submarine Message Automated RoutingTerminal (SMART) enters into the SSIXS shoreterminal messages addressed to submarines that havebeen received from AUTODIN, NAVCOMPARS, orlocally over the counter in the message center. Aboardthe submarine, message traffic is input via theteletypewriter or tape reader equipment. SSNsubmarines that have the Data Link Control System(DLCS) installed have an additional input/outputcapability via the sensor interface unit (SIU) for over-the horizon targeting (OTH-T messages.

Rf Transmission Link Control

Ashore, the SSIXS subsystem shares access to thesame satellite rf terminal equipment as the other uhfSATCOM subsystems, with the exception ofCOMSUBGRU SEVEN, Yokosuka, Japan, which isequipped with dedicated AN/WSC-3 transceivers.

Since each BCA is located some distance awayfrom the Naval Computer and TelecommunicationsArea Master Station (NCTAMS), line modems andland lines are required for interconnection. Thesubmarine uhf rf terminal is the single-channel, half-duplex AN/WSC-3. SSIXS transmissions are at 4800bps. The capability to operate SSIXS in the DAMA net(see the section on DAMA) has been successfullydemonstrated and will be used in the future. Eachsubscriber to a SSIXS network is assigned a uniqueidentification number that is used in all transmissionsto or from the subscriber. The identification numbersare stored within the shore station and subscriberprocessors and are used for the following purposes:

At the shore stations, the subscriber iden-tification number, when combined with broadcasts,determines the number of times message traffic istransmitted to the subscriber.

When a subscriber makes a transmission to theshore station, the identification number is included. Theshore station will not acknowledge a transmissionwithout receiving the identification number.

The subscriber uses the number to screenincoming message traffic. Any data that is notaddressed to that particular subscriber is discarded.

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The Secure Voice subsystem enables thetransmission of ship-to-ship, ship-to-shore, and shore-to-ship voice communications via satellite relay.Figure 3-7 shows a Secure Voice subsystem.(AUTOSEVOCOM has been replaced by radiowireline interface (RWI) at all NCTAMS shoreactivities.) The subsystem transmits and/or receivessecure voice communications via a half-duplex, push-to-talk satellite link. Channels on each of the fourFLTSATCOM satellites have been allocated for use bythe Secure Voice subsystem. Control of the voicechannels is maintained by the Secure Voice controllerat the responsible NCTAMS/ NCTS.

The subsystem uses digitized voice at a data ratelow enough to be compatible with a 3-kHz voicechannel and is considered narrowband. The sound ofNarrowband Secure Voice is very distinctive. Onceyou hear it, you won’t forget it. The system uses specialanalog-to-digital processing of the speech signal at thehandset terminal and the rf transmission rate is 2400bps.

The Secure Voice subsystem has dedicated rfchannels on the uhf SATCOM satellites as well asdedicated DAMA time slots where DAMA nets havebeen established.

Voice Transmission

The rf terminal installations on mobile platformsdetermine the manner in which a Secure Voicetransmission is made. These mobile platforms maybecategorized into two types:

The small ship/submarine that share a single-channel AN/WSC-3(V) uhf transceiver andcryptographic equipment between NAVMACS orSSIXS and a Secure Voice terminal.

Larger ships that have two or more AN/ WSC-3(V) uhf transceivers and cryptographic equipment areinstalled. This installation normally has a transceiverdedicated to Secure Voice.

Secure Voice use is accomplished by either of twomethods. In the first method, ships access a SecureVoice channel if the channel is not in use. The shipcontacts another ship directly by using the availablechannel. When coordination of voice communicationswith shore commands is required, the ship contacts thevoice controller who, in turn, tells the recipient(s) of anincoming voice transmission.

Figure 3-7.—Secure Voice subsystem.

The second method requires a different processand is used if the channels are busy or if proceduresrequire this method. For the small ship or submarine, avoice transmission request must be sent by message tothe Secure Voice controller. A small ship uses theCUDIXS/NAVMACS network for the message. Thesubmarine may transmit a voice-channel requestduring a random-access time period in the SSIXS. Inboth cases, the request is passed from the receptionpoint ashore to the voice controller. The voice

controller coordinates the voice transmission byassigning a voice channel, contacting the unit that willreceive the voice transmission, and following throughwith the transmission.

Radio Wireline Interface

The Radio Wireline Interface (RWI) w a sdeveloped to access and interconnect existing andfuture Secure Voice subsystems and equipment. It pro-vides the capability to connect shorebased worldwide

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terrestrial (wireline) systems with the SATCOM,Defense Satellite Communications Systems, andalternate hf systems. This system extends shorecommunications seaward and gives commands at seathe same Secure Voice telephone communicationscurrently provided to the worldwide shore es-tablishment. The RWI provides interconnectionamong the Secure Voice Improvement Program(SVIP) channels (STU-III units), a RED telephonebus, the Advanced Narrowband Digital VoiceTerminal, SATCOM radio terminals (uhf, shf, and inthe future, ehf), and hf radio links.

TACTICAL INTELLIGENCE SUBSYSTEM

The Tactical Intelligence subsystem (TACINTEL)is used to transmit special-intelligence communica-tions. A link-control protocol has been adapted to a for-mat required for communication across a DAMA-supported channel using a polling scheme that can sup-port a net membership of 23 subscribers. A portion of aDAMA 25-kHz channel on each of the FLTSATCOMsatellites has been allocated for TACINTEL. A TACIN-TEL subsystem is shown in figure 3-8.

TACINTEL also processes time-sensitive sensordata and other data essential to Indications andWarnings and OTH-Targeting. In addition, thissystem, unlike CUDIXS/NAVMACS, can be used fordirect ship-to-ship interchange of this data.

Rf Transmission

TACINTEL baseband equipment uses an rfterminal in common with other subsystems at bothshore facilities and subscriber terminals. Shorefacilities use an AN/WSC-5(V); subscribers use an

AN/WSC-3(V). The TACINTEL channel operates as ahalf-duplex uhf link at 1200, 2400, or 4800 bps.Modulation is DPSK

Subscriber Reception

Each subscriber has an identification numberrecognized by the subscriber processor. This numberserves as the initial basis for incoming messagescreening. Screened message traffic is sent to theTACINTEL peripheral equipment (printer) or theinterfacing systems. The remaining message traffic isdiscarded without release.

Future TACINTEL

The TACINTEL II program will upgrade theexisting TACINTEL and incorporate state-of-the-arthardware and software. It will be a computer-basedmessage communications system, enabling automaticreceipt and transmission of Special Intelligencecommunications for both ashore and afloat users.During the transition, it will be compatible with thepresent TACINTEL.

TELETYPEWRITERSUBSYSTEM

The Teletypewriter Subsystem expands existingteletypewriter communications networks by usingsatellites as relay stations.

The Navy continues to have numerous uses for the75-bps tty. These include dedicated full-timeterminations for beyond-line-of-sight tactical andreport-back circuits and as backup connectivity forne tworks such as CUDIXS/NAVMACS andTACINTEL. A non-DAMA-configured teletypewritersubsystem is shown in figure 3-9.

Figure 3-9.—Teletypewriter subsystem-non DAMA.

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TADIXS/OTCIXS

TADIXS supports the exchange of Over-the-Horizon Targeting (OTH-T) information betweenshore and fleet-based computer systems that supportNavy cruise missile operations. Surface ships andsubmarines operate in a TADIXS receive-only mode.OTH-T data from the fleet destined for shore orother fleet users is sent by the afloat Tactical DataProcessors (TDPs) through the TADIXS ON-143(V)6/USQ to the OTCIXS ON-143 (V)6/USQ

for transmission over the OTCIXS satellite. ATADIXS surface ship installation is shown in figure3-10. Each OTCIXS-equipped surface ship orsubmarine can enter both out-going teletype andTDP traffic simultaneously.

Rf Transmission Link Control

The TADIXS satellite link network operates in ahalf-duplex manner at a data rate of 2400 bps in apermanently assigned time slot of a uhf DAMAchannel. Control of message traffic transmission is

Figure 3-10.—TADIXS surface ship installation.

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achieved by a polling and controlled access protocolinstalled in the TADIXS radio controller (shore)software and the TADIXS satellite link controller(afloat) software.

In the non-DAMA mode, OTCIXS operates in ahalf-duplex manner at a data rate of 2400 bps using adedicated uhf channel. When functioning in theDAMA mode, OTCIXS operates at a data rate of 1200or 2400 bps in a permanently assigned time slot of a uhfDAMA channel. Control of message traffictransmission is achieved by a demand-assigned accessprotocol installed in the OTCIXS radio controller(shore) and satellite link controller (afloat) software.

Message Traffic Reception

Each subscriber in the TADIXS network has aunique identification number recognized by thesubscriber processor. This number serves as the initialbasis for incoming message traffic screening.TADIXS or OTCIXS satellite link controllers (onafloat units) compare redundant receptions foraccuracy and form the most accurate composite of thetraffic received.

For surface ship and submarine users, screenedmessage traffic is sent to the teletypewriter or TDPsystem, as applicable. The rest of the traffic isdiscarded. The reception of traffic does not make thesatellite link controller send an acknowledgement.This allows afloat platforms to receive traffic whileoperating in an emission control (EMCON) en-vironment.

DEMAND-ASSIGNED MULTIPLE ACCESS(DAMA) SUBSYSTEM

The uhf DAMA subsystem was developed tomultiplex several baseband systems or users on one25-kHz satellite channel. This had the effect of addingmore satellite circuits per channel to the uhf SatelliteCommunications System. Without uhf DAMA, eachsatellite communications subsystem requires aseparate satellite channel.

DAMA equipment accepts encrypted data streamsfrom independent baseband sources and combinesthem into one continuous serial output data stream.DAMA interfaces the Navy uhf SATCOM subsystemsand the AN/WSC-5(V) and DAMA-compatibleAN/WSC-3(V) transceivers. The DAMA unit (TD-1271B/U multiplexer) includes a modem, eliminatingthe need to use a separate modem at the AN/WSC-5(V)or the modem within the AN/WSC-3(V). Thebaseband equipment input or output (I/O) data rate

with DAMA equipment can be 75, 300, 600, 1200,2400, 4800, or 16,000 bps. The DAMA transmissionrate on the satellite link (burst rate) can be 2400,9600,19,200, or 32,000 symbols per second (sps).CUDIXS/NAVMACS, Secure Voice, and OTCIXScurrently use 2400 bps. TACINTEL operates at 2400or 4800 bps, depending upon the ocean area.

The DAMA multiplexed data stream is divided intoframes, with each frame being 1,386 seconds long. Eachframe is subdivided into time slots as shown in figure3-11. Most of the DAMA frame formats are derivedfrom this basic format. In the following paragraphs, wewill name and describe the purpose of each slot.

Channel Control Order Wire (CCOW) Slot

This slot is used to transmit system timing andcontrol information from the channel controller tosubscriber units only. It provides subscriber units withsystem timing, configuration, and satellite rf controlinformation. It occurs at the beginning of each frame.

Return Channel Control Order Wire(RCCOW) Slot

This time slot provides limited order wirecapability for DAMA-related subscriber-to-channelcontroller communications. It is used for transmissionfrom the subscriber to the channel controller.

Ranging Time Slot

This is the time slot during which the user’sTD-1271B/U determines the range between the userterminal and the satellite to set the transmitter syn-chronization required for timing. All DAMA multi-plexer transmit times are referenced to the satellite.

Link Test Slot

The link test slot is used to evaluate theperformance of the satellite link. Each subscriber isable to transmit a fixed data stream through thesatellite, receive that bit stream, and then perform erroranalysis automatically.

Figure 3-11.—Basic DAMA frame format.

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Data Time Slots

These are the time slots during which userstransmit or receive data. There are three segments oftime slots in each frame, designated A, B, and C.Segment A may contain from one to five circuits; Bmay contain from one to eleven circuits; and C maycontain from one to six circuits. The number of circuitsin each group depends on the baseband data rate, theforward correction rate, and the transmission burstrate, as influenced by the radio frequency interference(RFI) environment.

Current Operation

For communications on the eastern Pacificsatellite, a master control station is installed atNCTAMS EASTPAC. This same pattern of DAMAequipment installations has been followed atNCTAMS LANT, MED, WESTPAC, and NTCS.Each master control station has multiple multiplexerinstalled, and each TD-1271B/U multiplexer canaccommodate up to four circuits. The number ofmultiplexer installed aboard each ship variesaccording to platform requirements.

Any DAMA-equipped platform with full-duplexcapability can be designated a channel controller. Thiscapability provides an emergency backup for theshorebased master controller terminals. A DAMAsubscriber who is designated a channel controller willprovide all the required CCOW functions for DAMAsystem control of a particular rf channel.

Operationally, the user terminal will have itsbaseband port automatically connected to a data timeslot when the proper slot number is keyed into themultiplexer front panel keyboard. Each SATCOMsubsystem that uses DAMA will have a specific slotnumber. Circuits will normally be operated on a nettedbasis, and circuit numbers will be assigned byCOMNAVTELCOM and/or FLTCINC.

Transition

Transition to DAMA is taking place in a mannerthat allows subscribers converted to DAMA tocommunicate with those who have not been converted.During the transition period, equipment installedat shorebased master stations will form gatewaysbetween DAMA and non-DAMA circuits. In thefollowing paragraphs, we will discuss subsystems thatare either currently undergoing conversion to DAMA

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or are planned for conversion, so you will know what toexpect in the future.

Secure Voice —DAMA is now being phased intothe Secure Voice Subsystem. A DAMA-configuredSecure Voice Subsystem is shown in figure 3-12.

CUDIXS/NAVMACS —NAVMACS platformswill be gradually transitioned to DAMA. Thistransition will start when CUDIXS shore andCUDIXS/NAVMACS ship hardware and softwarehave been modified for compatibility with DAMA. Atthat time, a transition will begin allowing DAMA ornon-DAMA ships to communicate with the CUDIXSshore terminal. A DAMA-configured CUDIXS/NAVMACS subsystem is shown in figure 3-13.

Teletypewriter —Teletypewriter capability viaDAMA becomes available as DAMA is installed oneach platform. To provide maximum flexibility duringthe transition, capability is provided at the shorebasedmaster control stations to interface non-DAMA andDAMA users. Figure 3-14 shows a DAMA-configuredteletypewriter subsystem.

CONTROL SUBSYSTEM

The Control Subsystem is structured to performthe following tasks:

Sense and collect system status information in adefined geographical area and on a worldwidescale.

Control system resources and the degradationof system capability.

The Control Subsystem is a combination of severalareas and levels of command. The major players arelisted below:

The Chief of Naval Operations is the executiveauthority for all SATCOM system.

The Commander, Naval Space Command isresponsible for the operational control and managementof these systems and for the effective operation andmaintenance of assigned Navy resources for theDepartment of Defense.

The Naval Computer and TelecommunicationsCommand performs the required functions to pro-vide day-to-day control and operation of naval satellitecommunications assets. With coordination, systemresources can be adjusted to meet operational needs.

Figure 3-12.—DAMA-configured Secure Voice Subsystem.

Supporting the control subsystem are NCTAMS,NCTS, the USAF Satellite Operations Center, andcontractor-operated control facilities.

The key to controllability lies in having manypoints for sensing the status of subsystems andequipment operation. Status data may be collected byoperators or by special facilities or equipment. Thereare many points within each subsystem wheresubsystem and equipment operational status is

collected. Also, several subsystems/systems have theability to provide a printout of status information.

Transmission of status data from the NCTAMS,NCTS, and USAF Satellite Operations Center is viateletypewriter order wire. The Naval Computer andTelecommunications Command maintains asubstantial quantity of updated status data in computerfiles. A diagram of the Control Subsystem is shown infigure 3-15.

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Figure 3-14.—DAMA-configured teletypewriter subsystem.

Figure 3-15.—Contro1 Subsystem functional diagram.

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SATELLITES

In 1976, three satellites were placed into orbit overthe Atlantic, Pacific, and Indian Oceans. Thesesatellites, called MARISATs, were procured by andare managed by the COMSAT General Corporation.Each satellite has three uhf channels for military use(one wideband 500-kHz channel and two narrowband25-kHz channels). The uhf section of each satellite isleased to the Navy for communications. To distinguishthe special management and control functions forcommunications on these uhf channels, the Navy hasgiven the leased MARISAT satellite assets the nameGAPFILLER.

Current planning calls for no Navy use ofGAPFILLER satellites after the mid-1990’s. Satellitecoverage will then be provided by a combination ofF L T S A T and L E A S A T until the new U H FFOLLOW-ON (UFO) satellites are placed intoservice. The Navy plans to have two operationalsatellites in each of four satellite coverage areas. Eachsatellite coverage area can be terminated in at least twoNCTAMS, allowing around-the-world connectivity.You can see this connectivity in figure 3-16.

FLTSATCOM SATELLITE

The FLTSATCOM satellite consists of two majorparts: a payload module that includes the antennas anda space craft module with a solar array. The payloadmodule contains the uhf, shf, and S-band (tracking,telemetry, and command) communications equipmentantennas. The communications equipment is mountedinternally on side panels that cover this section of thesatellite.

The space craft module contains nearly all othersubsystem equipment, including sensors, attitude andvelocity control, telemetry, tracking and command,and electrical power distribution. The spacecraft isstabilized on three axes, and the body-fixed antennasare kept pointing at the sun by a clock drive. AFLTSATCOM satellite is shown in figure 3-17.

E a c h F L T S A T C O M s a t e l l i t e c a n r e l a ycommunications on 23 separate uhf channels. Of the23 channels, 10 are 25-kHz channels, 12 are 5-kHzchannels, and one is a 500-kHz channel. The ten 25-kHz channels are dedicated for Navy use. Each 25-kHzuhf down-link channel has a separate transmitter.Channel one, used in primary mode for Fleet Broadcasttransmissions, incorporates signal processing withinthe satellite (the shf up-link signal is translated to uhf

Figure 3-17.—FLTSATCOM satellite.

for down-link transmission). In addition, two of theFLTSATCOM satellites have ehf packages attached.

FLTSAT Extremely-High-Frequency Package(FEP)

The Fleet Satellite (FLTSAT) Extremely-High-Frequency (EHF) Package (FEP) provides ehfcommunications capability for Army, Navy, and AirForce ground, airborne, and ocean-going terminals.Two FEPs are currently in orbit, carried aboard twomodified uhf FLTSATs, numbers seven and eight.

FEP operates at ehf frequencies of approximately20-GHz on the down-link and 44-GHz on the up-link.It has two antenna beams: (1) a dual-frequency spotbeam steerable by ground command, and (2) an earthcoverage beam that uses separate horn antennas fortransmit and receive.

LEASAT SATELLITE

The LEASAT satellite has seven 25-kHz uhfdown-link channels, one 500-kHz wide-band channel,and five 5-kHz channels. One of the seven 25-kHzdown-link channels is used for Fleet Broadcast.The broadcast up-link is shf, with translation touhf taking place in the satellite. The remaining

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six channels function as direct relay channels withseparate repeaters. A LEASAT satellite is shown infigure 3-18.

Compared to FLSATCOM satellites, LEASATsatellites have a reduced number of 25-kHz channels.However, they can still serve expanding NavySATCOM requirements by using the groundbasedDAMA technique, effectively using each satellitechannel more efficiently.

UHF FOLLOW-ON SATELLITE

The purpose of the Ultra-High-Frequency Follow-On Satellite System (UHF F/O) is to provide satellitecommunications for DOD and other governmentagencies through satellites in geosynchronous orbit.The current satellites, GAPFILLER, FLTSATCOM,and LEASAT are approaching the end of their normalmission life. UHF F/O will provide the neededreplenishment satellites. The strategy for replacementis to use existing FLTSATCOM and LEASAT assetsfully, while deploying the UHF F/O satellites tominimize communications disruptions as theFLTSATCOM and LEASAT satellites fail or reach theend of their useful life. An exploded view of a UHFF/O satellite is shown in figure 3-19.

Communications Capability

The uhf communications subsystem consists ofreceive and transmit antennas, a low-noise pre-amplifier, 25- and 5-kHz channel receivers and

Figure 3-18.—LEASAT satellite.

transmitters, and an output multiplexer. The shfcommunications subsystem provides shf anti-jam up-link capability for Fleet Broadcast (which is down-linked as uhf) and consists of receive and transmitantennas, the receiver, a dual channel processor, andthe beacon transmitter. Signals received by the shfreceive antenna are fed to the shf receiver. In turn, theprocessor provides Fleet Broadcast outputs that are fedto uhf communications subsystem for down-link. Themultiplexed anti-jam broadcast capability of the UHFF/O permits up to three broadcast channels to be up-linked and down-linked simultaneously.

On the fourth and subsequent satellites deployed,an ehf communications subsystem will provide threeehf broadcast channel up-links and seven ehfcommunications channel up-links. Each of these ehfup-links will be capable of being down-linked as ehfonly, uhf only, or simultaneously as uhf and ehf. UHFF/O will also have the capability of transmitting andreceiving ehf telemetry and command data.

User interfaces for UHF F/O are identical to thoseof the current FLTSATCOM and LEASAT constella-tion. The uhf portion of the UHF F/O system iscompatible with all existing Navy uhf terminals exceptthose using frequency-hopping techniques.

Channel Allocations

The UHF F/O satellite channels are allocated andgrouped as follows:

Group I has a single 25-kHz bandwidth channelwith a variable satellite translation frequency and a jamresistant shf up-link.

Group II has nine 25-kHz bandwidth channelswith a satellite translation frequency of 41 MHz.

Group III has eight 25-kHz bandwidth channelswith a satellite translation frequency of 33.6 MHz.

Group IV has eight 5-kHz bandwidth channelswith a satellite translation frequency of 73.1 MHz.

Group V has thirteen 5-kHz bandwidth channelswith a satellite translation frequency of 53.6 MHz.

MILSTAR

MILSTAR is a new generation Satell i teCommunications (SATCOM) system being developedby the Navy, Army, and Air Force for two primarypurposes. First, it will provide a survivable

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Figure 3-19.—UHF Follow-On satellite exploded view.

communications capability to the National CommandAuthority (NCA). Second, it will provide sufficientcommunications support for both strategic and tacticalmissions. The primary objective of the MILSTARprogram is to develop and deploy an affordable, jam-resistant SATCOM system that will meet both long-haul and local communications needs.

MILSTAR will use communications terminalsthat will provide Secure Voice (SV), Teletype (TTY),data, and facsimile EHF SATCOM. MILSTARterminals will be installed on aircraft, in fixedtelecommunications centers, landbased tacticalelements, shorebased telecommunications centers,surface ships, and submarines.

In the following paragraphs, we will look at someof the equipment associated with satellite com-munications.

SATELLITE EQUIPMENT

The equipment used in Navy SATCOM sub-systems can be divided into two general groups, rfterminals and the baseband equipment common to aprocessor installation. The selection of specificequipment is determined by the operating en-

vironment—whether installation is to be aboard a ship,submarine, aircraft, or shore installation. In thischapter, we will limit our discussion primarily tocommonly used shipboard and shore equipment.

Satellite Communications TerminalAN/FSC-79

The AN/FSC-79 terminal processes and converts70-MHz signals to X-band (shf) transmitted signals. Italso converts received signals from X-band to 70 MHz.This terminal can simultaneously transmit a spreadspectrum carrier and receive a satellite beacon signal.The design of the terminal provides redundancy inmany components to ensure a high degree ofavailability. The terminals are installed at NCTAMSLANT, MED, WESTPAC, EASTPAC, and NCTS,Stockton (contractor operated).

Uhf Transceiver AN/WSC-5(V)

The AN/WSC-5(V) transceiver provides aneight-circuit, full-duplex data operation or, as analternative, six full-duplex data circuits and twoFM audio or tone-group circuits. It also providesan interface for connectivity to the uhf DAMA

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Figure 3-20.—Uhf transceiver AN/WSC-5(V).

equipment. Figure 3-20 shows an AN/WSC-5(V)transceiver installation.

This transceiver is capable of three types ofmodulation/demodulation:

• Frequency modulation/demodulation with pre-emphasis/ de-emphasis for voice transmission/ reception.

• Frequency modulation/demodulation without pre-emphasis/de-emphasis for tone-group transmission/reception.

• Differentially encoded phase-shift keying using theOM-43A/USC modem. The transceiver has a 70-MHzinterface for connection to either the modem or the TD-1271B/U DAMA multiplexer.

All four NCTAMS have AN/WSC-5(V)transceivers installed.

The C-11330/WSC-5(V) shown in figure 3-21provides for remote control of the AN/WSC-5(V) forteletype operation. The C-11330/WSC-5(V) is similar tothe C-9899/WSC-3, except that it uses +6 Vdc for the

keyline signal and indicator lamps. Both units haveidentical front panels.

Transceiver AN/WSC-3(V)

To be consistent in this discussion, we will refer toboth the AN/WSC-3 and AN/WSC-3(V) transceivers

Figure 3-21.—Control-Indicator C-11330/WSC-5(V)or C-9899/WSC- 3.

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Figure 3-22.—Uhf radio RT-1107/WSC-3.

as AN/WSC-3. A single AN/WSC-3 (RT-1107/WSC-3)is shown in figure 3-22.

The AN/WSC-3 transceiver is used primarilyaboard ship, at Marine Corps terminals, and at selectedshore installations. It has various configurationsdesigned to meet the particular requirements of theseplatforms. The configuration differences are identified inthe AN/WSC-3 variations table, table 3-1.

The transceiver can be operated in either satellite orline-of-sight mode, either locally or remotely. Amodulation control permits selection of PSK data ratesfrom 75 to 9600 bps, FSK modulation at 75 bps, and FMor AM modulation for voice. The rf output is 30 wattsAM and 100 watts for FM, PSK, and FSK

The AN/WSC-3A, AN/WSC-3A(V)2 and (V)3have been modified for use with the DAMA subsystem.The AN/WSC-3(V)15, (V)17, and (V)19 aremanufactured as DAMA-capable.

The transceiver has two control indicators forremote operations. The C-9351/WSC-3, shown in figure3-23, provides for remote control of the AN/WSC-3 asdescribed in the table 3-1 description. As we mentionedbefore, the C-9899/WSC-3 provides for remote teletypeoperation. Two built-in modems are included with thetransceiver.

Receiver Systems AN/SSR-1 and 1A

You have probably seen this receiver since it is installedaboard most naval surface vessels. It enables ships to receiveFleet Satellite Broadcast. The received carrier may containeither FM or PSK modulation; the preferred demodulation isselected manually with a switch associated with thereceiving set. The AN/SSR-1 can drive high-level teletypeequipment. The AN/SSR-1A can drive both high- and

Figure 3-23.—Control-Indicator C-9351/WSC-3.

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Table 3-1.—AN/WSC—3 Variations

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Table 3-1.—AN/WSC—3 Variations—Continued

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low-level teletype equipment. A receive system is shown in figure 3-24.

Figure 3-24.—Typical receive-only system.

The receiver system includes up to four AS-2815/SSR-1 antennas with an Amplifier ConvertorAM/6534/SSR-1 (fig. 3-25). It also includes aCombiner-Demodulator MD-900/SSR-1 (fig. 3-26)and a Demultiplexer TD-1063/SSR-1 (fig. 3-27). Theantenna and convertors are mounted above deck inpositions that ensure that at least one antenna is alwaysin view of the satellite. The combiner-demodulator anddemultiplexer are mounted below deck.

The receiver accepts rf signals between 240 MHzand 340 MHz, a modulation bandwidth of 25 kHz. Thecombiner-demodulator demodulates the rf input fromthe amplifier convertor and provides a 1200-bps outputfor the demultiplexer. The demultiplexer accepts aninput of 1200 bps and outputs 15 channels at 75 bps.The decrypted demultiplexer output is patched toNAVMACS, TACINTEL processors, or tele-typewriters.

Antennas

SATCOM antennas will be discussed in volume 7of this training series.

Figure 3-25.—Receiving Antenna AS-2815/SSR-1 and AmplifierConverters AM-6534/SSR-1.

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Figure 3-26.—Combiner-Demodulator MD-900/SSR-1.

Figure 3-27.—Demu1tiplexer TD-1063/SSR-1.

Modem Group OM-43A/USC

The OM-43A/USC shown in figure 3-28 is usedprimarily with the AN/WSC-5(V) transceiver at shoreinstallations. It performs differential phase-shift keying(DPSK) modulation and demodulation of a

Figure 3-28.—Modem Group OM-43A/USC.

serial data stream at data rates of 75, 300, 1200, 2400,4800, and 9600 bits per second. This modem can beoperated in fill-duplex, although normal operation is half-duplex.

Modulator-Demodulator OM-51A/FR

This modem is an integral part of the Fleet SatelliteBroadcast subsystem. It is a spread spectrum (widebandwidth with frequency modulation of a transmitter andreceiver in exact synchronization) type modem used withthe AN/FSC-79 satellite communications terminal toprovide rf transmission capability in a high-level jammingenvironment. Shown in figure 3-29, its basic function is toprovide rf analog and digital conditioning circuits andfrequency synthesizing for dual-redundant transmissionand reception. It interfaces with the AN/FSC-79 terminaland the AM-6534/ SSR-1 amplifier-convertor.

Figure 3-29.—Modulator-Demodulator Group OM-51A/FR.

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Figure 3-30.—Data Processing Set AN/UYK-20(V).

This installation consists of a standard cabinetcontaining seven assemblies: a summary controlpanel, frequency synthesizer, receiver-synchronizer,coder-modulator, demodulator, and two powersupplies.

Data Processing Set AN/UYK-20(V)

The AN/UYK-20(V), figure 3-30, is a general-purpose processor designed to meet the requirementsof small and medium processor applications inshipboard or shore military facilities. The processor isused in the CUDIXS, NAVMACS, SSIXS (shoreinstallations), and TACINTEL subsystems.

Data Processing Set AN/UYK-44(V)

The AN/UYK-44(V), figure 3-31, was designed tomeet the same requirements as the AN/UYK-20(V),and to use AN/UYK-20(V) software with minimummodifications. It is used in the TADIXS subsystem,

Figure 3-31.—Data Processing Set AN/UYK-44(V).

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Communication System Control CenterAN/USQ-64(V)

This control center is used to pass satellite datatraffic efficiently and bidirectionally between a ship andshore. It turns associated transmitters on and offaccording to a polling scheme. It also uses detection andcorrection and sends automatic requests forretransmission to improve received data accuracy. Theten AN/USQ-64(V) variations and their uses are asfollows:

• (V)l—SSIXS shore installations

• (V)2—CUDIXS shore installations

• (V)3—SSIXS subscriber installations

• (V)4—NAWCS shore installations

• (V)5—TACINTEL ship subscriber, for passingSpecial Intelligence (S1) data traffic bidirectionallybetween a NCTS and fleet nets

• (V)6—TACINTEL shore installations, for the samepurpose as (V)5

• (V)7—OTCIXS: fixed submarine or shipboardinstallations for passing TDP formatted data andteletypewriter traffic

• (V)8—TADIXS ship and submarine installations

• (V)9—TADIXS Gateway Facility (TGF)

• (V10)—Tactical Data Processor Controller

Interconnecting Group ON-143(V)/USQ

Each ON-143(V)/USQ configuration varies,depending on its particular use. It fits within limitedspaces aboard small ships and submarines, performing avariety of functions related to several input-outputchannels of the control processor. It provides red-blackisolation, synchronization of crypto units, levelconversions, and crypto test and alarm signals. It alsoprovides crypto control and interfaces baseband systemcomponents with rf link equipment. An ON-143(V)4/USQ is shown in figure 3-32.

Data Terminal Set AN/USQ-69(V)

The Data Terminal Set shown in figure 3-33 has a15-inch diagonal screen on which a 2000 character pagecan be displayed. The memory is available in two

Figure 3-32.—Interconnecting Group ON-143(V)4/USQ.

sizes, 2000 and 6000 characters. When memoryoverflows as a result of computer output, a computerinterrupt is initiated. Overflow as a result of operatorinput causes an audible alarm. This unit is currently usedwith TACINTEL (ship) and NAVMACS.

Figure 3-33.—Data Terminal Set AN/USQ-69(V).

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Signal Data Recorder-ReproducerRD-397( V)/U

The RD-397(V)/U, figure 3-34, is used in basebandequipment installations with CUDIXS, NAVMACS, andTACINTEL (ship and shore). The (V)3 version is used atSSIXS shore locations. This tape perforator/reader canpunch tape at 63.3 characters per second and read tape atup to 300 characters per second. The equipment is self-contained; that is, complete with control logic, buffering,and power supplies.

Navy Standard Teleprinter AN/UG C-143(V)

The Navy Standard Teleprinter (NST) is the standardteleprinter terminal set for surface platforms. The NST isused for netted circuits and for broadcast, ship-to-shore,and ship-to-ship communications circuits. The variousconfigurations of the NST provide for informationpreparation, editing, printing and receiving of serial data,and buffering and storage of information. An AN/UGC-143A(V) 4 NST is shown in figure 3-35.

Figure 3-34.—Signal Data Recorder-Reproducer RD-397( V)/U.

Figure 3-35.—NST AN/UGC-143(V).

Audio Digital Converter CV-3333/U

The Audio Digital Converter CV-3333/U is called avocoder or voice digitizer. This unit is a solid-state, all-digital speech processor, providing speech output at a datarate of 2400 bps. It is capable of fill- duplex or half-duplexoperation, figure 3-36. It can be used to provide a singledigitized voice circuit, or have its output multiplexed withother data-bit streams to provide simultaneous voice anddata transmission. It is used primarily as an analog-to-digital converter in Fleet Satellite Secure Voicecommunications.

Switching Unit SA-1704/UG

The Switching Unit SA-1704/UG is used in basebandequipment shore installations of SSIXS, CUDIXS, andTACINTEL subsystems. It is a passive patch panel thatshows the equipment configuration in use. Eachsubsystem unit is slightly diff erent. In CUDIXS, theswitching unit maybe used to switch in equipment fromthe spare system; whereas in SSIXS, it is used to switch instandby equipment. The SB-4333/U PatchingSwitchboard is the planned replacement for this unit.

Time-Division Multiplexer TD-1150/USC

The TD-1150/USC time-division multiplexer isinstalled at broadcast keying stations ashore. It is used inthe Fleet Satellite Broadcast subsystem and consists oftwo units, one online and the other in standby. It acceptsup to fift een 75-bps data channels and multiplexes thisinformation into a single 1200-bps output data stream. ATD-1150/USC is shown in figure 3-37.

Multi plexer (DAMA) TD-1271B/U

The Multi plexer (DAMA) TD-1271B/U is usedin the DAMA subsystem and provides time-division

Figure 3-36.—Audio Digital Converter CV-3333/U.

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Figure 3-37.—Time-Division Multiplexer TD-1150/USC.

multiplexing of several digital data sources over onesatellite channel. This allows platforms equipped withthe TD-1271B/U and proper RT equipment to time-share the satellite channel. Each multiplexer has fourI/O ports for connecting baseband equipment and fourremote request and status display units. The TD-1271 B/U interfaces with RT equipment on a 70-MHzIF. Outputs from the unit also control the frequencyand synchronize the transmit and receive timing of theradio. A TD-1271B/U is shown in figure 3-38.

Figure 3-39.—Multiplexer (Mini-DAMA) AN/USC-42(V)prototype.

Multiplexer (Mini-DAMA)AN/USC-42(V)1/(V)3

This unit is currently under development, withtechnical and operational evaluation to take placesoon. Mini-DAMA is compatible and interoperablewith the TD-1271B/U and will perform or eliminate allfunctions of the AN/WSC-3(V)2/(V)3. A Mini-DAMA unit is shown in figure 3-39.

Cryptographic Equipment

Several different models of cryptographicequipment are used in the FLTSATCOM system.

Figure 3-38.—Multiplexer (DAMA) TD-1271B/U.

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Check your command’s communications configurationfor identification of this equipment. Specific informationon this equipment is available on a need-to-know basis.

Electrical Equipment Rack CY-7597/WSC-3, CY-7597A/WSC-3

The CY-7597/WSC-3 (fig. 3-40) and CY-7597A/WSC-3 provide for mounting of one C-9597/WSC-1(V)antenna control, one C-10232/WSC-3, and up to fourRT-1107/WSC-3s. These racks contain all the wiringrequired to interconnect these items. Connectorsinstalled on the top panel provide system interfaceconnections for baseband, teletype, frequency standard,external modem, and control-indicator equipment.

The C-9597/WSC-1(V) antenna controller providesa means of controlling the antennas in the OE-82 dual-

Figure 3-40.—Electrical Equipment Rack CY-7597/WSC-3.

shipboard system. The control indicator 3-34 can switchthe AN/WSC-3s for LOS or SATCOM use, monitor rfoutput power, and provide power on/off switching.

Electrical Equipment CabinetCY-7971/WSC

The CY-7971/WSC (fig. 3-41), provides formounting one MX-10342/WSC, two SB-4124/WSCs,and two TD-1271B/U multiplexer. The cabinet containsall wiring required to interconnect these pieces ofequipment. Connectors installed on the top panel providesystem interface connections for baseband, teletype,frequency standard, AN/WSC-3, and control-indicatorequipment.

The MX-10342/WSC provides a means to monitorand test all functions. The SB-4124/WSCs are data-

Figure 3-41.—Electrical Equipment Cabinet CY-7971/WSC.

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Figure 3-42.—Control Monitor Group OK-481(V)2/FSC.

and control-patching switchboards. Since we discussedthe multiplexer in depth earlier, we will not go intodetail here.

Control Monitor Group OK-481(V)2/FSC

The Control Monitor Group OK-481(V)2/FSC is apart of the Navy uhf satellite communications system.

This group provides for the interfacing of the TD-1271B/U multiplexer, the AN/WSC-5(V), and thebaseband equipment used at DAMA shore installations.It provides for rapid reconfiguration and monitoring ofinterfaced equipment using digital, rf, and monitorpatching facilities. It can accommodate up to 14 TD-127lB/U’s and can multiplex up to 56 baseband circuits.An OK-48l(V)2/FSC is shown in figure 3-42.

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CHAPTER 4

THE LINK-11 SYSTEM

INTRODUCTION

Tactical data links are usually limited to a specific area of operation and are usedfor command and control of specific forces. Link-11 is the U.S. Navy shipboardversion of Tactical Data Information Link-A (TADIL A). The Link-11 system isused to provide high-speed, computer-to-computer exchange of digital tacticalinformation among ships, aircraft, and shore installations, as shown in figure 4-1.

Figure 4-1.—Tactica1 digital information links.

Link-11 data communications can operate with either high-frequency (HF) orultra-high-frequency (UHF) radios. In the HF band, Link-11 provides gaplessomnidirectional coverage of up to 300 nautical miles from the transmitting site. Inthe UHF band, the Link-11 system is capable of line-of-sight omnidirectionalcoverage, approximately 25 nautical miles between ships and 150 nautical miles forship-to-air links.

To understand the operation of the Link-11 system fully, you must be able toidentify the hardware components that compose it and the functions they perform.

4-1

After completing this chapter you should be able to:

Describe the composition of a typical Link-11 system.

Describe the operation of the Link-11 transmission and receive cycles.

Describe the six operating modes of the Link-11 system.

Describe the function of the Link-11 encryption (security) device.

Describe the audio tones generated by the Link-11 Data Terminal Set.

Describe the word formats used to transmit Link-11 tactical data.

Describe the message formats used in the various Link-11 operatingmodes.

Describe the Operation of the Link-11 Data Terminal Set.

LINK-11 FUNDAMENTALS antenna coupler, and an antenna. The data terminalset is the center of the Link-11 system and is covered

To monitor the operat ion of and perform in detail later in this chapter. The communicationsmaintenance on the Link-11 system, you must switchboard is used to select the desired HF or UHFunderstand how the different pieces of equipment transceiver. An external frequency standard is alsointeract with each other. Let’s take a look at a basic part of many Link-11 systems. Additionally, theLink-11 system. Shipboard Gridlock System (SGS) is installed on

many ships. On SGS-equipped ships, an AN/UYK-20LINK-11 SYSTEM OVERVIEW is placed in the line between the CDS computer and

the crypto device.A typical shipboard Link-11 communications

system (figure 4-2) and consists of the following CDS Computerc o m p o n e n t s : t h e C D S d i g i t a l c o m p u t e r , acryptographic device, the Link-11 data terminal set, The central processor of the Combat Directionthe communications switchboard, and the HF or UHF System is the CDS computer. Keeping a data base ofradio set transceivers (transmitter-receiver), an tracks is among the many functions of the operational

Figure 4-2.—The Link-11 communications system.

4 - 2

program. The information about these tracks can betransmitted to other units over the Link-11 net. Thecomputer sends data to the data terminal set using 24-bit data words. The computer also receivesinformation about remote tracks from other units inthe net and displays these tracks through the displaysystem.

Shipboard Gridlock System

Gridlock is the matching of track positions heldby other ships with the tracks held by your own ship.Gridlock is a procedure for determining dataregistration correction by comparing remote tracksreceived from a designated reference unit to localdata. Ideally, tracks received from remote units thatare also displayed by onboard sensors should betransparent, that is, in the exact same position on theCRT. If the gridlock system does not providecorrelation between local and remote tracks, theremote tracks may be painted twice and overlap eachother, as shown in figure 4-3.

Figure 4-3.—Tracks out of gridlock.

Failure to maintain gridlock may be the result ofinaccurate positioning data from a ship’s sensor, fromthe Ship’s Inertial Navigation Systems (SINS), or fromthe ship’s gyro. Failure to maintain gridlock may alsobe the result of an inaccurate operator entry.

The SGS compute r pe r fo rms con t inuousautomatic gridlock calculations. In the event of anSGS computer failure, the flow of Link-11 data to theCDS computer is interrupted. To restore Link-11 data

flow, all SGS installations have switches installed thatallow the technician to bypass the SGS computer untilthe fault is corrected.

Link-11 Security Device

A standard model security device, such as theTSEC/KG-40, commonly referred to as the KG-40, isused with the Link-11 system. When the DTS istransmitting data, the KG-40 receives parallel datafrom the CDS computer, encrypts the data, and sendsit to the DTS. When the participating unit (PU) isreceiving data, encrypted data is received from theDTS, decrypted, and sent to the CDS computer.

Because of the specialized training and securityrequirements of cryptographic equipment, we will notcover the internal operation and controls of thesecurity device.

Data Terminal Set (DTS)

The data terminal set (DTS) is the heart of theLink-11 system. The DTS is the systemmodula to r /demodula to r (MODEM). the CDScomputer sends 24 bits of data to the DTS via theSGS computer and the encryption device. The DTSadds six bits of data for error detection and correction.These six bits are called hamming bits. The 30 bitsof data are phase shift modulated into 15 audio tones.These 15 data tones and a Doppler correction tone arecombined into a composite audio signal, which is sentto either the UHF or HF radio for transmission.

The DTS receives the composite audio signal fromthe radio and separates the 15 data tones and theDoppler correction tone. The 15 data tones aredemodulated into 30 data bits. The six hamming bitsare checked for errors and the 24 data bits are sent tothe CDS computer via the encryption device and theSGS computer.

Link-11 Communications Switchboard

The communications switchboard provides formanual switching of the data terminal set andindividual HF and UHF radios. The communicationsswitchboard provides system flexibility and casualty

4-3

recovery capabilities. A typical switchboard willprovide the following interconnections:

The Link-11 data terminal set to one or moreHF radio sets to provide the standard HF Link-11capability

A Link-11 data terminal set to one or moreUHF radios sets to provide UHF Link-11 capability

The same communications switchboard may alsobe used for connecting a Link-4A data terminal set toone or more UHF radios to provide standard UHFLink-4A (TADIL C) capability. Link-4A is coveredin detail later in this book.

Radios

The Link-11 system can operate with either an HFradio or a UHF radio. Long-range communicationsare achieved by the use of the HF system. UHFcommunications are limited to line of sight. “Line ofsight” means the radio wave will not bend over thehorizon; therefore, the use of an antenna mountedhigh on the mast will increase the range of UHFcommunications.

Antenna Couplers

Antenna couplers are used to connect a specificradio set to a specific antenna. The coupler providesfor the correct impedance matching of the antenna andthe radio set. For many of the multicouplers to workproperly, it is extremely important that the correctfrequency spacing be observed. A general rule is toensure a f r equency spac ing o f 15 pe rcen t .Frequencies that are too close together can causeinterference and distortion, increasing the signal-to-noise ratio and causing bit errors in the data.

Antennas

In oversimplifying the theory of antennaoperation, an antenna is just a piece of wire thatradiates electromagnetic energy from the radio intot h e a t m o s p h e r e a n d c o n v e r t s a t m o s p h e r i celectromagnetic radiation into RF current to beprocessed by the radio. As electromagnetic energyfrom the atmosphere passes through this wire, itinduces a current in the wire. This current is fed to

the radio receiver. If the receiver is tuned to the samefrequency as the received signal, the signal can bep r o c e s s e d . T h e s a m e w i r e w i l l r a d i a t e a nelectromagnetic field if current is flowing through it.

The frequency at which a radio operatesdetermines what size antenna is most suitable fortransmitting and receiving. The higher the frequency,the smaller the antenna will be. Lower frequenciesrequire larger antennas. For example, the full-wavelength of an antenna designed to operate at 4 MHz isabout 250 feet long. Since this length is too large forshipboard application, antennas are designed insubmultiple lengths. These include half-wave andquarter-wave antennas. An antenna can be tuned byintroducing a capacitive or inductive load. Thisloading effectively changes the electrical length of theantenna and can be used to extend the frequency rangeof the antenna. For more information on antennadesign and operation, refer to the Navy Electricity andElectronics Training Series, Module 10, IntroductionTo Wave Propagation, Transmission Lines, andAntennas, NAVEDTRA B72-10-00-93.

Transmission Cycle

The data flow for the Link-11 transmission cycleis shown in figure 4-4. The CDS computer receivesdata from the various ship’s sensors, navigationsystems, and operator entries, and stores this data in adata base. When a Link-11 transmission is required,the computer outputs parallel digital data through theSGS computer to the cryptographic device. Thecryptographic device encrypts the data and sends theencrypted data to the data terminal set (DTS). TheDTS converts the digital data to analog audio tones,keys the transmitter using the radio set keyline, andpasses the audio tones, via the communicationsswitchboard, to the transmitter for modulation to theRF carrier signal. The radio set keyline is a signal thatswitches the radio to transmit mode when the set andreceive mode when clear.

When you are using the HF band, the radiofrequency signal modulat ion uses ampli tudemodulation independent sideband; that is, the uppersideband (USB) and lower sideband (LSB) aretransmitted independently in an effort to overcome

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propagation-caused signal losses. The UHF radio

Figure 4-4.—Link-11 data flow for the transmit cycle.

transmitted independently in an effort to overcomepropagation-caused signal losses. The UHF radiouses frequency modulation; therefore, only the USBis used.

Receive Cycle

When a transmitted signal is received, the receiverdemodulates the audio tones from the RF carrier andpasses them via the communications switchboard tothe DTS. The DTS demodulates and demultiplexesthe audio tones into digital data. The digital data issent to the cryptographic device where it is decryptedand sent to the CDS computer for processing.

LINK-11 NET OPERATING MODES

Before we look into the actual operation of thedata terminal set, you need to have some knowledgeof the Link-11 modes of operation and how themessages are formed. Link-11 employs networked(net) communications techniques for exchangingdigital information among airborne, land-based, andshipboard systems. As you have seen, the amount ofhardware required to support Link-11 operations isr e l a t ive ly sma l l ; however , e s t ab l i sh ing andmaintaining a successful link can be very complex.

Establishing a Link-11 Net

The establishment of a successful link involvesthe interaction and teamwork of the operators andtechnicians of several units working toward thecommon goal. If one unit is having trouble with thelink radio, data terminal set, or other equipment, it canmake the entire link unreliable.

When a task force is about to deploy, the taskforce commander will issue a message that has thenecessary information required to establish Link-11communications. The information in this messageincludes a list of primary and secondary frequencies,designation of the initial net control station, initialgridlock reference unit (GRU) designation, PUidentification and addresses, initial data link referencepoint (DLRP), and other required operat ingprocedures. Voice communications are also requiredfor net control and coordination during initialization.

When the task force is formed, the picket stationsinform the net control station (NCS) of their readinessto establish link operations. Upon establishingcommunication with all units, NCS transmits NetSynchronization (Net Sync). If the NCS is usingcorrected timing (normal mode), the Net Sync verifiesthe communications path between NCS and all picketunits. If a picket unit cannot receive Net Sync, itcannot participate in the net. Net Test should followNet Sync. Net Test is used to confirm connectivitybetween the Link-11 units. Units having difficulty inreceiving Net Sync or Net Test should report to NCSthat they are not able to participate in the net and thenbegin corrective action.

When Net Test is completed, all picket stationsreport their status to NCS. Then NCS directs all PUsto switch to the Roll Call mode and initiate linkoperations. Net Synchronization and Net Test areused in the initialization of the net. The normal modeof operation is Roll Call.

The above scenario has introduced you to severalnew terms and modes of operation. These areexplained in detail in the following paragraphs.

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The following are the six modes of Link-11operation:

Net Synchronization

Net Test

Roll Call

Broadcast

Short Broadcast

Radio Silence

Net Synchronization

The Net Sync mode of operation is used toestablish a uniform time base from which all net datacommunications normally initiate. The Net Syncmode is usually initiated when establishing a link netafter al l operator entr ies have been properlycompleted. The Net Sync transmission is manuallystarted by the operator on the NCS platform andcontinuously transmits the Link-11 preamble untilstopped by the operator.

The preamble consist of two tones–the 605-Hztone and the 2,915-Hz tone. During the transmissionof Net Sync, the 2,915-Hz tone is periodically phasedshifted 180 degrees. The time between these shifts isdetermined by the selected data rate and is called aframe.

Each PU is equipped with a very accurate timebase in the form of a frequency standard (internal orexternal). When the NCS transmits Net Sync, eachunit receiving the transmission synchronizes itsindividual time base with the Net Sync signal. If thepicket station is operating in the corrected sync mode,as is normally the case, the picket will check to seethat it can recognize the Net Sync signal as a means ofverifying that a good radio link has been established.If a picket is going to operate in the stored sync mode,it will align its stored frame timing to the timing ofthe NCS, using the received Net Sync signal. Sincestored sync timing locks the picket to the time base ofthe NCS, data from other pickets may be lost.

Therefore, this mode should only be used during timesof poor radio propagation or signal jamming. Afterthe completion of Net Sync, the next operationperformed in establishing a link is usually Net Test.

Net Test

Net Test provides an overall evaluation of the netand equipment performance. When you are operatingin this mode, NCS will broadcast canned test data toall pickets within the net. The data terminal setcontains a code generator that generates twenty-one30-bit data words. Once all the words in the wordtable have been generated, the process automaticallystarts over and keeps running until stopped by theoperator.

Net Test will test the connectivity between allunits and the operation of the DTS. Since it is a localtest, Net Test does not check the interface between theCDS computer and the DTS. Net Testis also helpfulto the technician for setting the audio input and outputlevels of the DTS or radio set.

Roll Call

Roll call is the normal mode of operation. In thismode, the operator on the NCS platform entersownship’s address and an assigned address (PUnumber) for each PU in the proper switch position.When the link is initiated, each PU is polled for data.Polling consists of sending a call-up message. If thePU fails to respond, the call-up is repeated. If the PUstill does not respond, it is skipped and the next PU ispolled. When a PU recognizes its own address, thePU will transmit its data to all the participants in thelink. When the NCS recognizes the end of the PUreply, it automatically switches to the transmit modeand calls up the next PU address. After all the unitsin the net have been polled, the NCS transmits its owndata and the process is continuously repeated. Theroll call mode provides all PUs with continuous, nearreal-time exchange of tactical information.

Broadcast

When the broadcast mode is used, one PU willcontinuously send a series of data transmissions to all

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the members of the net. Once manually initiated, thetransmission will continue to be sent automaticallyuntil the operator manually stops it. Through the useof the broadcast mode, other picket stations canreceive real-time tactical information withoutbreaking radio silence.

Short Broadcast

In the Short Broadcast mode, a picket station orthe NCS sends a data transmission to the othermembers of the net. The transmission is initiated bythe operator depressing the TRANSMIT STARTbutton on the DTS control panel and is terminatedautomatically when the computer has finished sendingthe DTS data. This mode is used only when no otherunit is transmitting.

Radio Silence

In the Radio Silence mode, the radio set key lineand the data terminal set audio output are disabled.The receive capability of the DTS is not affected. TheRadio Silence mode is manually initiated andterminated.

BUILDING A LINK-11 MESSAGE

Information transmitted from the DTS originatesfrom two sources. Tactical data always originatesfrom the CDS computer. Other information,including the preamble, phase reference, start andstop codes, and address frames, originates within thedata terminal set. These additional special-purposeframes are added to the data frames to form the propermessages.

For the DTS to control the net properly, strictadherence to the correct message format and netprotocol are required. Every Link-11 message has aspecific format and function. Each Link-11 messagegenerated by the DTS begins with a header consistingof the preamble (five frames) and the p h a s ereference frame (one frame). Control codes, such asthe start code, the picket stop code, and the controlstop code, are also required.

Preamble

The preamble, as previously covered, consists ofa two-tone signal. The two tones are the 605-HzDoppler tone and the 2,915-Hz sync tone. Thepreamble is five frames long and is transmitted at fourtimes the normal power, as shown in figure 4-5.Normal power for the 605-Hz Doppler tone is +6 dBand the data tones, including the 2,915-Hz tone, is 0dB. During the preamble, the 605-Hz tone istransmitted at +12 dB, and the 2,915-Hz sync tone istransmitted at +6 dB. The sync tone is shifted 180degrees for each frame to allow the receiving DTS todetect frame transitions.

Figure 4-5.—The Link-11 preamble power levels andframe count.

Phase Reference Frame

The phase reference frame follows the preambleand is shown in figure 4-6. This frame is composedof the normal 16-tone composite signal with the datatones transmitted at 0 dB and the Doppler tonetransmitted at +6 dB. Since the two bits of data storedin a tone is based on a certain phase shift in respect tothe preceding frame, the phase reference frameprovides the reference for the first frame of data.Each succeeding frame becomes the phase referencefor the following frame.

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Figure 4-6.—The phase reference frame added to thepreamble with normal data tone levels.

Information Segment

The information segment of the Link-11 messageis composed of control code frames and message dataframes. Control code frames consist of a start code,a stop code, and an address code. Each control codeis two frames in length and performs a specificfunction. Control codes are not sent to the CDScomputer.

Figure 4-7.—The start code added to the Link-11transmission.

START CODE. —The start code is a two-framecode that follows the phase reference frame, as shownin figure 4-7. When sensed by the DTS, the start code

causes the DTS to send the Prepare-to-Receive Datainterrupt to the CDS computer.

MESSAGE DATA FRAMES. —Message dataframes contain the tactical data being disseminatedand follow the start code, as shown in figure 4-8. Thenumber of message data frames depends on theamount of tactical information the unit transmits. The24 bits of data contained in each frame is sent to theCDS computer.

Figure 4-8.—The message data frames added to theLink-n transmission.

STOP CODE. —The stop code is a two-framecode that follows the data message in a Link-11transmission and is shown in figure 4-9. There aretwo types of stop codes: the control stop code and thepicket stop code. The control stop code is used inmessages originated by NCS (NCS report) andindicates that a picket address code follows the stopcode. The picket stop code indicates to the NCS thatthe p icke t un i t has comple ted i t s messagetransmission. Both the control stop code and picketstop code cause the receiving DTS to send the End-of-Receive interrupt to the CDS computer.

LINK-11 MESSAGE FORMATS

The formats of the messages transmitted by theLink-11 system vary with the mode of operation.

Roll Call Mode Messages

In the roll call mode, the unit designated as the netcontrol station sends out two types of messages.These are the NCS call-up message (interrogation)and the NCS report (message with interrogation). Athird message, the picket reply message, is sent bypicket unit in response to interrogation messages.

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Figure 4-9.—The stop codes added to the Link-11transmission.

C A L L - U P ( I N T E R R O G A T I O N )MESSAGE. —This message shown in figure 4-10consists of the five-frame preamble, the phasereference frame, and the two address frames. Thecall-up message does not use start and stop codes.

Figure 4-10.—The NCS call-up message.

N C S R E P O R T A N D C A L L - U PMESSAGE. —This message shown in figure 4-11consists of the five-frame preamble, the phasereference frame, the two-frame start code, the dataframes containing the NCS report, the two-framecontrol stop code, and two frames containing theaddress code for the next PU.

Figure 4-11.—The NCS report and call up message.

PICKET REPLY MESSAGE. —The picketreply message shown in figure 4-12 consists of thefive-frame preamble, the phase reference frame, the

two-frame start code, the data frames, and the two-frame picket stop code.

Figure 4-12.—The picket reply message.

Short Broadcast Messages

The Short Broadcast is a single data transmissionto all members of a net by a station that maybe actingas either picket or NCS. It is the same format as thepicket reply message shown in figure 4-12. The ShortBroadcast message is manually initiated by theoperator at the DTS.

Broadcast Mode Messages

The Broadcast mode messages consist of acontinuous series of short broadcast messages,separated by two frames of dead time, as shown infigure 4-13. The message format is the same as apicket reply message. In the Broadcast mode, onlyone unit will transmit.Net Test Mode

The Net Test message consists of the five-framepreamble, the phase reference frame, and the Net Testwords generated by the DTS. When all the Net Testwords in the library have been transmitted, thesequence starts over until the operator stops the NetTest.

LINK-11 DATA TERMINAL SET (DTS)

As you have seen, the data terminal set is the heartof the Link-11 system. The DTS performs themodulation, demodulation, and control functionsrequired for proper Link-11 operation. It accepts datafrom the CDS computer in the form of 24-bit datawords, adds six bits of error detection and correction(EDAC) data, and converts all 30 bits into an audiotone package that is sent to the transmitter portion ofthe radio set. The key-line signals necessary to

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Figure 4-13.—Broadcast mode message format.

control the transmit and receive states of the radio setare also generated by the DTS. Data received fromthe upper sideband (USB) and lower sideband (LSB)portions of the radio set receiver, in the form of audiotones, is converted into parallel binary data and sent tothe CDS computer.

Currently several design generations of Link-11data terminal sets are used in the fleet. These includethe AN/USQ-59 and 59A, the AN/USQ-63, and theAN/USQ-74. Originally introduced in the early1960s, each successive generation of the Link-11 dataterminal set reflects additional knowledge gainedfrom fleet use and advances in technology. Althoughthe technology used in the different models of theLink-11 DTS may be vastly different, all of themperform the same function. Normally, the DTSoperates in the half-duplex mode, meaning it can

either receive or transmit data, but it cannot do both atthe same time. An exception is during system testwhen the DTS operates in full-duplex mode and cansimultaneously send and receive data.

DATA TERMINAL SET FUNCTIONS

The DTS also performs the following functions:

Error detection and correction

Audio signal generation

Link-11 protocol and interface control

Error Detection and Correction (EDAC)

The DTS receives data from the CDS computer inthe form of 24-bit binary data words. The 24-data bits

Table 4-1.—DTS Parity Bit Status Codes

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are expanded to 30 bits by adding six bits for errordetection and correction (EDAC). These six bits arealso called hamming bits. The value of these bits arebased on parity checks of specific combinations of the24-bit data word.

During the receive cycle, the six EDAC, orhamming bits, are examined for errors. There isenough redundancy in the EDAC to allow forcorrection of a single bit error. The operator cancontrol the selection of the error correction mode. Ifthe data word is not a control word, the word isexamined to determine if it is error-free, contains acorrectable error, or contains uncorrectable errors. Ifthe DTS is in the error detection and label mode, adetected error is identified and labeled before the dataword is sent to the CDS computer. In the errordetection and correct mode, the DTS attempts tocorrect an error before sending the data word to theCDS computer. In both modes, the six EDAC bits aredeleted and replaced with two parity error status bits.These status bits are defined in table 4-1.

Audio Tone Generation and Characteristics

The DTS converts the 24-bit data word, alongwith the six EDAC bits, into a composite audio signalconsisting of 16 tones. This composite 16-tone signalis the data frame. The tones range in frequency from605 Hz to 2,915 Hz and are the odd harmonics of 55Hz. The specific frequencies of the tones are shownin table 4-2. The 605-Hz tone is used for Dopplercorrection, and the 2,915-Hz tone is used for data andsynchronization. Each of the data subcarrier tones(tones 2 through 16 in table 4-2) represents two binarybits of differential quadrature phase-shift modulateddata.

The Dopple r tone (605 Hz) i s no t phasemodulated. It is used to correct for Doppler shifts inthe received tones caused by the relative motion

between the transmitter and the receiver. It is alsoused to correct for the Doppler shift that may occurbecause of differences between the transmitter andreceiver frequency standards.

The 2,915-Hz tone has two separate uses. Duringthe transmission of the preamble and Net Sync, the2,915-Hz tone is used to identify frame timing. Thistone is phase shifted 180 degrees at the end of eachframe. When detected by the receiving DTS, thephase shift indicates the start of a new frame. Whenthe DTS is in corrected timing, this information isused to set the timing for the data frames that follow.When stored timing is used, the frame timing that wasset during Net Sync is used.

The Doppler and sync tones vary from each otherand the other data-carrying tones in amplitude. TheDoppler tone is 6 dB greater than the other tones.During the Net Sync and preamble frames, theDoppler tone is transmitted at 12 dB and the sync toneis transmitted at 6 dB. The Doppler tone istransmitted at 6 dB during the transmission of dataframes and the sync tone is used as a data tone. Datatones are transmitted at 0 dB.

The audio tones are divided into data frames toidentify the separate parallel groupings of 30 bits. Itis the phase angle shift of each of the 15 data tonesthat conveys the digital information contained in thetone. During each frame, each data tone frequencyhas a particular phase. At each frame boundary, thephase of each data tone is shifted with respect to theprevious frame. The amount of this phase change, orphase difference, determines the value of a two-bitnumber Two data bits yield the following fourpossible combinations: 00, 01, 10, and 11. Eachcombination is associated with a phase difference ofone of four values: 45 degrees, 135 degrees, 225degrees, or 315 degrees from the previous position.

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Table 4-2.—Tone Library

* There is no bit location associated with the 605-Hz Doppler tone or the 2,915 Hz tone when used as the Sync tone

Figure 4-14.—Link-11 data phase shift encoding.

Each of these angles marks the center of aquadrant, as shown in figure 4-14. Each 90-degreequadrant is assigned a two-bit binary value. Anyphase difference fal l ing within that quadrantrepresents that binary value. This system of dataencoding can tolerate an error in the prescribed phaseshift of up to ±44 degrees before a single bit error willoccur. An error in phase shift that is greater than 45degrees, but less than 135 degrees, will cause thephase angle to fall into an adjacent quadrant. Noticethat the values are assigned to each quadrant in sucha way that if a phase shift error occurs, that only onebit error will be introduced as long as the quadrantinto which it falls is adjacent to the target quadrant.

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Link Protocol and Interface Control

In addition to encoding data from the CDScomputer, the DTS generates and recognizes protocoldata that controls the type and number of linktransmissions. These protocol words include codesindicating the start of transmission, the end oftransmission, and the address of the next unit totransmit.

The interface with the CDS computer is under thecontrol of the DTS. The DTS signals the CDScomputer when it has input data or when it wantsoutput data through the use of external interrupts.These interrupts include the prepare-to-transmit,prepare-to-receive, and end-of-receive interrupts.

DTS CONTROLS AND INDICATORS

Many parameters that affect the operation of theDTS are under the operator’s control, whether thestation is operating as a picket or as the net controlstation. Both the operator and the technician must befamiliar with the various controls and indicatorsassociated with the DTS. The AN/USQ-59 usesseveral control panels that are usually mounted next tothe operator’s display console. These panels enablethe operator and the technician to control and monitorthe net operation.

The control panels include a Mode Control panel,a TADIL A Control panel, and an Address SelectionIndicator panel. Although the AN/USQ-59 controlpanels are used here to show the controls andindicators of a Link-11 DTS, other data terminal setshave similar controls. The functions controlled by theAN/USQ-59 control panels are software controlledon newer data terminal sets. On these data terminalsets, the entries an made via the computer controlconsole or the display console.

DTS Mode Control Panel

The DTS mode control panel controls andindicators are shown in figure 4-15. The following isa summary of how the controls affect the operation ofthe link and what the indicators mean.

TRANSMIT MODE INDICATOR —lightswhen the DTS is in the transmit mode.

RECEIVE MODE INDICATOR —lights whenthe DTS is in the receive mode.

SUMMARY FAULT INDICATOR —Lightswhen a fault in the DTS is detected while in theOPERATE mode. There are 27 performance monitorfault-sensing circuits in the data converter (modem) ofthe DTS. During the OPERATE mode, 14 of thesesensors can cause a summary fault. The fault-sensingcircuits monitor areas such as various power supplies,signal quality, preamble presence, timing, and audiosignal quality. When the DTS is in SELF TEST, thesummary fault lamp is lighted when a fault is isolatedto a function defined by switch positions on the faultisolation control and built-in tests routines.

LAMP TEST BUTTON —causes all indicatorson the mode control panel, the TADIL A controlpanel, and the address control unit to light.

FAULT MONITOR/RESET SWITCH —In theMONITOR position, this switch allows the fault-sensing function of the DTS to operate normally andprovide a fault summary signal to the DTS control. Inplaced in the RESET position, the fault-sensingcircuits of the DTS are reset. The SUMMARYFAULT lamp is turned off when the fault-sensingcircuits are reset.

I N T E R N A L 1 0 0 - K H Z / E X T E R N A LSWITCH —Allows for the selection of the internal orexternal 100-KHz frequency standard.

D O P P L E R C O R R O N / C O R R O F FSWITCH —Enables the DTS Doppler correctionwhen placed in the CORR ON position.

FULL-DUPLEX/HALF-DUPLEXSWITCH —In the FULL-DUPLEX position, this switch enablesfull-duplex operation of the data converter and thecomputer I/O adapter. It also enables loop backprocessing of the transmit sidetone data for input tothe computer. In the HALF-DUPLEX position, theDTS operates in the half-duplex mode and thetransmit sidetone is disabled from being processed

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Figure 4-15.—The AN/USQ-59 mode control panel.

and input to the computer. Link-11 uses the half-duplex mode.

SIDEBAND SELECT SWITCH —When theSIDEBAND SELECT switch is placed in the LSB orUSB position, the DTS processes only the lowersideband or upper sideband of the received signal.When the switch is in the DIV position, the DTScombines both the upper sideband and the lowersideband signals to create frequency diversity data forinput to the computer. When the switch is in theAUTO position, the DTS selects the signal with thebest receive quality for processing. The AUTOposition is the normal position of this switch.

DATA RATE SWITCH —Selects the data ratethat the data converter uses. When the switch is in theDUAL 1200 position, the data converter can transmitand receive two unrelated streams of data at 1200 bps.In the 1200 and 2400 positions, the data converter

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transmits and receives a single data stream at 1200and 2400 bps, respectively. When the switch is in theTADIL A position, the data rate is controlled by theDATA RATE switch on the TADIL A control panel.The TADIL A position is the normal position forLink-11.

SYNC MODE SWITCH —The SYNC MODEswitch selects the mode of synchronization used bythe DTS receive circuitry and is used in conjunctionwith the TIMING STORED/CORRECTED switch onthe TADIL A control panel. The normal operatingposition for the SYNC MODE switch is in theFAST/CONT position.

When the switch is in the FAST/CONT position,both the fast and continuous synchronization circuitsof the DTS are selected. Synchronization is initiallyobtained during the f ive-frame preamble andmaintained continuously during the data portion of thetransmission. The TIMING switch on the TADIL Acontrol panel must be in the CORRECTED position.

W h e n t h e F A S T p o s i t i o n i s s e l e c t e d ,synchronization is only during the five-framepreamble. If the CONT position of this switch isselected, only the continuous synchronization circuitsare selected. Synchronization is obtained only duringthe data portion of the transmission. The TIMINGswitch on the TADIL A control panel must be in theCORRECTED position for both of these modes.

The INHIBIT position of this switch disables boththe fast and continuous synchronization circuits of theDTS. The DTS will maintain the time base that wasstored when the switch was turned to INHIBIT. Forsynchronization to be held, the unit with its syncmode inhibited must maintain its original geographicrelationship to all other units in the net. This positionis used when the received signal contains interferencethat could cause loss of synchronization.

OPERATE/SELF-TEST SWITCH — T h i sswitch must be in OPERATE for normal on-lineoperations. When the switch is placed in the SELF-TEST mode, the DTS is placed in an off-line modeand the fault isolation circuitry is enabled.

Figure 4-16.—The AN/USQ-59 TADIL A control panel.

CONTROL ON/OFF SWITCH —When theCONTROL switch is placed to the ON position,+28Vdc is applied to the fault isolation control panel,the mode control panel, the TADIL A control panel,and the address control panel.

TADIL A Control Panel

The TADIL A control panel provides the controlswitches and indicators required to control andmonitor Link-11 operations. Figure 4-16 shows theAN/USQ-59 TADIL A control panel.

XMT DATA ERROR INDICATOR. —Thisindicator is lighted when the DTS detects an errorwhile transmitting data in the TADIL A, or Link-11,mode.

RCV DATA ERROR INDICATOR. —Thisindicator is lighted when the DTS detects an error inreceived data being sent to the CDS computer.

CODE ERROR INDICATOR. —The CODEERROR indicator is lighted when the DTS detects anerror in the received or sidetone (transmit) controlcodes during TADIL A operations.

NET BUSY INDICATOR. —The NET BUSYindicator is lighted when the DTS detects that thecommunications net is busy. It is activated when asignal called signal presence is generated by theDTS .

SYNC COMPT INDICATOR. —The SYNCCOMPT indicator is lighted continuously, or flashes,when the DTS has achieved synchronization with theNCS data terminal.

T I M I N G S T O R E D / C O R R E C T E DSWITCH. —The TIMING STORED/CORRECTEDswitch determines how the DTS is synchronized.When the switch is in the CORRECTED position, thefas t synchron iza t ion and /o r the con t inuoussynchronization circuitry in the DTS is used. Theposition of the sync mode switch on the mode controlpanel determines whether the fast, continuous, or bothcircuits are used to maintain synchronization. In theSTORED position, the DTS uses the time base storedduring Net Sync. During normal operations, thisswitch should be in the CORRECTED position.

OPERATE/RADIO SILENCE SWITCH. —TheOPERATE/RADIO SILENCE switch is a two-position toggle switch that allows the DTS to inhibitradio transmissions. In the OPERATE position, theDTS operates normally. When switched to theRADIO SILENCE position, the radio keyline andtransmit audio circuits are immediately disabled.

NET CONTROL/PICKET SWITCH. —TheNET CONTROL/PICKET switch configures the DTSto operate as the net control station or a picket stationin roll call mode.

ERROR CORRECT/LABEL SWITCH. —TheERROR CORRECT/LABEL switch determines howthe DTS processes de tec ted e r ro r s . In theCORRECTED position, the DTS attempts to correctdetected errors. If a single bit error is detected, thelocation of the erroneous bit is detected and corrected.

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If an even number of bit errors occurs, the correctioncircuitry is inhibited. If an odd number of bit errorsoccurs, the correction circuitry attempts to correct thedata; however, if an odd number of multiple bit errorsoccurs, an erroneous correction is made. When theswitch is in the LABEL position, the DTS does notattempt to correct detected errors. Instead, the dataword sent to the computer is labeled to indicate thaterrors were detected in the data word.

T R A N S M I T R E S E T S W I T C H . — T h eTRANSMIT RESET switch is a momentary contactpushbutton switch. When depressed, this switchcauses any transmission in progress to be terminated.The DTS stops the transmission by inhibiting thegeneration of the output data request, causing a stopcode to be transmitted. The DTS also resets theaddress control address sequence logic.

TRANSMIT INITIATE SWITCH. — T h eTRANSMIT INITIATE switch is a momentarycontact pushbutton switch that causes the DTS toinitiate data transmission when the DATA RATEswitch is in the TADIL A position. The TRANSMITINITIATE switch must be depressed to initiate allDTS transmissions except when the DTS isconfigured as a picket and is in the roll call mode.When the net is in the roll call mode, only the netcontrol station is required to initiate transmission bydepressing the TRANSMIT INITIATE switch.

MISS CALL INDICATOR. —The MISS CALLindicator is lighted when the net control station hasdetected no response from a picket station after twosuccessive interrogations. Once lit, it will remain lituntil a picket responds or the TRANSMIT RESETswitch is depressed.

A D D R E S S C O M P U T E R / C O N T R O LS W I T C H . — T h e A D D R E S SCOMPUTER/CONTROL switch determines thesource of the address used by the DTS. When theswitch is in the CONTROL position, addresses areobtained from the address control unit. In theCOMPUTER position, addresses are obtained fromthe CDS computer, provided the computer isconfigured for external function operations. Thenormal position for this switch is dependent on the

configuration of the system on your ship.

NET MODE SWITCH. —The NET MODEswitch determines the mode of operation of the DTS.The modes are BC or broadcast, SHORT BC, ROLLCALL, NET SYNC, and NET TEST.

DATA RATE SWITCH. —The DATA RATEswitch determines the speed and frame timingoperation of the DTS. When the switch is in the1364/9.09 position, the DTS transmits and receivesdata at 1364 bps. The data frame phase identificationinterval is approximately 9.09 milliseconds. Whenthe switch is in the 2250 position, the DTS transmitsand receives data at a rate of 2250 bps and a frameinterval of 9.09 milliseconds. When the switch is inthe 1364/1 8.18 position, the data rate is 1364 bps, butthe frame phase shift interval is increased to 18.18milliseconds.

OWN STATION ADDRESS SWITCH. —TheOWN STATION ADDRESS switch consists of twothumb wheel switches in which an address is enteredto identify the address the DTS will respond to as itsown. In the roll call mode and with the DTSconfigured as a picket station, the DTS will transmitits tactical data when the interrogation messageaddress matches the address entered into the OWNSTATION ADDRESS switches.

RANGE IN MILES SWITCH. —The RANGEIN MILES switch also consists of two thumb wheelswitches. These switches are used to select theapproximate distance between the net control stationand the picket station. The range entered into theseswitches causes the DTS to alter the frame timing tocompensate for the signal propagation delay betweenthe picket station and NCS. The range in milessetting for the NCS is always zero miles.

Address Control Indicator

The address control indicator is used to set theaddress of the picket stations to be interrogated whena unit is configured to operate as the NCS. Theaddress control indicator is shown in figure 4-17. Theaddress control indicator consists of 20 identicaladdress selection modules, which are used to address

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up to 20 stations. More than one address controlindicator may be installed in a system to provide theability to interrogate more than 20 stations.

Each address selector module has two thumbwheel switches in which one of 64 octal addressesmay be entered (address 00 and 77 octal are invalid).Also, each address selector module has a power on/offswitch, a power on indicator lamp, and a callindicator, as shown in figure 4-18.

When a unit is configured as the NCS, theoperator enters all the assigned addresses of the netparticipating units into the address selector modules,and turns on each module with a valid address. Oncethe roll call mode is initiated, the DTS will check eachmodule sequentially. If the power of the module is onand a valid address is entered, the address is sent tothe DTS for use in an interrogation message. If thepower switch is in the OFF position, that module isskipped, even if it contains a valid address. Whenenabled by the DTS, the address selector modulesends the address entered in the thumb wheels to theDTS and the call indicator light. The call indicatorwill remain lit until the DTS sequences to the nextaddress module.

CDS INPUT/OUTPUT CONTROL

The data terminal set controls the exchange ofdata with the CDS computer. As described earlier,i n p u t / o u t p u t c o m m u n i c a t i o n s p r o t o c o l i saccomplished through the use of external interrupts.The prepare-to-transmit data interrupt, the prepare-to-receive data interrupt, and the end-of-receive datainterrupt are used to control most of the DTS to thecomputer interface.

CDS Computer Input (Receive) Data Cycle

The input data cycle is initiated by the DTS.When the DTS recognizes the second frame of thestart code, it sets the prepare to receive data interrupton the input data lines and sets the external interruptline. The computer acknowledges the receipt of theinterrupt by sending an input data acknowledge (IDA)to the DTS.

Figure 4-17.—The Address Control Indicator C9062/U.

Upon receipt of the first message frame, the DTSdemodulates the 24-bit word and places it on the inputdata lines, along with the two error detection andcorrection bits. Once the data is placed on the inputdata lines, the DTS sets the input data request (IDR)line. The computer will sample the data and send anIDA. This process repeats for all frames of themessage. The first frame of the stop code is alsotreated as a message frame and sent to the CDScomputer. When the DTS recognizes the secondframe of the stop code, it will place the end of receive

Figure 4-18.—An address selector module.

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interrupt on the input data lines and set the interruptline. The interrupt is then processed by the CDScomputer and the input buffer is closed.

If the received stop code is a picket stop code, theDTS simply resets itself. If the stop code is a controlstation stop code, the DTS will compare the next twoframes received with its own station address code.

CDS Computer Output (Transmit) Data Cycle

The output data cycle is initiated when the DTSdetects i ts own stat ion address, ei ther in aninterrogation message or at the end of an NCS reportand interrogation message. When the DTS recognizesits own station address, it starts to transmit thepreamble. During the first frame of the preamble, theDTS sets the prepare to transmit interrupt on the inputdata lines. The computer samples the interrupt andsends an IDA to acknowledge receipt of the interrupt.

The DTS finishes sending the preamble and phasereference frames During the second frame of thestart code, the DTS sets the output data request (ODR)active, requesting the first word of the tactical data.The CDS computer responds by placing 24 bits ofdata on the lines and then setting the output dataacknowledge (ODA). The DTS samples the data andclears the ODR. The first frame of data is processedfor transmission and the ODR line is then set torequest the next data word.

This procedure is repeated until all the data wordshave been transmitted. Once the CDS computer hascompleted sending all the data words, it will notacknowledge the ODR from the DTS. If the CDScomputer has not acknowledged an ODR from theDTS in a preset amount of time, the DTS will clearthe ODR line and generate a stop code. Upontransmission of the two-frame stop code, the DTS willreturn to the receive mode.

Net Control Station (NCS) I/O Operations

The station acting as NCS follows the sameprotocols when communicating with the CDScomputer. Some differences exist in the generation ofthe control codes. The net control s tat ion isresponsible for interrogating each station. Upon

receipt of a picket stop code, the DTS checks the nextstation address and sends an interrogation message.After the interrogation message is transmitted, theDTS waits to receive a start code from theinterrogated station. If a start code is not recognizedafter 15 frame intervals , the stat ion wil l bereinterrogated. If a start code is not received afteranother 15 frame intervals, the address control unitwill advance to the next active picket address and theinterrogation process is repeated.

The other major difference is when the net controlstat ion has completed i ts own tact ical datatransmission, a control stop code, followed by thenext station address, is transmitted. Again, if a startcode is not received within 15 frame intervals, asecond interrogation is sent. This secondinterrogation is a normal interrogation messageconsisting of the preamble, phase reference frame, andaddress code.

Modulator/Demodulator

The modulator/demodulator function of the DTSprovides the digital to analog and analog to digitalconversion. During data transmission, the 24-bitbinary data word is expanded to 30 bits by adding thesix bits for error detection and correction. The 30 bitsare then examined in pairs to determine the requiredphase angle shift for each of the 15 data-carryingtones in the audio package.

At the frame boundary, the phase of each data toneis shifted with respect to the previous frame. Figure4-19 shows the four possible phase shifts. A sixteenthtone, the 605-Hz Doppler correction tone, is added tothe tone package. The Doppler tone is not phasemodulated and is used to correct for Doppler shiftscaused by the r e l a t ive mot ion be tween thetransmitting station and the receiving station. The 16tones are combined into a composite audio signal andsent to the radio set. The radio set transmits thecomposite tone package on the carrier frequency inindependent sideband form.

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Figure 4-19.—Link-11 frame boundary phase shifts.

During receive operations, the tone package isreceived from the radio set. The 30 bits of data areextracted from the tone package by determining thephase shift of each data tone with respect to theprevious frame. The 30 bits, which contain 24-databits and six-EDAC bits, are examined for errors. Thesix-EDAC bits allow for the detection of errors andprovide enough redundancy to allow for correcting asingle bit error.

The operator can select whether or not the DTSattempts to correct detected errors, as explainedearlier in this chapter. In the error detect (label)mode, a detected error is identified and labeled beforeit is sent to the CDS computer. In the error correction(correct) mode, the DTS attempts to correct a detected

error, labels the error, and sends the data word to theCDS computer.

The DTS is capable of receiving and processingboth the upper sideband and the lower sideband whenusing a HF radio, depending on the position of thesideband select switch. When you are using a UHFradio, only the upper sideband is received andprocessed.

If the sideband select switch is in the USB or theLBS position, only the designated sideband isprocessed. In the diversity (DIV) mode, the 30-bitword is generated by adding the relative phase anglesof the USB and the LSB.

Because of propagation anomalies, noise, andinterference, the AUTO mode can be used to selectthe sideband (USB, LSB or DIV) that yields the mostcorrect data automatically. In the AUTO mode theDTS processes a word from each sideband and thediversity combination. The decoded words areexamined for errors in the following order or priority:DIV, USB, and LSB. A search of the three words ismade to find a data word with no error. If one isfound, it is selected for input to the CDS computer. Ifnone is found, the RCV DATA ERR indicator is litand the diversity combination data word is sent to theCDS computer.

Radio Set Interface

The DTS generates the following outputs to theradio set: upper sideband composite audio, lowersideband composite audio, and key line. It receivesupper sideband composite audio and/or lowersideband composite audio. UHF radio sets use onlythe upper sideband signal and the key-line signal.

The key-line signal controls the transmit andreceive state of the radio set. The key line is set totransmit Link-11 data. When the key-line is cleared,the radio set returns to the receive mode.

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CHAPTER 5

LINK-11 FAULT ISOLATION

INTRODUCTION

A communications network, such as the Link-11 system, can be very complexwhen the goal is to maintain high-quality communications with all units in the net.Distance, atmospheric anomalies, corrosion, and even the time of day can affect thequality of Link-11 communications. The Link-11 technician has many tools toenable him to pinpoint problems. However, oftentimes the technician maymisunderstand such tools, forget them, or not have the knowledge to use themeffectively.

Problems occurring with Link-11 communications are best approached by meansof the team concept. A typical link team is usually composed of a team leader, anET, a FC, an OS, and an RM. The team leader is usually a senior ET and could bethe electronics material officer (EMO) or combat systems maintenance officer.

After completing this chapter, you should be able to:

Describe the procedures required for running single stationProgrammed Operational and Functional Appraisal (POFA) on theDTS.

State the circuits verified by the successful completion of single stationPOFA.

Describe the procedures for running multi-station Link-n POFA.

Describe the components of the LMS-11.

Describe the information presented in each of the LMS-11 displaymodes.

Recognize common Link-n problems as displayed on the LMS-11.

LINK-11 MYTHS AND FACTS

When a Link-11 problem occurs, usually the link troubleshooting team is calledto the combat direction center. Here they can meet with the operator, talk to otherships in the link, and analyze the displays on the LMS-11. Through these initialsteps, the team can determine several things, such as whether the problem is local orif the entire net is experiencing problems. Because of the complexity of linkequipment, a variety of methods were used over the years to solve link problems. Ifa particular action worked once, it was often assumed that it would work in allinstances. Over the years, this led to a type of folklore or mythology on howtechnicians were to troubleshoot the link. Senior link techs would pass these myths

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on to junior link techs and the mythology developed a life of its own. In thefollowing paragraphs, we examine some of these myths and seek to clarify the realproblems that led to the evolution of them.

Myth: Changing the NCS Will Always Solve Net Problems!

Changing the NCS may solve net problems, but only if the current NCS iscausing the problem. What is the problem? If data is not being received from a unitbecause the current NCS has entered the PU number incorrectly, shifting NCSfunctions to a station with the PU data entered correctly will solve the problem.However, it would be easier if the current NCS were simply to enter the correct PUnumbers.

When the current NCS is using a radio set with poor receiver sensitivity and ispolling on top of picket responses effectively jamming the entire net, changing theNCS is imperative. Also, if several units are not recognizing their interrogationsbecause NCS is out of range or in an RF propagation shadow, changing to a unit ina better location should improve net communications.

Myth: Changing Frequency Always Solves Net Problems!

Here again is a myth that has some basis of fact. Changing frequency is a time-consuming process. When all the procedures are not carefully followed, thenchanging the frequency induces additional problems into the net. This mythdeveloped because improperly set switch positions and patch panel configurationswere often set to the proper position during the frequency changing process. Whenthe problem is connectivity on the current frequency, the proper action is to find abetter frequency.

Myth: More Power Improves Link Performance!

This is a myth. On the transmit side, the idea behind the myth is that keeping thelink HF transmitter tuned to maximum output power will result in maximum areacoverage. In fact, constantly outputting maximum power can lead to seriousRFI/EMI problems (on the ship doing so) and will not significantly increase thesignal propagation range.

The idea behind the myth on the receive side is that by keeping the HF receiveraudio output control maximized, receive quality improves. In fact, maximizing theaudio output saturates most data terminal sets. Saturation generally occurs in theDTS at around 3 dBm. Signal inputs above this level actually increase receive dataerrors.

Myth: Dummy PUs Improve Link Quality!

A dummy PU is an address insert into the polling sequence by the NCS for whichthere is no live unit. Dummy PUs cause the net cycle time to increase and netefficiency to decrease. The idea that the NCS must use dummy PUs for the link to

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operate properly is not generally true. It may be true only in infrequent, isolatedcases. Studies have shown that in the old NTDS system (CP-642 computer and theAN/USQ-36 DTS), a dummy PU entered between a live PU and own address wasrequired for NCS data to be output at each NCS report opportunity. Since theCP-642 computer and the AN/USQ-36 DTS have virtually disappeared, dummy PUsshould not be used.

Myth: Radio Silence Reduces Net Cycle Time!

The effect Radio Silence has on net cycle time depends on a number of factors.As you saw in the last chapter, if a PU does not respond to a call up in 15 frames, thePU is interrogated again. After another 15 frames, if the PU still does not respond,then NCS polls the next PU. If the PU that goes to Radio Silence was sendingreports that exceeded 38 frames, then net cycle time would be reduced by the PUgoing to Radio Silence. Effective net management would be to eliminate the PUnumber of the unit that has to go into Radio Silence until that unit is able to reenterthe net.

As you can see, there are several misconceptions on the proper way to manageand troubleshoot the Link-11 system. In this chapter, we concentrate on the toolsavailable to the technician to aid in the isolation of link problems.

LINK-11 PROGRAMMED OPERATIONALAND FUNCTIONAL APPRAISAL (POFA)

Two types of POFAs are used in the Link-11system. These are the single station POFA, used tocheck components of the Link-11 on board a singlestation, and the multi-station POFA, used to check theconnectivity of several units.

SINGLE STATION POFA

The single station POFA is an end-around test thattransfers canned data from the computer through thecrypto device and the data terminal. The singlestation POFA can also be run through the radio set tocheck out part of the audio communications pathfurther.

POFA Setup

The POFA is a special program that is loaded intothe computer. It is very important that you follow theinstruction manual when attempting to run the POFA.The POFA is designed to run in full-duplex mode.Normal link operations use the half-duplex mode.“Full duplex” means the system is configured to

transmit and receive data at the same time. In theDTS, this is accomplished by the transmit audio beingfed directly into the receive input. Also, if the DTS isoperating in full-duplex mode, the rest of the system,especially the crypto device, must be in full duplex.On the KG-40, full duplex is accomplished when thefront panel switch is turned to the POFA TESTposition.

Analyzing Single Station POFA

When a single station POFA is completed, aprintout of the results is produced. To analyze thisprintout properly, the technician must understand

Figure 5-1.—Single station POFA configurations.

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what equipment is being tested. The configuration inwhich the POFA was run determines some of theequipment being tested. The POFA can be run in twoconfigurations, as shown in figure 5-1.

In the full configuration, the single station POFAwill test the following areas:

CDS compute r I /O channe l in te r rup trecognition and acceptance

Security device I/O path

Data terminal transmit and receive registers,multiplex and demultiplex, and transmit andreceive sequence operations

Switchboard integrity

DTS-to-radio and radio-to-DTS audio path

Capability of the HF radio set to develop andaccept sidebands (both transmit and receive).

By studying the above list, you can see that mostnormal link operations are tested during a singlestation POFA. Certain functions, however, are notchecked by running a single station POFA. The DTSuses the transmit timing as the reference for the entiretest; therefore, the receive timing circuitry is notchecked. Also, certain other functions, such asDoppler correction, are not checked.

The printout generated at the end of a singlestation POFA lists interrupt status, illegal interrupts,parity, and bit-by-bit word errors. A single stationPOFA should always produce a totally error-freeprintout. However, when a printout with errors isreceived, the technician needs to be able to analyzethe error package effectively.

The interrupts, for example, must occur in thefollowing sequence:

Prepare to transmit

Prepare to receive

End of receive

If you receive interrupts in any other order, such astwo consecutive prepare to transmit interrupts or anend of receive before the prepare to receive, an errorcondition exists.

The parity should always equal zero. As youlearned in the previous chapter, the parity, or errordetection status bits, indicates an error has beendetected in the received data. When errors aredetected, they are listed in the bit-by-bit section of theprintout.

Even if the printout indicates a few random biterrors, this condition should not be ignored. Randombit errors can be caused by several areas in the system,including the CDS computer, the data switchboard, orthe DTS. You can narrow down to the exact areacausing the problem by running the POFA in severalconfigurations. Changing computers and cryptodevices can aid you in determining the malfunction.

Because of the unique function of the cryptodevice, a single broken line in the switchboard couldcause all the bits to be randomly picked up orrandomly dropped. When the broken wire is on theencrypted side of the switchboard, the crypto devicereads the state of that line during the decryption cycleand the entire decryption cycle is changed.

MULTI-STATION POFA

The multi-station POFA is a test of the Link-11system that involves more than one platform.Because this POFA most closely represents normallink operations, more equipment is tested. The multi-station POFA is run in the Roll Call mode using a setof known data words. Figure 5-2 shows the data flowfor a multi-station POFA. A designated unit transmitsa block of 230 data words that are received by theother platforms involved in the multi-station POFA.The receiving computer(s) compare(s) the data againstthe known pattern, count(s) the words in error, andsend(s) this count back to the original ship. Thistransmission is known as the error status report.Ideally, the multi-station POFA should run error-free.

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Figure 5-2.—Link-11 multi-station POFA data flow.

Multi-Station POFA Procedures

The procedures for running a multi-station POFArequire coordination of all participating units. For thisto be a good test, all units must be positioned within25 miles of each other. This is usually coordinated bythe Link-11 manager in conjunction with the battlegroup commander.

Just before the time the multi-station POFA is tobe conducted, NCS should end the operational linkand direct all stations to run a single station POFA.The picket station reports back to NCS when thesingle station POFA has been completed. The picketstation will also report the status of the single stationerror printout. Any errors noted during single stationPOFA should be corrected before the multi-stationPOFA, or the station experiencing errors should notbe included in the multi-station POFA.

The multi-station POFA should be run using thesame frequency as the current operational frequency.After running the single station POFA, NCS shoulddirect all participants to go to Radio Silence. Duringthis time, all stations should monitor the assignedfrequency for noise. The frequency can be monitoredthrough the headphones or by using a frequencyanalyzer. A noisy frequency can cause errors in themulti-station POFA. If the frequency is too noisy,consider using an alternate frequency.

Once the frequency has been checked, NCS willtell all participants to prepare to receive POFA. Afterall stations report that they are ready, NCS initiatesthe POFA. All stations monitor the POFA, and check

the control panel of the DTS for errors. After aminimum of 5 minutes, NCS terminates the POFA.

When the POFA is terminated, a printout isgenerated. The final step in running a multi-stationPOFA is the analysis of the printout.

Analyzing Multi-Station POFA Results

R u n n i n g a m u l t i - s t a t i o n P O F A c l o s e l yapproximates actual link operating conditions. Toanalyze the printout fully, the technician needs to beaware of some of the factors that can affect linkoperations.

When the printout is completed, the analysis iseasier to complete if the technician records thefollowing information on the printout:

Which station is NCS

Dis tance and re la t ive bea r ing o f a l lparticipating units

Frequency used

Frequency quality

Equipment used (radio, trunk line, computer,crypto, etc.)

Start and stop time of the POFA

The printout will contain a summary of theactivity that includes the time, in minutes andseconds, that the station was on the air, the totalnumber of words transmitted, the total number ofwords received, and the total number of words witherrors. This information can be used to calculate thelink quality factor. To calculate the link qualityfactor, divide the number of words received by thenumber of words transmitted. When the quotient isgreater than 95 percent but less than 100 percent,consider the POFA successful.

Next, compute the receive error factor. Ideally,the POFA should run with zero errors. Since themulti-station POFA is transmitted, atmospheric

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interference, ship’s position, antenna location, andEMI are just a few of the things that can induce errorsin a radio signal. Determine the receive error factorby dividing the number of words with errors by thenumber of words received. When the receive errorfactor is less than 1 percent, consider the POFAsuccessful.

When the printout indicates that data was receivedfrom an unrecognized station (UNREC STA), thetechnician should check the number of wordsreceived. The multi-station POFA transmit bufferconsists of 230 words. One buffer of 230 words froman unrecognized station is acceptable and generallydoes not indicate a problem. More than one buffermay indicate a problem, but multiple buffers from anUNREC STA can also be caused by interference onthe frequency.

The printout will also indicate the parity status ofthe words received in error. During the POFA, sincethe computer knows the contents of the received datablock, it performs a parity check on all receivedwords. These parity checks are compared with theparity status received from the DTS. The printoutindicates these parity checks. The heading PARITYSTATUS OF ERROR WORDS lists the number oferror words detected by the DTS and the parity (1, 2,o r 3 ) . T h e h e a d i n g P A R I T Y S T A T U S O FCORRECT WORDS indicates the computer paritycheck of words received as correct from the DTS.When an error is detected, the number of words inerror for each of the three parity status conditions arelisted here. The final part of the printout indicates theremote station reports. These reports are sent by otherstations as part of the data transferred during thePOFA.

Since a multi-station POFA is subject to varioustypes of interference, both natural and man-made,several attempts may be required for you to achieveacceptable results. Shifting NCS and repositioningthe ships are just two of the actions that couldcontribute to achieving a successful multi-stationPOFA.

THE LINK-11 MONITORINGSYSTEM (LMS-11)

“The link is down” is a statement that can strikefear into even the most seasoned technician. As wehave seen, the operation and maintenance of a high-quality link can be affected by many factors. Foryears, operators and technicians commonly blamedeach other for poor link operations. Some typicalLink-11 problems are as follows:

Participating units (PUs) not responding tocall-ups

Garbled data

The link goes completely dead, normaloperation ceases

Inability to establish a net

Excessive net cycle time

When such a problem occurred, the Link-11technician would run a single station POFA anddeclare that the DTS was sound and it must be theother ship, a poor frequency, or an operator error. Theoperator would blame the frequency or NCS. Otherunits would say the problem was another platformjamming the entire net. Typical strategies used tos o l v e l i n k p r o b l e m s u s u a l l y b e g a n w i t h arecommendation to change frequency. When thisstrategy failed to solve the problem, the next step wasto change NCS. If the problem still existed, then NCSwould eliminate PUs from the net, one at a time untilthe problem unit was identified. All of these actionstook time and were hit-and-miss techniques. Thistendency of trial-and-error troubleshooting andpointing fingers defined the need for a reliable visualsystem of monitoring the Link-11 network.

This need was filled with the development of theLink Moni to r ing Sys tem, AN/TSQ-162(V)1 ,commonly called the LMS-11. The LMS-11 providesan operator or a technician with a real-time visualdisplay of the Link-11 network while it is operating.

The LMS-11 is capable of measuring anddisplaying link signal data for the network as a whole,

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as well as for individual units. It can be used forperiodic equipment checks or for continuousmonitoring to determine the condition of all membersof the net.

LMS-11 SYSTEM CONFIGURATION

T h e L M S - 1 1 c o n s i s t s o f t h r e e g r o u p sequipment: a data processing group (DPG), acontrol/display group (CDG), and an accessory group(AG). The LMS-11 is shown in figure 5-3.

The LMS-11 is designed to be portable, and theequipment is installed in three carrying cases. Theequipment cases that house the electronic units of theDPG and CDG provide isolation from shock andvibration. The CDG is designed to be mounted on theD P G c a s e s . F o u r l a t c h e s f a s t e n t h e t w ounits together and provide a desk height, self-contained workstation. The system printer, which ispart of the accessory group, is mounted on the top ofthe CDG equipment case. When the LMS-11 isinstalled, the accessory group case provides storagefor the DPG and CDG equipment case covers. TheLMS-11 is normally located near the data terminal set,but it may be installed anywhere near a 600-ohmLink-11 audio signal.

Data Processing Group

The equipment required for the LMS-11 toreceive, sample, and process Link-11 audio signals iscontained in the data processing group. The DPG alsoprovides power control and distribution to the CDGand accessories. The DPG consists of the followingequipment:

The control processing unit

The audio interface unit

The dual 3.5-inch floppy disk drive unit

T h e p o w e r c o n t r o l u n i t

CONTROL PROCESSING UNIT. — T h econtrol processing unit consists of the HP9920U

Figure 5-3.—The LMS-11.

computer with an additional 2 MB of ram andassociated circuit card assemblies (CCA). Thesecircuit cards include the following:

Color output CCA

Composite Video CCA

Data communications interface

HP interface bus (HP-IB)

Analog-to-digital converter assembly

Fast Fourier Transform (FFT) processor

The color output CCA and the composite video CCAprovide the necessary signals to drive the colormonitor. The data communications interface providesan RS-232C asynchronous serial interface for thecolor printer. The HPIB is used to interface thesystem keyboard and the dual disk drives to the computer.

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Figure 5-4.—The LMS-11 keyboard.

The analog-to-digital converter converts theLink-11 audio signal into a digital signal for use bythe LMS-11. This digital signal is then transferred tothe computer where the FFT converts it to a frequencydomain. The Fast Fourier Transform consists of acomplex mathematical formula used to determine thephase shift of a signal.

AUDIO INTERFACE UNIT. —The audiointerface unit connects the upper sideband (USB) andlower sideband (LSB) audio signals from an HF radioor the USB from a UHF radio to the LMS-11. Theaudio signals are input to the analog-to-digitalconverter of the control processing unit. The audiointerface unit does not add a load to the audio signal.

DUAL 3.5-INCH FLOPPY DISK DRIVEUNIT. —The dual 3.5-inch floppy drive unit is usedto load the LMS-11 programs and to record Link-11data. The disk drives use 788 Kbyte, double-sided,double-density disks.

POWER CONTROL UNIT. —The powercontrol unit provides the control, distribution, andconditioning of the 115 VAC input power.

Control/Display Group (CDG)

The CDG consists of a color graphics monitor anda keyboard. The monitor displays operator-entereddata and system operation. The keyboard provides theoperator interface with the LMS-11.

COLOR DISPLAY MONITOR. —The colordisplay monitor is capable of displaying bothcomposite and RGB video. The computer generatescomposite video during the start-up and testing of theLMS-11. The RGB input with an external sync isused for displaying graphics during normal LMS-11operations. The monitor is also equipped with aspeaker and audio input to provide the operator withthe capability of monitoring the Link-11 audio signal.

KEYBOARD. —The keyboard is mounted on atray under the monitor. Under the tray, there is a

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storage slot for the LMS-11 technical manual. Thefunctional keys on the keyboard are color-coded tofacilitate operator selections and entries. The LMS-11keyboard is shown in figure 5-4.

Many of the keys on the LMS-11 keyboard are notused and the software does not recognize these keys.The actual functions of the keys are covered later inthis chapter.

Accessory Group (AG)

The accessory group contains a color graphicsprinter and spare parts and supplies for the LMS-11.The shipping container is also used to store the DPGand CDG container covers when the printer isremoved and mounted on the LMS-11. The colorgraphics printer is used to provide hard-copy printoutsof the display screen on plain paper or cleartransparency material.

LMS-11 OPERATION AND DISPLAYS

The LMS-11 provides real-time monitoring ofLink-11 operations. Problems with the net can beeasily detected in real time and you can determine thecause of the problems by evaluating the differentdisplays. When the cause is determined, the operatoror technician can take corrective action.

System Initialization

When the LMS-11 is turned on following thecorrect power-up sequence, the computer runs a groupof self-tests and it then boots the disk in drive 0.When the booting is complete, the LMS-11 monitordisplays the following message: “ B O O T I N GCOMPLETE, SWITCH TO RGB.” At this time,the operator should depress the RGB button on themonitor. The Initialization display is the first screendisplayed after the software is loaded. The operatorcan also recall the Initialization display by pressingthe INIT button of the keyboard. The Initializationdisplay screen is shown in figure 5-5.

During the initialization process, the operator isrequired to enter the following Link-11 operatingparameters:

DATE and TIME.

PRINTER. Selects which printer, if any, isbeing used with the LMS-11.

NET-MODE. Selects the Link-11 mode: NetSync, Net Test, Roll Call, Broadcast, or ShortBroadcast. The default is Roll Call.

DATA RATE. Selects whether the link isoperating in the fast or slow data rate.

FREQ-CORR. Enables or disables Dopplercorrection.

CALL-TIMEOUT. Allows the operator tospecify the number of frames for the missedcall timeout. Normal link operations is 15frames but is increased to 127 frames forsatellite link operations.

When all the required data is entered, the operatorshould select the desired mode of operation for theLMS-11. The five on-line modes are as follows:LINK MONITOR, NET, PU, SPECTRUM, andCARRIER SUPPRESSION.

Each mode has a unique display screen. Alldisplay screens consist of the following three parts:the header, the link signal or information area, and thestatus display. The header is at the top of the screena n d i n d i c a t e s t h e m o d e b e i n g d i s p l a y e d .information area is the middle section of the display,and the status display is at the bottom of the screen.The status display is the same for all on-line modes.

Link Monitor Mode

The link monitor mode display reflects linkactivity in real time. This display allows the operatoror technician to monitor link operations and detectproblems as they occur. To select the link monitormode, the operator presses the function key labeledLM. The link monitor mode display is shown infigure 5-6.

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Figure 5-5.—The LMS-11 Initialization display screen.

The top lines of the link monitor display screen report ends with the interrogation of the next PU incontain the header information. The LMS-11 mode isin the top center. The link mode is centered just underthe LMS-11 mode. In figure 5-6, this is RC FAST.This means the link is in Roll Call mode, fast datarate. The right side of the header displays the date andtime. The left side of the header information allowsthe operator to enter the NCS address and thesideband to monitor. The LMS-11 uses the address 77 as a default for NCS. However, recall fromchapter 2, that 77 is an illegal address and would notbe used in an active link. Since NCS never sends aninterrogation to itself, the LMS-11 uses this address todesignate NCS.

The display sweeps from left to right and from topto bottom. The display is color-coded and uses astair-step pattern that is easy to understand. Thedisplay of a single NCS report and the meaning of thecolors and levels is shown in figure 5-7. Figure 5-8shows how the different messages appear on theLMS-11 link monitor screen. Note that the NCS

the polling sequence.

Figure 5-6.—The link monitor display screen.

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Study figure 5-6 again and follow the pollingsequence of the four units in the net. The last reporton the top line is an NCS report and call to PU 04.This is followed by PU 04’s response on the left sideof line two. Next, PU 56 is called and responds witha picket reply. Upon completion of PU 56’s reply, PU64 is called. After 15 frame times without a response,PU 64 is called again. PU 64 appears to haveresponded to the second call, but the LMS-11 onlyrecognized the five preamble frames.

By using the link monitor display, the operator ortechnician can make sure the connectivity has beenestablished and that all the correct PUs are beingpolled and are responding.

Figure 5-6 also shows several problems thatcommonly occur during Link-11 operations. Noticethat PU 64 sometimes responds to the first call-up,sometimes to the second call-up, and sometimes PU64 does not respond at all. PU 56 responds all thetime except for the call-up at the end of line two andbeginning of line three. On line six there is a doubleresponse, or echo, from PU 04. If you were toexamine this particular sequence using the frame-by-frame analysis, you would find the PU 04 was calledagain. This indicates the NCS did not receive thereport from PU 04 and repeated the call-up during themiddle of the response.

Figure 5-8.—Link-11 messages as displayed by theLMS-11 link monitor mode.

Status Display

As shown in figure 5-9, the status display is at thebottom of each of the LMS-11 display screens. The

status display consists of the status box and two linesof information just above the status box. The top line,with the heading “XMT-ADDRS:” displays theaddresses of all PUs in the order they are being polled.The operator can monitor the polling in real time. Thedisplayed addresses change colors to indicate theirstatus. If the address is yellow, it is currently beinginterrogated. The yellow address turns green whenthe start code is received. The yellow address turnsred when the PU has been interrogated twice and noresponse is received.

The line under the “XMT-ADDRS:” is used todisplay system messages and LMS-11 alerts. Alertsare displayed on the left side of this line. Systemmessages are displayed on the right side of the line.

The status box provides the operator withinformation about signal processing, link activity, and ,raw recording of link data. Just below each of theframe types, a small green box, or light, appears toindicate the type of frame being processed. Thesesignal processing status indicators are not displayed inreal time. They are updated approximately every 50milliseconds. The signal processing indicators are asfollows:

Figure 5-7.—The link monitor display pattern.

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Figure 5-9.—The LMS-11 Status display.

LMS —Should always be green.

LSN —Indicates that the LMS-11 is listeningfor the link audio.

PRE —Indicates that a preamble has beendetected.

PHA —Indicates that a phase reference framehas been detected.

CC1 —Indicates the first frame of a controlcode.

CC2 —Indicates the second frame of a controlcode.

EOT —Indicates that the LMS-11 has detectedthe end of transmission.

NOIS —Indicates that the received data framedid not pass the data quality test.

DATA —Indicates that the LMS-11 hasdetected a data frame that has passed thequality test. Note that the control codes andphase reference frames are also data frames.

REC —Shows the status of the raw recordfunction of the LMS-11. The indicator will begreen when the recording is turned on and redwhen the recording is stopped.

The last two fields of the status box indicate theperformance of the net. The “%DATA:” field will befollowed by a number representing the percentage ofnet cycle time message data is transmitted with noerrors. The “NCT:” displays the net cycle time inseconds. Net cycle time is the time required for one

completed polling of the net. It can be measured fromcontrol stop to control stop from NCS, or the operatorcan specify a PU as the reference for net cycle time.The operator can also specify the number of cycles touse to determine net cycle time. The operator makesthese entries using the summarize parameter in theNET DISPLAY mode.

Net Display

The Net Display mode is activated when theoperator presses the NET key on the keyboard. TheNet Display mode presents the following two separatetypes of information: a Net Summary (summarizemode) or a PU History (history mode). In the NetSummary mode, the Net Display presents a summaryof quantitative information about the performance ofup to 21 PUs. In the PU History mode, the LMS-11displays data for a selected PU. The most recent 21transmissions of the specified PU will be displayedwhile in the PU History mode.

The Net Display mode is only available when thelink is in the Roll Call mode. Figure 5-10 shows ascreen for the Net Display in the Summarize modeand figure 5-11 shows the screen for a PU Historymode.

After the operator enters the Net Display mode,there are four operator entries that can affect theinformation and how it is displayed. These are NCS,PU, SIDEBAND, and SUMMARIZE. All of theentries are displayed as part of the header of the NetDisplay screen. The NCS, PU, and SIDEBANDfields are on the left side of the screen, and theSUMMARIZE field is on the right side of the screenjust below the date and time fields.

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Figure 5-10.—The LMS-11 Net Display in Summarize Mode.

NCS. —The NCS field allows the operator todesignate the PU number of the NCS. When anumber is not entered in this field, the default addressof 77 is used. It will also be used as the PU number inthe polling display of the status area and in the PUfield of the Net Display.

PU. —The PU field is used by the operator todesignate the PU whose recurring transmission is usedto define a cycle. The PU field works with theSUMMARIZE field.

SIDEBAND. —The SIDEBAND field allows theoperator to designate which sideband (USB, LSB, orDIV) is used for the information displayed.

SUMMARIZE. —The SUMMARIZE fieldenables the operator to designate the number of cyclesover which the summary is computed. A “cycle” isdefined as the recurring transmission from thedesignated PU. The data is tabulated after the

specified number of transmissions are received fromthe designated PU or after 200 transmissions arereceived by any station, whichever occurs first. TheSUMMARIZE field is also used to enable the PUHistory mode. The PU History mode is entered whenthe operator enters a zero in the summary field. Whenthe PU History mode is enabled by the operator, theword HISTORY is added to the Net Display title.The PU History mode display updates one line of dataimmediately after the specified PU has completed itstransmission.

The information displayed by the Net Displaymode is described in the following paragraphs.

PU. —The PU number. The first number listed isthe NCS, which has a default number of 77, or theaddress entered in the NCS field. The rest of the PUsare listed in numerical order.

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Figure 5-11.—The LMS-11 Net Display in PU History Mode.

SIG PWR. —The total signal strength of the 16tones, measured in dBm. A value of -51 indicates thatno signal was received.

SNR. —The signal-to-noise ratio, as measured indB. The SNR is calculated as the average power inthe data tones divided by the average power in thenoise tones. The LMS-11 can measure a SNR of near34 dB. A number preface by the greater than symbol“>” indicates that the average power in the noise toneswas below the measurable threshold. In this case, thenumber represents the data tone signal strength only.An SNR value of 30 or higher is considered excellent.An SNR value of less than 10 is unusable.

FRAME CNT. —A count of all data framesreceived over the specified number of cycles. Dataframes include the phase reference frame and controlcode frames in each message. A value that isfollowed by a “?” and color-coded yellow is displayedif the frame count of a picket station average is lessthan or equal to six frames. The two start code

frames, the phase reference frame, the crypto frame,and the two stop code frames would account for thesix frames. Therefore, if a picket unit transmits six orless frames, no actual message data is being receivedand may indicate a problem with the computer or DTSof the unit. A yellow color-coded value followed bythe “?” is added for an NCS when the number offrames is equal to or less than eight. The twoadditional frames account for the next station addressat the end of an NCS report.

PERCENTAGE THROUGH. —The %THRUcolumn is a number that indicates the percentage ofmessage data that is received error-free. thepercentage is found by comparing the number oferror-free message data frames with the total number of message data frames received.

CF. —This is a percentage of control code failures.A PU with strong signals that never misses a call willhave a 0 % code failure. A PU that never answers,such as a dummy PU, will have a 100 % code failure.

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Figure 5-12.—The LMS-11 PU Display mode.

Values between 1 and 100 could be due to noise or PHASE ERR M. —This is the mean, or average,

weak equipment or an equipment malfunction.

BER. —This is the bit error rate measured as thenumber of bit errors per 1,000. Bit errors increase asthe signal-to-noise ratio decreases. A bit error ratethat exceeds a theoretical value for a given SNR isindicated by displaying both the BER and SNR inyellow.

REL 605. —This column indicates the relativepower of the 605-Hz tone with respect to the averagepower of the 15 data tones, measured in dB. It shouldbe +6 dB.

VAR DATA. —This is the variation of power inthe data tones in dB. The relative power of each ofthe data tones, with respect to the average power ofthe data tones, is determined. The variation is thedifference between the maximum and the minimum.Under ideal conditions, the variation is zero. TheTADIL A specification for maximum variation is 1.5dB.

phase error of the data tones. The intelligence-i sstored in the data tones by use of the phase differencesthat are odd multiples of 45 degrees. If the phasedifference of a data frame is 50 degrees when theexpected difference is 45 degrees, the error would be5 degrees. The phase errors for each tone are addedup, and after the specified number of cycles, the sumfor each tone is divided by the number of frames toobtain the mean phase error for each tone. The meanphase error for all 15 tones is then summed anddivided by 15 to obtain the value displayed.

PHASE ERROR SD. —This is the standarddeviation of the phase error in all 15 tones.

RFE/DS. —This is the radio frequency error, orDoppler shift, measured in Hertz. If the Dopplercor rec t ion was enab led dur ing the LMS-11initialization, the value is color-coded green. If theDoppler correction is turned off, this value is color-coded cyan.

NCT. —This is the net cycle time, as measuredfrom phase reference frame to-phase reference frame,

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of the reporting unit. Note that this measure of netcycle time is different from that used in other NCTcalculations.

PU Display

The PU display shows detailed information aboutthe signal received from the specified PU. The PUdisplay can operate in broadcast, short broadcast, andRoll Call modes. In Broadcast and Short Broadcast,the display is updated after every transmission. InRoll Call mode, the display is updated after thespecified number of net cycles or 200 transmissions,whichever occurs first. When the net cycles are set tozero, the display updates immediately after thedesignated PU has transmitted. The PU display isshown in figure 5-12.

The PU display is activated when the operatorpresses the PU function key on the keyboard. Theinformation in the PU display is presented in two bargraphs with additional amplifying information justunder the bar graphs. In the PU display header, theoperator enters the address of NCS (or 77), theaddress of the unit to be evaluated, the sideband to beevaluated (USB, LSB, or DIV), and the number ofcycles to summarize for the display. The followingparagraphs describe the information presented in thePU display.

RELATIVE POWER (dB). —This bar graphdisplays the relative power in each of the Link-11tones. The relative power is calculated with respect tothe average of the data tones. The expected valuesshould be +6 dB for the 605-Hz tone (tone 5) and 0dB for the data tones. The TADIL A specificationsallow for a difference of 1.5 dB between themaximum and minimum power levels of the datatones. A noisy signal may cause the power levels ofthe data tones to deviate considerably from thestandard. The bar graph for relative power is alsocolor coded. When the relative power of a data toneis ±1 dB, the bar is green. If the power level is in therange of +1 to +2 dB or –1 to –2 dB, the bar will beyellow. The bar is red if the power level is greaterthan +2 dB or less than -2 dB. The length of the barsplotted on the graph is rounded off to the nearest 1/2dB.

PHASE ERROR (DEGREES). —The phaseerror (degrees) bar graph shows the mean and thestandard deviation of the Link-11 tones. The standarddeviation of a tone is plotted by a color bar on thegraph. The size of the color bars is plotted to thenearest whole degree of deviation. The meandeviation of the tone is indicated by a small whiteline, usually in the center of the standard deviationcolor bar. The mean phase error should fall between+45 degrees and -45 degrees. If the data is bad, themean phase error is set to -45 degrees and thestandard deviation is set to 90 degrees. This causesthe bar to be drawn across both quadrants of thegraph.

The standard deviation is represented by a color-coded bar for each tone. A green bar is displayed ifthe s tandard deviat ion is within 10 degrees.Deviations between 10 degrees and 20 degrees arerepresented by a yellow bar, and deviations greaterthan 20 degrees are red. The standard deviation mustbe a positive value that is less than 45 degrees. If thestandard deviation is out of range for a given tone, thedata is bad. This condition is indicated by theLMS-11 by setting the mean deviation to 45 degreesand the standard deviation to 90 degrees. As with themean deviation phase error, this causes the bar to bepainted in both quadrants of the graph.

Some causes o f phase e r ro r s a re no i se ,simultaneous transmissions, poor framing, and errorsin Doppler correction due to noise on the preamble.For example, a picket unit transmitting Net Syncduring Roll Call will cause an error condition. Theexpected value of the mean deviation is 0 degreeswith a standard deviation of ±5 degrees. If only onetone has a mean value that is greatly different from theother tones, it may be an indication of a frequencyerror on that tone.

SIGNAL POWER. —The signal power is part ofthe amplifying information under the two bar graphs.The signal power is the total signal strength in the 16tones. It is measured in dBm. If no signal is received,the default value of -51 dBm is listed.

SNR. —This is the signal-to-noise ratio. It ismeasured in dB and calculated as the ratio of the

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average power in the data tones to the average powerin the noise tones. If the SNR value is preceded bythe symbol “>,” it indicates that the average power inthe noise tones is below the measurable threshold andthe actual SNR is greater than the value indicated.The maximum value that the LMS-11 can measure isabout 34 dB. An SNR that is greater than 30 dB isexcellent. If the SNR is less than 10 dB, the data isunusable.

BER. —This is the bit error rate per thousand.The incidence of bit errors increases as the signal-to-noise ratio decreases.

MISSED CODES PERCENTAGE. —This is apercentage of each type of code that is missed. Thenumber of codes (start, stop, and address call-ups)missed and received is tabulated and the percentage ofeach type missed is calculated.

FRAMES. —This is the total number of dataframes received, including the phase reference andcontrol code frames.

CS. —This field displays the carrier suppressionvalue of the upper and lower sidebands as a ratio ofthe power in the 605-Hz to the power of the carrierfrequency. The value display is measured in dB.

RFE/DS. —The radio frequency error or Dopplershift of the received signal in Hertz. The display iscolor-coded cyan if frequency correction was disabledduring LMS-11 initialization.

Spectrum Display

The spectrum display graphically shows the powerlevels of all the Link-11 tones and the noise tones thatare the odd harmonics of 55 Hertz. The spectrumdisplay screen is shown in figure 5-13. The x-axis ofthe bar graph is numbered from 1 to 30 to represent 30tones. Tone 05 is the 605-Hz Doppler tone. Tones 8through 21 and tone 26 are the data tones. Theremaining tones are not used by the Link-11 systembut are sampled and displayed to give the operator anindication of the noise level.

The y-axis of the bar graph displays the relativepower of each tone in dB. The highest value of thescale is 0 dB and decreases to -40 dB. The tone withthe greatest amount of power is set to 0 dB on thescale. This should be the 605-Hz tone. Theremaining tones are measured relative to the tone withthe greatest power. A single blue line is drawnhorizontally across the screen at the -6 dB level.Ideally, all data tones should extend up to this line.

The 605-Hz tone and the data tones are displayedby solid green vertical lines. If the power of a datatone is greater than -6 dB with respect to the 605-Hztone, the area above the -6 dB line is indicated by anopen yellow bar on top of the green bar. If the powerlevel of a data tone is below the -6 dB threshold, anopen yellow bar is used to fill in the remainingdistance. This allows the operator to view the effectsof the noise. The power of the noise tones is alsoindicated by open yellow bars.

To enter the spectrum display, depress the SPECTkey on the keyboard. Several options are available tothe operator by entering data into the header fields ofthe spectrum display. The operator may designate theaddress of the NCS. The default address is 77. Theoperator can also select a particular sideband (USB,LSB, or DIV) for display. By using the RESTRICTfield, the operator can restrict the display to only dataframes or only preamble frames, or choose norestrictions. The PU field allows the operator todesignate a particular PU for display. If 00 is enteredinto the PU field, then the data display is continuouslyupdated with samples from the entire net.

Carrier Suppression Display

The carrier suppression display measures howsuccessfully the carrier frequency is suppressed. Thecarrier suppression measurements can only be madeduring Net Sync. To measure the carrier suppression,the radio must be off-tuned by -500 Hz for the uppersideband and +500 Hz for the lower sideband. Thisoff-tuning allows the program to measure andcompare the relative power of the carrier frequencyand the 605-Hz tone of the preamble.

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Figure 5-13.—The Spectrum Display screen of the LMS-11.

RECOGNIZING LINK-11 NET PROBLEMS

The LMS-11 is very useful in evaluating Link-11net quality. As you have seen, the various on-linemodes can help you determine various problems.These include a station that is consistently missingcall-ups, poor signal-to-noise ratio, and low powerfrom a unit. Some common Link-11 problems and theLMS-11 display are covered in the next fewparagraphs.

Figure 5-14 shows an example of how a PU notresponding to call-ups would appear on the LMS-11operating in the Link Monitor mode. When a PU doesnot respond to a call-up, the reason may be that theincorrect PU number was entered at the NCS or at theDTS of the unit. It can also be caused by a poorreceiver at the PU, causing the PU to not receive itscall-up. A third problem could be a weak transmitterat the PU, causing the NCS to not receive the responseand therefore, repelling the PU.

Figure 5-14.—A PU not responding to NCS call-up.

Figure 5-15 shows the display that appears whena PU is responding to NCS call-ups, but the reportcontains no data. Causes of this problem could be theKG-40 has an alarm, the CDS program is down, or theproblem is in the CDS computer to DTS patching.

Figure 5-15.—A PU responding with no data.

When NCS fails to receive a stop code from a PU,it causes a stoppage of the net, as shown in figure5-16. If this condition occurs repeatedly and can betraced to a single PU, the NCS should delete the PUuntil the stop code problem in the DTS is corrected.

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Figure 5-16.—A net stoppage caused by NCS not receivinga stop code.

Figure 5-17 shows several PUs not responding tocall-ups. Some of the causes for this condition couldbe the following: NCS having an incorrect PUaddress entered in the DTS, low transmitter power outfrom NCS, an excessively noisy frequency, or weakPU receivers.

Figure 5-17.—Several PUs not responding to NCS call-ups.

The LMS-11 also has several off-line modes thatallow you to save data onto a disk and analyze thedata in detail. The off-line modes include a frame-by-frame display to analyze each frame of a transmission.This allows you to analyze the data of a particular PUand shows the status of each bit position. Rememberthat when you are doing a frame-by-frame analysis,the data has not been decrypted.

More information on all modes of the LMS-11 canbe found the System Operation and MaintenanceInstructions, Organization Level, Link MonitorSystem AN/TSQ-162(V)1, EE-190-AB-OMI-010/TSQ-162(V)1.

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CHAPTER 6

LINK-4A

INTRODUCTION

The Link-4A system is a fully automatic, high-speed data transmission systemused for aircraft control. The system provides controlling information to the aircraft,using radio transmission between the controlling ship and the controlled aircraft. TheCarrier Aircraft Inertial Navigation System (CAINS) is also a part of the Link-4Asystem. The CAINS system is used to load alignment and way-point data into theaircraft on the flight deck or the hangar deck.

After completing this chapter, you should be able to:

. Describe the functions of the Link-4A system.

. Describe the operating modes of the Link-4A data terminal set.

. Describe the types of messages used by the Link-4A system.

. Describe the functional operation of the Link-4A data terminal

. Describe the test messages used in the Link-4A system.

LINK-4A SYSTEM OVERVIEW

The two major components of the Link-4A systemare the Link-4A CDS system and the CAINS system.Both systems use serial time-division multiplexing totransmit control and reply messages over a frequency-shift keyed (FSK) UHF radio communicationschannel. The CAINS system can also transmit datavia hard-wired stations on the flight deck or hangardeck.

LINK-4A CDS SYSTEM

The Link-4A CDS system is used to provide one-way or two-way communications between thecontrolling station and up to 100 controlled aircraft.The controlling station transmits to the aircraft controlmessages con ta in ing vec to r ing in fo rmat ion ,commands, and data pertaining to the target ordestination of the aircraft. The aircraft transmits replymessages containing information concerning itsheading, altitude, airspeed, and tactical readiness. Theaircraft control messages are developed by the CDS

computer using radar-derived target data, reply datafrom the aircraft, and other tactical data.

A typical shipboard Link-4A system configurationis shown in figure 6-1. It consists of the CDScomputer, a data terminal set, a communicationsswitchboard, and a UHF radio transceiver.

The CDS computer outputs parallel digital data tothe Link-4A data terminal set. Currently, the dataterminal set most shipboard installations use is a typeof the AN/SSW-1 (U). It will be designated as theAN/SSW-lA/B/C/D/E(U). The data terminal setconverts the computer data into a serial time-divisionmultiplexed pulse train that is transferred to the radiotransceiver through the communications switchboard.The communications switchboard connects theselected UHF transceiver to the data terminal set. Theradio transceiver converts the pulse train into FSKvariations in the carrier signal frequency.

After the aircraft receives the transmitted data, itmay respond by transmitting data to the controlling

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Figure 6-1.—The shipboard Link-4A CDS system.

station. This is the reception cycle. The receiverremoves the carrier frequency and forms the serialdata pulse train. The pulse train is sent to the dataterminal set via the switchboard. The data terminalset converts the serial pulse trains into parallel dataand sends the data to the CDS computer.

In a typical aircraft carrier system, the four distinctmodes of operation in the Link-4A system areintercept vectoring, air traffic control, automaticcarrier landing system, and precision course direction.

Intercept Vectoring

Intercept vectoring enables the controlling ship toguide an aircraft to an intercept point. The two typesof data sent to the aircraft during intercept vectoringare command data and situation data. Command dataprovides direct steering and control information,whereas situation data provides the aircraft with anoverall picture of the tactical situation with respect toits target.

This data is used to guide the aircraft withinstriking range of its target at optimum position andaltitude for an attack. The messages also containinstructions to the pilot, such as target identity, breakengagement, and return to base.

Air Traffic Control

In the air traffic control mode, Link-4A is used tocontrol the aircraft in the carrier’s traffic pattern. Thecontrol station transmits data to the aircraft tomaintain safe flight patterns and assigns priority forlanding approach. As each aircraft enters the landingpattern, it is transferred to the automatic carrierlanding system for final approach and landing.

Automatic Carrier Landing System

The automatic carrier landing system selectsaircraft in the order of priority from the pattern andenters them into the final approach. During the finalapproach, a precision radar tracks the aircraft. Correctinformation pertaining to the approach is transmittedto the aircraft’s autopilot. When conditions areunfavorable for a landing, the wave-off control isinitiated and the aircraft is guided through a shortpattern and the landing approach is repeated.

Precision Course Direction

The precision course direction mode is used in theremote guidance of bomber and reconnaissanceaircraft, and drones. The guidance messages containpitch, bank, heading, altitude, and airspeed commandsto permit very precise control of the aircraft’s flightpath.

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CARRIER AIRCRAFT INERTIALNAVIGATIONAL SYSTEM (CAINS)

The CAINS system is used to load alignment andway-point data into aircraft on the flight deck or thehanger deck. Aircraft alignment data consists oflongitude, latitude, and ship’s velocity data from theship’s inertial navigation system. Way-point data is aset of predetermined geographical points loaded intothe aircraft’s navigation computer. Way pointsprovide the aircraft with destination or targetinformation.

When the CAINS system is used, data can beloaded into the aircraft by either a hard-wired systemor RF radio transmission. The hard-wired insertion ofdata is accomplished when the aircraft is connected toa deck edge outlet box (DEOB). The pulse amplifiersof the AN/SSW-1D/E can provide outputs for up to40 of these DEOBs. After the initial data is loaded,the aircraft is disconnected from the DEOB, but itcontinues to receive alignment data until the launch.Then the aircraft system reverts to its original tacticalcondition.

LINK-4A MESSAGE FORMATS

The following are the three types of messagesused in the Link-4A system: control messages, replymessages, and test messages. These messages usetwo basic formats. Control messages are transmittedfrom the controlling ship to the aircraft. Replymessages are transmitted from the aircraft to thecontrol station.

The timing for Link-4A communications isdetermined from the duration of the transmit andreceive cycles. The standard CDS control messagesare 14 msec in duration, while the receive cycle forreply messages is 18 msec in duration. The CAINSsystem does not use reply messages; therefore, a 2msec receive cycle is substituted to allow time for theLink-4A data terminal set to initialize the nextmessage. Thus we have the following two timingcycles: 14/18 (control message 14 msec/receive cycle18 msec) and 14/2 (control message 14 msec/receivecycle 2 msec).

CONTROL MESSAGE FORMAT

Control messages are assembled and transmittedduring the 14-msec transmit frame. Figure 6-2shows the standard structure of a Link-4A controlmessage. During the transmit frame, the transmit keysignal and the control message pulse train are sent tothe radio set transmitter. The transmit frame isdivided into seventy 200 µsec time slots that containthe s y n c p r e a m b l e , the data bits , a n d t h etransmitter un-key signal.

Figure 6-2.—The Link-4A control message format.

Sync Preamble

The sync preamble is made up of the first 13 timeslots of the control message. The first eight time slotseach contain one cycle of a square wave, consisting of100 µsec in the “0” state and 100 µsec in the “1” state.These eight time slots are known as the sync burst.Following the sync burst are four time slots in the “0”state, called the guard interval. The guard intervalindicates the changeover to the 200-µsec data signals.Time slot 13 is the start bit and is always a “1.”

Data Bits

The Link-4A message data is contained in the 56time slots (slots 14 through 69) that follow the syncpreamble. Each time slot contains one data bit. Thefirst 13 bits of this data is a binary number thatindicates the address of the particular aircraft. Onlythe aircraft with this preassigned address willrecognize the message and act on the message data.Following the address is a five-digit label thatdesignates the type of data contained in the message.The labels correspond to the modes of operation. The

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last digit designates whether the message is an A or Btype. In most modes, both an A and a B type ofmessage are required to transmit all the necessary datato the aircraft. The remaining data bit time slotscontain the various control commands.

Transmitter Un-key Signal

The last time slot (slot 70) is a 200-µsec periodallotted for transmitter turn-off time and does notcontain any data.

REPLY MESSAGE FORMAT

Reply messages are received during the 18-msecreceive cycle. The reply message contains a total of56 time slots and occupies a period of 11.2 msec.This 11.2-msec reply must be received during the18-msec receive cycle. This allows for a maximum of4.8 msec for transmission delay.

The reply message consists of a sync preamble,42-data bit time slots, and a guard interval, as shownin figure 6-3. The sync preamble is identical to thecontrol message sync preamble. The information inthe 42-data time slots is divided into groups of digitsthat identify the source and type of message, and themessage data. The last time slot is the guard intervaland it allows for transmitter turn-off time.

Figure 6-3.—The Link-4A reply message format.

TEST MESSAGES

During Link-4A operations the controlling stationsends test messages at periodic intervals to the dataterminal set for testing the message processing anddisplay circuitry of the aircraft being controlled. Thetest messages also check the data terminal set and itsinterfaces. The two types of test messages areuniversal test message (UTM) and monitor controland reply messages (MCM/MRM).

Universal Test Messages

Universal test messages (UTMs) are Link-4Acontrol messages that are always addressed to aparticular universal address and contain fixed, specificinformation in each data field. The UTMs provide thecontrolled aircraft with a means to verify properoperation of the link.

Monitor Control and Reply Messages

Monitor control messages (MCMs) are Link-4Acontrol messages that are sent to the data terminal setfrom the CDS computer to initiate internal testing ofthe data terminal set. After the data terminal setcompletes its self-check, the MCM is transmitted withthe universal address. Depending on the equipmentconfiguration of the aircraft, the MCM will either berejected or processed as a UTM.

The monitor reply message (MRM) is sent to theCDS computer upon the successful processing of theMCM. The MRM is effectively a return of the MCMdata content which indicates that the internal andinterface tests were successful.

THE LINK-4A SYSTEM COMPONENTS

The Link-4A system consists of the CDScomputer, a data terminal set, a communicationsswitchboard, and a UHF radio set.

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Figure 6-4.—The AN/SSW-1D/E data terminal set.

DATA TERMINAL SET AN/SSW-1D/E

The Link-4A data terminal set is theAN/SSW-lD/E. The data terminal set performs thefollowing functions:

Provides overall Link-4A system timing

Converts parallel data from the CDS computerinto serial data for transmission to controlledaircraft

Converts serial data received from controlledaircraft into parallel data for input to the CDScomputer.

The current five versions of the AN/SSW-1 usedin shipboard Link-4A systems are the AN/SSW-1A,1B, 1C, 1D, and 1E. The AN/SSW-1A, 1B, and 1Care operationally and functionally identical, as are theAN/SSW-1D and 1E. The major difference betweenthe two groupings of versions is the single-channelcapability of the AN/SSW-1A/B/C and the dual-channel capability of the AN/SSW-1D/E. Each of thedual channels is capable of the link operations of thesingle channel AN/SSW-1. The dual-channelAN/SSW-1D/E is also capable of transmitting CAINSdata. For purposes of this lesson, we use theAN/SSW-1D/E.

The AN/SSW-1D/E shown in figure 6-4, consistsof the following eight major subassemblies: onecoordinate data transfer control, two digital-to-digital converters, two monitor test panels, two

Figure 6-5.—The coordinate data transfer control assembly (AN/SSW-1D/E).

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pulse amplifier assemblies, and a power supplyassembly. There are two independent equipmentgroups in the AN/SSW-1D/E. Each group is capableof simultaneous operations with separate anddedicated computer input-output channels anddedicated UHF radio sets.

Coordinate Data Transfer Control

The coordinate data transfer control assemblyenables the connection of each of the digital-to-digitalconverters (DDC) to one of two different computers.The control panel for the coordinate data transfercontrol assembly is shown in figure 6-5. TheCOMPUTER SELECT provides switching, such thatDDC A is connected to computer 1 and DDC B isconnected to computer 2 or vice versa. Either of thetwo DDCs maybe connected to its monitor test panelfor off-line testing. The DDC output options are theCDS (old NTDS) radio set, the CAINS system, or thetest mode.

Digital-to-Digital Converter

The digital-to-digital converter assembly providessystem timing, converts parallel data from the CDScomputer into serial data for transmission by the UHFradio set, and converts serial data received from theradio set into parallel data for input to the CDScomputer. The DDC is the heart of the data terminalset.

Monitor Test Panel

The monitor test panel provides the technicianwith a means to monitor Link-4A operations and off-line testing capabilities. There is one monitor testpanel for each DDC.

Pulse Amplifier

The pulse amplifiers provide level and signalconversion functions to allow the AN/SSW-1D/E dataterminal set to drive the serial output for the UHFradio set and the deck edge outlet boxes for CAINS.

COMMUNICATIONS SWITCHBOARD

The communications switchboard interconnectsthe AN/SSW-1 to the UHF rad io se t s . Thecommunications switchboard is similar to the Link-11switchboard described in chapter 4 of this manual.

LINK MONITOR SYSTEM (LMS-4)

The LMS-4 provides stand-alone Link-4A monitorand readiness check capabilities, and its operation issimilar to the LMS-11 covered in the previouschapter. The monitor function listens passively to theLink-4A communications between the control stationand the controlled aircraft. Signal analysis and testmessage validity are performed on the data. Thereadiness check function tests the readiness of thecontrol station to conduct live two-way Link-4Aoperations. Control messages transmitted by thecontrol s tat ion are monitored and the LMS-4generates the reply messages required to maintaintwo-way communications.

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CHAPTER 7

NEW TECHNOLOGY IN DATA COMMUNICATIONS

INTRODUCTION

The current Link-11 and Link-4A systems are being updated with new equipments. The DataTerminal Set AN/USQ-125 is currently replacing the older Link-11 data terminals. In addition, newcommunications systems, such as the Command and Control Processor (C2P) and the JointTactical Information Distribution System (JTIDS), are quickly becoming commonplace onvarious platforms in the Navy. This chapter will introduce you to some of the changes taking placeand the basic features of some of the new systems.

After completing this chapter, you should be able to:

. Describe the various components of the AN/USQ-125 Data Terminal Set.

. Describe the operation of the AN/USQ-125 in a typical Link-11 system.

. State the purpose of the Joint Tactical Information Data System (Link-16).

. Describe the components of the Link-16 system.

. State the function of the Command and Control Processor (C2P) system.

l Describe the components of the C2P system.

THE AN/USQ-125 DATA TERMINAL SET

The AN/USQ-125 data terminal set is the newestLink-11 data terminal set in the Navy. It is quicklyreplacing older DTSs, such as the AN/USQ-36 andthe AN/USQ-59. There are several configurations ofthe AN/USQ- 125. The CP-2205(P)(V)/USQ-125 dataterminal with the MX-512P/RC Remote Control Unitc o n f i g u r a t i o n . T h e o t h e r c o n f i g u r a t i o n i sCP-2205(P)(V)2/USQ-125 data terminal with apersonal computer (386 or better) running theMXPCR software. The personal computer serves the Figure 7-1.—The AN/USQ-125 data terminal set standardsame function as the remote control indicator in this interface block diagram.

configuration. The standard interface configuration ofthe AN/USQ-125 is shown in figure 7-1. In thischapter, we examine the data terminal and the THE CP-2205(P)(V)/USQ-125 DATA TERMINALfunctions of the control indicators, either theMX-512P/RC or a personal computer. The CP-2205(P)(V)/USQ-125 data terminal is a

compact, state-of-the-art data terminal that is mountedin a standard 19-inch equipment rack. The data

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Figure 7-2.—The CP-2205(P)(V)/USQ-125 data terminal block diagram.

terminal has the following three major components: aprocessor board, a CDS interface board, and thepower supply. Figure 7-2 is a block diagram of theCP-2205(P) (V) /USQ-125 da ta t e rmina l . Theprocessor board performs modulation/demodulationand error detection and correction, and provides theinterface with the radio set. The CDS interface boardprovides the interface with the CDS computer. TheCP-2205(P)(V)/USQ-125 data terminal performsmany of the same functions as previous Link-11 dataterminal sets. These functions include the following:

Data conversion

Data error detection and correction

Control code generation and detection

Synchronization

Encryption device data transfer

Computer and radio control signals for two-way Link-11 data transfers

In addition, the CP-2205(P)(V)/USQ-125 data

terminal provides the following new features:

Both multi-tone and single-tone waveformoperations

Enhanced Link Quality Analysis (ELQA)

Maximum useable frequency (MUF) option

Multi-Frequency Link

On-line and Off-line System Test Options

Multi-Tone Waveform Link

Multi-tone link operations are basically the sameas in the previous Link-11 data terminal sets and arecalled conventional Link-11 waveforms. The dataterminal generates the 605-Hz Doppler tone and 15data tones. The frequencies of the data tones are thesame as described in chapter 4. Message formats andmodes are also the same.

Single-Tone Waveform Link

Single-tone waveform link updates the 1960’stechnology used in data communications. The single-ton waveform is a 1,800-Hz phase-modulatedwaveform containing the Link-11 data in a serial bitstream. The single-tone waveform is most commonlyused with the wire-line option of the USQ-125 dataterminal. The CP-2205(P)(V)/USQ-125 data terminalwire-line option provides an interface port that can beused with a standard wire-line or a satellite modem.Using this option expands the means in which Link-11 data can be exchanged, overcoming the limitationsof the traditional UHF and HF radio links.

Enhanced Link Quality Analysis (ELQA)

The Enhanced Link Quality Analysis option of thedata terminal incorporates almost all of the functionsof the LMS-11. This allows the operator to monitorand evaluate the performance of the link net.Information that can be displayed includes the

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following: sideband power, error rate, and percentageof interrogations answered.

Maximum Useable Frequency (MUF) Option

The maximum useable frequency option is aroutine that calculates the optimum frequency forLink-11 operat ions. This routine calculates afrequency for each hour of the day based ongeographic location, the range of other participants inthe net, and sunspot activity.

Multi-Frequency Link

The multi-frequency link option improves currentlink operations. by simultaneously using fourfrequencies. The normal configuration for multi-frequency link operations uses three HF and one UHFfrequency. To implement this option, three additionalprocessor boards are installed in the data terminal.Each data terminal board is connected to a separateradio, as shown in figure 7-3.

Figure 7-3.—Block diagram of the AN/USQ-125 dataterminal configured for multi-frequency link operations.

During the Link-11 receive cycle, each dataterminal board demodulates the link signal and sendsthe data to the master processor board. The masterprocessor compares the received data and selects thesignals with the fewest errors to send to the CDScomputer. Although this mode is normally used withthree HF frequencies and one UHF frequency, there isno set limitation of the radio configuration.

On-line and Off-1ine System Test Options

The data terminal provides several options forboth on-line and off-line testing. These include thefollowing: radio echo test, loopback tests 1, 2, 3, and4, and DTS fault isolation tests. The radio echo test,loopback test 1, and loopback test 4 are on-line tests,while loopback test 2, loopback test 3, and the DTSfault isolation tests are off-line tests.

RADIO ECHO TEST. —When this option isselected, the data terminal is placed in full-duplexmode. This option is selected when a single stationPOFA is run with the radio and checks the operationof the computer interface, the crypto device, the dataterminal, and the radio.

LOOPBACK TEST 1. —Loopback test 1 isselected when running a single station POFA withoutthe radio. When you select this test option, the audiolines are internally disconnected from the radio andthe audio outputs are connected to the audio inputs.Full-duplex operation is also enabled. This testchecks the operation of the computer interface, thecrypto device, and the data terminal.

LOOPBACK TEST 2. —Loopback test 2configures the data terminal for an off-line self-test.The audio lines are disconnected from the radio andthe audio output lines are internally jumpered to theaudio input lines. A test message is internallygenerated and sent through the audio circuits. Thereceiver output is monitored for data errors, parityerrors, control code errors, and preamble recognition.Any errors detected will cause the LOOPBACK FAILindicator to be displayed.

LOOPBACK TEST 3. —Loopback test 3 is adata terminal to radio test. Normal audio connectionsare maintained, while the computer interface isdisabled. A test message is internally generated andrepeatedly sent through the radio. As with loopbacktest 2, the receiver output is monitored for data errors,parity errors. control code errors, and preamblerecognition. Any errors detected will cause theLOOPBACK FAIL indicator to be displayed.

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LOOPBACK TEST 4. —Loopback test 4 is usedto check the operation of the computer interface, thecrypto device, and the data terminal interfacecircuitry. When this test is selected, the audio circuitsare disabled and the data from the computer is sent tothe memory in the data terminal. Upon receipt of theend of transmit signal, the data in memory is sent backto the computer for evaluation.

DTS FAULT ISOLATION TESTS. —The DTSfault isolation tests are built-in tests (BIT) designed totest and isolate a fault to a particular circuit board.

REMOTE CONTROL UNIT

The C-12428/USQ-125 remote control unit (CU)enables the operator to control the data terminal froma remote location. The control unit, used with thedata terminal, forms the data terminal set (DTS). Thecontrol unit is used by the operator to enter operatingparameters, start and stop link operations, and changelink modes. One model, shown in figure 7-4, consistsof a 486DX2/66 MHz AT compatible personalcomputer in a rugged chassis for shipboard operation.The keyboard/trackball unit is in a special detachableenclosure that also serves as a front cover for the CU.A 386 or better personal computer maybe substitutedfor the control unit when loaded with the propersoftware and connected to the data terminal.

Figure 7-4.—The C-12428/USQ-125 Control Unit.

THE JOINT TACTICAL INFORMATIONDISTRIBUTION SYSTEM (LINK-16)

The Joint Tactical Information DistributionSystem (Link-16) is a new tactical data link that wasintroduced to the fleet in 1994. Link-16 has beenreferred to by several names and acronyms. TheTactical Digital Information Link (TADIL) is a termused by the U. S. Joint Services. The TADILdesignation for Link-16 is TADIL J. The JointTactical Information Distribution System (JTIDS)refers to the communications component of Link-16.The communications component includes the terminalsoftware, hardware, RF equipments, and thewaveforms they generate. The NATO terms forJTIDS is the Multifunctional Information DistributionSystem (MIDS). For our purposes, we will use theterm Link-16 when referring to this system.

FEATURES OF LINK-16

Link-16 allows for the exchange of real-timetactical information between units of the Navy, theJoint Services, and the members of NATO. Althoughsome of the functions are identical to the functions ofLink-11 and Link-4A, Link-16 also provides dataexchange elements that the other link systems lack.These include the following:

Nodelessness

Jam resistance

Flexibility of communication operations

Separate transmission and data securityfeatures

Increased numbers of participants

Increased data capacity

Network navigation features

Secure voice capabilities

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Transmission Protocols

Since Link-16 exchanges much of the same datathat is used in both Link-11 and Link-4A, a briefcomparison of the architectures, the capacities, andthe data rates of the three systems is useful.

During normal operation, Link-11 operates usingthe protocols of the Roll Call mode. In this mode,each participating unit is polled by the NCS totransmit data. On completion of data transmission,the unit returns to the receive mode and the next unitis polled until all units have been polled. This cycleis continuously repeated. Link-11 messages are calledM series messages.

Link-4A uses the time-division multiplexingprinciple with a command-and-response protocol toenable the operator to control multiple aircraftindependently on the same frequency. Link-4Amessages sent to the controlled aircraft are referred toas V series messages and messages received from thecontrolled aircraft are called R series messages.

Link- 16 uses the Time-Division Multiple Access(TDMA) principle of data communications. Usingthis architecture with time interlacing provides thesystem with multiple and apparently simultaneouscommunications nets. Instead of assigning each unita PU number, Link-16 assigns each unit a JTIDSUnit number, or JU. The JU identifies the units anddetermines a preassigned set of time slots thatdesignate when the unit transmits and receives data.Each time slot is 1/128 of a second, or 7.8125milliseconds, in duration.

When a JU transmits data, the frequency that thedata is t ransmit ted on is changed every 13microseconds (µsec), according to a predeterminedpseudo-random pattern. Link-16 uses 51 differentfrequencies for data exchange. This frequencyhopping adds to the security and integrity of thesystem by making it nearly impossible to jam.

Link-16 Nets

Link-16 has the capability to handle multiple nets.A Link-16 net is a group of participants sharing

mutually beneficial tact ical information. Forexample, using the Link-11 system, a net is formed bya group of participants. These participants operate onthe same frequency. A separate net is formed whenanother group of participants operates on a differentfrequency. The second net would be used byparticipants involved in a fleet exercise that wouldn’twant the exercise data to interfere with the normaltactical net. The controlling station and aircraft usingLink-4A is also a net.

Link-16 has the ability to form multiple nets. TheLink-16 system has 128 numbers used to designateparticular nets (00-127). Net number 127 is reservedto indicate a stacked net. A stacked net is formed bysetting up the time slots so that they have the sameset, initial slot number, and recurrence rate. Whenthe system is initialized, the use of net number 127indicates a stacked net is to be used and the operatorcan then specify locally which net to use foroperations. Figure 7-5 illustrates the concept of astacked net used for air control. Net 1 is a group ofaircraft controlled by the ship, while Net 3 is a groupof aircraft controlled by an E-2. If the E-2 requiresadditional aircraft, the ship can direct the aircraftunder i ts control to the E-2. As the aircraftapproaches the E-2, the pilot can switch to Net 3 andimmediately become an active participant in the newnet. Even though the operator has several netsavailable to monitor or use, a single terminal cantransmit or receive on only one of them for each timeslot. Stacked nets are possible because the frequency-hopping pattern is different for each net. Examples ofstacked nets are voice nets and control nets.

Figure 7-5.—Stacked nets using Link-16.

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Link-16 Data Exchange

Link-16 transmits data serially using 70 bit datawords. During the transmit time slot, either three, six,or 12 data words can be transmitted. The number ofwords transmitted depends on whether the standard,packed-2, or packed-4 data packing structure is used.The number of words that composes a Link-16message is variable but is normally 1, 2, or 3 words.There are three types of messages: fixed format, freetext, and variable format. The fixed format messagesare called J-series messages and are used to exchangetactical information. Free text messages are used forvoice communications, while the variable formatmessages are user defined in length and content.Variable format messages are not used by the Navy.

JTIDS Architecture

There a re severa l f ea tu res o f the JTIDSarchitecture that have resulted in improvedcommunications of the Link-16 system. Thesefeatures include the following:

Nodelessness

Security

Network participation groups

NODELESSNESS. —A node is a unit required tomaintain communications of a data link. In Link-11,the NCS is a node. If the NCS goes down, the entirenet is inoperative. Link-16 does not need a dedicatedstation. When the Link-16 net is established, a singleJU transmits a Network Time Reference (NTR).The time established by this unit is the networksystem time. All other units in the net use the NTRmessage to synchronize with the network. Once theNTR and the network have been established, thenetwork can continue to operate regardless of theparticipation of any particular unit.

SECURITY. —The security of the Link-16system is vastly improved over that of the Link-11sys tem. In L ink-16 , bo th the da ta and thetransmissions are encrypted. Data is encrypted by a

cryptovariable for message security. The security ofthe data transmission is provided by the use of asecond cryptovariable that controls the transmittedwaveform. Frequency hopping to prevent jamming isone of the features of the security system. Thet ransmiss ion secur i ty a l so p rov ides fo r theintroduction of jitter and a pseudo-random noise to beadded to the waveform. The addition of jitter andnoise, along with the frequency hopping, makes thetransmitted signal extremely difficult to detect andjam.

N E T W O R K P A R T I C I P A T I O NGROUPS. —The time slots of a Link-16 network canbe broken down into separate Network ParticipationGroups (NPGs). An NPG is defined by its functionand determines the types of messages that aretransmitted on it. Some of the NPGs used by theNavy are as follows:

Surveillance

Electronic Warfare

Mission Management

Weapons Coordination

Air Control

Fighter-to-Fighter

Secure Voice

Precise Participant Location and Identification(PPLI) and Status

By dividing the net into NPGs, each JU canparticipate on only the groups that support the missionof the unit. Most Navy Command and Control (C2)units, both ships and aircraft, operate on all thedefined NPGs except the Fighter-to-Fighter NPG.

Link-16 New Capabilities

The increased size of the Link-16 enables thereporting of up to three times as much tacticalinformation as was available under the Link-11

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system. Areas that have been improved under theLink-16 system include the following:

Number of Participants

Track Numbers

Track Quality

Track Identification

Friendly Status

Granularity of Measurement

Relative Navigation

Electronic Warfare

Land Points and Tracks

NUMBER OF PARTICIPANTS. —The numberof units that can participate in a Link-16 net has beenincreased dramatically over that of Link-11. TheJTIDS Unit number, or JU, is a five-digit octalnumber from 00001 to 77777. This allows for amaximum of 32,766 possible JUs. Addresses 00001to 00177 are normally assigned to units that have theneed and capability to participate in both Link-16 andLink-11. When a unit participates in both Link-11and Link-16, it must use the same address on bothlinks. For example, Link-16 JU 00043 is the same asLink-11 PU 043.

TRACK NUMBERS. —Link-l6 replaces the oldfour-digit (octal) Link-11 track numbers with a five-character alphanumeric track number. The tracknumber can be within the range 00001 to 77777(octal) or 0A000 through ZZ777. This allows for amaximum of 524,284 track numbers, compared withthe 4,092 available with Link-11. One reason for theneed for the additional track number is that Link-16cannot operate in the track number pool mode, inwhich a common pool of track numbers is shared byseveral PUs. Every JU must be assigned a uniqueblock of track numbers.

To maintain interoperability with Link-11,Link-16 track numbers 00200 through 07777designate the same track as Link-11 track numbers0200 through 7777.

TRACK QUALITY. —The Track Quality (TQ)value used by Link-16 relates to the accuracy of thereported position of the track. The TQ has a range of0 to 15. To achieve the highest track quality, the trackmust be within 50 feet of the reported position.Link-11 uses the update rate to determine trackquality. Using Link-11, a track that is reported by aPU at every interrogation is usually assigned a TQ of7. Therefore, a Link-11 air track with a TQ of 7 canbe more than 3 nautical miles from its reportedposition.

TRACK IDENTIFICATION. —The Link-16system greatly expands the information that isreported with Track Identification (ID). The new IDreports include fields for platform, activity, specifictype, and nationality of the track. Additionalprovisions have also been added to identify a track as“Neutral,” and the Unknown Assumed Enemy ID ischanged to “Suspect.”

FRIENDLY STATUS. —The Link-16 systemalso provides for more detailed status reports fromfriendly aircraft. The following fields are added toLink-16 friendly status reports: equipment status,ordnance inventory, radar and missile channels, fuelavailable for transfer, gun capability, and station ETAand ETD.

INCREASED GRANULARITY. —Granularityrefers to how precisely an item is reported in the linkmessage. Link-16 has made major improvements inthe granularity of reports concerning track position,air track speed, altitude, and lines of bearing.

LINES AND AREAS. —The Link-16 systemallows the reporting of multi-segment lines and areasof all sizes and descriptions. Link-11, for comparison,only allows reports of areas that are limited in sizeand are circles, ellipses, squares, or rectangles.Link-11 does not have the capability to report lines.

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GEODETIC POSITIONING. —The Link-16messages use the geodetic coordinate system to reportpositions. This system uses latitude, longitude, andaltitude to report positions anywhere in the world.Link-11 uses the Cartesian coordinate system, whichrequires the reporting unit to be within a certain rangewhen reporting positions.

RELATIVE NAVIGATION. —The RelativeNavigation (RELNAV) function of the Link-16system is automatically started by every Link-16participant and is constantly operating. The RELNAVfunction determines the distance between reportingunits by measuring the arrival times of transmissionsand correlating them with the reported position of theunit. This information is required by each terminal inthe network to maintain synchronization. TheRELNAV data can also improve a unit’s positionalaccuracy. Also, if two or more units have accurategeodetic positions, RELNAV can provide all otherunits with accurate geodetic positions.

ELECTRONIC WARFARE. —The Link-16system increases the types and amount of electronicwarfare information that is exchanged between units.

LAND POINTS AND TRACKS. —The Link-16system adds Land as a track category, and allows thereporting of land objects, such as buildings orvehicles.

EQUIPMENT CONFIGURATION

Currently, Link-16 will be installed onboardaircraft carriers, cruises, destroyers, and amphibiousassault ships. Two phases of shipboard installation,designated Model-4 and Model-5, are planned.

Model-4 is being installed on ACDS and AEGISplatforms in conjunction with the installation of theCommand and Control Processor (C2P). Model-4does not implement any of the expanded dataexchange capabilities of Link-16. Instead, it supportsexisting Link-11 and Link-4A with its jam-resistant,increased capacity waveform. Platforms with theModel-4 Link-16 system will retain their original

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Link-11 and Link-4A systems, and can use thesesystems by placing the C2P in bypass. Model-4 isbeing installed on very few ships, most of which willbe upgraded to Model-5; therefore, our discussion ofLink-16 equipment will concern the Model-5 system.

Link-16 Model-5

The major components of the Link-16 system arethe Tactical Data System (TDS), the C2P, and theJTIDS terminal, as shown in figure 7-6. The TDS andC2P provide the JTIDS terminal with tactical data tobe t r ansmi t t ed . The L ink-16 Mode l -5 fu l lyimplements all the capabilities of Link-16. For thisimplementation to take place, major software changesmust be made to the TDS and C2P programs. Also,the OJ-663 console replaces the current display

Figure 7-6.—The Link-16 Model-5 ACDS system blockdiagram.

Data flow to the Link-16 JTIDS terminal is fromthe ACDS computer, through the C2P computer, tothe Link-16 computer. Link data generated by theACDS computer is now normalized to be independentof any one particular link system. The C2P computerreformats the normalized data into the formatnecessary for transmission over Link-16. The C2Pcomputer can also format the normalized data fortransmission over Link-11 and Link-4A. If necessary,all three link systems can be in operation at the sametime.

The JTIDS Terminal

The JTIDS terminal used in Link-16 is theAN/URC-107(V)7. This is an advanced radio systemthat provides secure, jam-resistant, digital data andvoice communication among a large number of users.This radio system combines the functions performedby the Link-11 crypto device, data terminal set, andradio into one cabinet. Many other capabilities arealso incorporated in the radio. These addedcapabilities include the following:

Precise participant location and identification

Relative navigation

Synchronization

Secure voice

Relay

Built-in test

Shipboard Terminal

Figure 7-7.—The AN/URC-107(V)7 JTIDS data terminal.

7-7. The components of the JTIDS terminal includethe Digital Data Processor Group (DDPG), the

The AN/URC-107(V)7 JDIDS terminal is a singlefive drawer electronics cabinet, as shown in figure

Receiver/Transmitter Group (R/T), the High-Power Amplifier Group (HPAG), and the PowerInterface Unit (PIU). The Secure Data Unit (SDU)

Figure 7-8.—The JTIDS terminal functional block diagram.

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is a separate assembly that is mounted to the DigitalData Processing Group. Figure 7-8 is the functionalblock diagram of the JTIDS terminal.

D I G I T A L D A T A P R O C E S S O RGROUP. —The third drawer of the terminal housesthe digital data processor group. The two majorcomponents are the interface unit (IU) and thedigital data processor (DDP). A battery assembly ismounted to the front of the DDPG drawer. Thisassembly consists of one nickel cadmium (NiCad)battery and two lithium sulphur dioxide cells. TheNiCad battery will provide power to cri t icalcomponents during short power failures. The lithiumsu lphur d iox ide ce l l s supp ly power to thechronometer.

The Interface Unit controls the communicationsbetween the JTIDS terminal and the host computerand provides amount for the Secure Data Unit (SDU).On shipboard systems, the C2P is the host computer.The Subscriber Interface Computer Program(SICP) is a software program that controls thecommunications with the host computer and providesthe data processing necessary to integrate the terminaland the host computer. The IU and SICP also provide

the following functions: analog-to-digital and digital-to-analog conversion of voice signals, feed throughinterface between the DDP and the SDU, and primaryand backup power interface. The IU also provides theinterface for receiving and supplying the TACANblanking pulses. These blanking pulses prevent theTACAN and the JTIDS terminal from transmitting atthe same time.

The Digital Data Processor (DDP) controls thereceiver/transmitter and the high-power amplifiergroups. The DDP performs the processing requiredfor transmitting and receiving Link-16 messages.This processing includes the following:

Data encryption and decryption

Error detection and correction encoding anddecoding

Generation of the frequency-hopping pattern

Selection of the carrier frequency

Measurement of time of arrival data forposition and synchronization calculations

Figure 7-9.—The Digital Data Processing Group functional block diagram.

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Execution of the Built-in Tests (BIT) for fault

isolation

Generation of alerts

The Network Interface Computer Program(NICP) is the software that runs in the DDP and isresponsible for the communications with the JTIDSR F n e t w o r k . T h e N I C P c o n t r o l s m e s s a g etransmission and reception processing, coarse and fineterminal synchronizat ion, relat ive navigat ionprocessing, and terminal and network monitoring.

Figure 7-9 is the block diagram for the DDPG.The global memory in the DDP is shared by all theprocessors in the terminal. Communications betweenthe processors is over an internal bus called the plaintext bus. All transactions on the plain text bus areeither read or write commands to the global memoryor port-to-port transfers. When the SICP, running inthe IU, needs to communicate with the NICP, it doesso by using the shared global memory in the DDP. Aport-to-port transfer is a transfer of data betweenports, such as when communicating with the hostexternal timer (see fig. 7-9).

SECURE DATA UNIT. —The SDU is aremovable assembly that is mounted to the IU. Itstores the cryptovariables that are loaded duringinitialization. The SDU provides for both messagesecurity and transmission security. Message securityis provided by the encryption of the data, whiletransmission security is provided by the pseudo-random f requency-hopp ing pa t t e rn and theintroduction of a pseudo-random pattern of noise andjitter on the RF signal.

RECEIVER/TRANSMITTER GROUP. —TheR/T is in the top drawer of the equipment cabinet andprocesses the radio frequency signals. The R/T alsogenerates a 75-MHz intermediate frequency signalused for internal communication between the R/T andDDPG. When a Link-16 message is received, the R/Tconverts the RF to the intermediate frequency andsends it to the DDPG for processing. When theterminal transmits a Link-16 message, the R/Treceives a Continuous Phase-Shift Modulation (CPS)

IF signal from the DDPG. The R/T then converts it toa 200-watt RF signal that is sent to the high-poweramplifier group.

HIGH-POWER AMPLIFIER GROUP. —TheHPAG is in the second drawer of the equipmentcabinet and consists of a high-power amplifier and theantenna interface unit (AIU). The signal from the R/Tgroup is received by the HPAG and amplified from200 to 1,000 watts. The HPAG can also operate in alow-power mode, in which case the output signal isabout 200 watts. The AIU provides the interfacebetween the output of the HPAG and the antenna.

POWER INTERFACE UNIT. —There are twoPower Interface Units (PIUs) in the equipmentcabinet. The fourth drawer is the HPAG PIU and thebottom drawer is the PIU for the R/T and DDG. Thetwo PIUs are identical. The three-phase, 115-VAC,60-Hz input power is converted to two outputs: three-phase, 115-VAC, 400-Hz, and one-phase, 115-VACat 400 Hz.

THE COMMAND AND CONTROLPROCESSOR

The Command and Control Processor (C2P) is amessage distribution system designed to control andmanage the interfaces between the three tactical datalinks (Link-4A, Link-11, and Link-16), the operator,and the hardware.

PURPOSE OF THE C2P

The C2P controls and manages the interfacesbetween the various data links on major surface andaircraft Command and Control (C2) platforms. Thesurface platforms that will have the initial installationsof the C2P system are aircraft carriers (CV, CVN) andAEGIS cruisers (CG), followed by installation onamphibious assault ships (LHA, LHD), and AEGISdestroyers (DDG). There are two configurations ofthe C2P, one tailored for ships with the AdvancedCombat Di rec t ion Sys tem (ACDS) Block 0c o n f i g u r a t i o n a n d o n e f o r A C D S B l o c k 1configurations. On AEGIS ships, AEGIS Model 4 issimilar to ACDS Block 0, and AEGIS Model 5 issimilar to ACDS Block 1. The C2P system installed

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Figure 7-10.—The C2P system block diagram for ACDS Block 0 platforms.

on an ACDS Block 0 platform is very similar to thesystem that is installed on an AEGIS Model 4platform. Figure 7-10 illustrates the system blockdiagram of the C2P for ACDS Block 0 platforms.

Link messages generated in the ACDS computerare sent to the C2P computer where they are formattedfor transmission on the proper link (Link-4A, Link-11,or Link-16). Depending on the mode of operation andoperator entered parameters, some messages may besent over two or more data links. For example, it isno t uncommon fo r L ink-11 messages to betransmitted over Link-11 and Link-16. The C2Pcomputer stores the data in a central database, calledthe normalized data base, and then formats the data inthe proper message format for the link system(s) beingused.

Messages received by the various data links areprocessed for errors by the C2P computer and sent tothe proper destination. Received messages can alsobe reformatted for retransmission on a different link.A Link-11 or Link-4A message received by a C2Pplatform can be reformatted into a Link-16 message

and retransmitted on Link-16.

SYSTEM CONFIGURATION

The hardware block diagram of the equipmentused in the C2P system is shown in figure 7-11. TheAN/UYK-43(V) is a general-purpose, large scale,tactical computer used to store and execute the C2Psoftware. The C2P configuration of the AN/UYK-43consists of the following major modules:

Two central processor units

Two input/output controllers and adapters

Six expanded time volatile memory units

One embedded memory subsystem (EMS)with two embedded mass memory storagedevices (EMMSD)

A major change in the configuration of theAN/UYK-43A(V) is the EMS and its associatedEMMSDs. The EMS consists of two 383 megabyte

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Figure 7-11.—The C2P system hardware configuration.

in the computer, the software accesses them as if theywere external disk drives.

The AN/USQ-69(V) data terminal set is used toprovide the man-machine interface (MMI). It isinstalled next to the Track Supervisor in CIC.

Several equipments are shared between the ACDSsystem and the C2P system. These include themagnetic tape unit, a teleprinter, and a secondAN/USQ-69(V) data terminal set. The magnetic tapeunit is used for initial program loading (to EMS), dataextraction, and reading and writing JTIDS informationto and from tape. It is also a backup load device whenthe EMS is down. The teleprinter provides hard copyprintouts of C2P system status, error codes, and datadumps. The second AN/USQ-69(V) is used as abackup.

Shared equipments are switched to the desiredsystems through the Combat Systems Switchboard.The switchboard also provides switches to connectLink-4A and Link-11 directly to the CDS computer,bypassing the C2P system.

hard drives installed in the AN/UYK-43(V) cabinet.Even though these disk drives are internally installed

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CHAPTER 8

LOCAL-AREA NETWORKS

INTRODUCTION

A local-area network (LAN) is a communications system designed to transmit and receive digitalinformation between computers. A LAN consists of nodes that are interconnected by links. Nodesare the hardware connected to the network, such as personal or microcomputers, printers, largecapacity hard drives, and so on. Links are the communications media, such as twisted-pair wire,coaxial, or fiber-optic cables that connect the nodes In most applications, the LAN interconnectsa relatively small number of personal computers (PCs), data storage devices, printers, and otherperipherals. These nodes and links usually cover a relatively small geographical area, such as anoffice or a department. Through common usage, the term local-area network can also refer to muchlarger systems, such as the SNAP III system on a ship, which could have literally hundreds ofterminals and miles of cables. For our purposes, we will be using a small system in our discussionof LANs.

Any device connected to the network can send and receive data on the network. A majority ofdata exchanged over a network is text and graphics, which is assembled as structured data that canbe manipulated by computers. Unstructured data, such as pictures and facsimile messages, can bestored and retrieved efficiently, but cannot be manipulated easily by the computer.

After completing this chapter, you should be able to:

Describe the major components of a LAN.

State the types of cable used in a LAN.

State the function of the network interface card.

Describe the function of the various network servers required by a LAN.

Describe the function of the central mass storage area of a LAN.

Describe the Open System Interconnection (OSI) Reference Model used in the designand implementation of a LAN.

Describe the advantages and disadvantages of the different LAN topologies.

Describe the hardware systems used in LANs.

Describe the function of the software operating system of a LAN.

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LOCAL-AREA NETWORK HARDWARE

The basic hardware components of a LAN arecables, network interface cards, network servers,peripherals, and workstations. These components arecovered in the material that follows.

CABLES

Several types of cables can be used in LANapplications. The selection of the type of cabledepends on several factors, such as maximum lengthof a single cable run, security requirements, and thecapacity and speed of the system.

Twisted-Pair Cable

The twisted-pair cable is easy to install and costslittle on a per-foot basis. In some cases, existingtelephone cable may be used. Its disadvantagesinclude limitations in capacity and speed. It is alsosusceptible to electrical interference unless it isshielded.

Shielded Twisted-Pair Cable

The shielded twisted-pair cable is encased in anRFI shield. The stranded wire used as a conductor ismanufactured with greater precision and is capable ofgreater data transmission rates and longer cable runs.

Coaxial Cable

Coaxial cable networks have gained in popularitybecause of their use in cable television. Thequantities of cable and connectors produced for cabletelevision have greatly reduced the prices of thesecomponents for network users. Coaxial cable comesin various thicknesses and is designated by a number:RG-11, RG-58, RG-59, RG-62, and so forth. You canuse either baseband or broadband transmissionmethods with coaxial cable.

Baseband coaxial systems transmit digital signalsunchanged over a single channel and have severaladvantages. They are inexpensive, easy to install, andhave low maintenance. They also allow very high

data transmission rates. One disadvantage is that theyare limited to transmitting digital signals only.

In contrast, broadband coaxial systems requirethe digital signal to be converted to an analog signalbefore transmission and then back to digital bymodem at the receiving device. Broadband systemssupport data, voice, and video signals that may betransmit ted simultaneously. Disadvantages ofbroadband systems are their higher installation costsand complex maintenance.

Fiber-Optic Cable

Fiber-optic cable is the best choice if a securenetwork is needed. Because the cable transmits light,the transmissions are immune to interference causedby electrical or electronic devices. Also, if yournetwork will run through an area of heavy industrialactivity or a work place with strong radio frequencyinterference, fiber-optic cable is the most appropriatechoice. Other advantages of the fiber-optic cable arethat it lasts longer than other types of cable and cancarry many more channels. Its disadvantages includeits high price, poor connectivity, and low flexibility.

NETWORK INTERFACE CARD

To attach personal computers to the LAN, youmust connect a network interface card (NIC) to eachPC and attach the network cable to the NIC. Eachindividual workstation must have a network interfacecard. The NIC is nothing more than a circuit boardthat normally plugs directly into one of the expansionslots inside a PC. Sometimes, the NIC comes as aseparate unit. In this case, you would plug it into theback of the PC. Most NICs have their own built-inmicroprocessor(s) designed to take care of networkcommunications. This rel ieves the PC’s mainprocessor of this responsibility. The type of cableused on the network is determined by the type of LANto be installed.

NETWORK SERVERS

Your understanding the concept of a server i simportant to understanding how LANs work. Aserver is a combination of hardware and software that

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is used to manage the shared resources of the network.The hardware may be a PC or a computer designedspecifically to act as a server. A network server isable to control network traffic as well as the sharingof other resources, such as application programs, diskspace, data files, and printers. In either case, thecomputer normally has a hard disk and the softwareneeded to run the network system. There are severaldifferent types of servers, and each has a particularfunction. In newer systems, some separate serverfunctions are combined into a central file server. Theservers we will look at are the disk server, the fileserver, and the print server.

Disk Server

The disk server was the first of the networkoperating systems. In the early days of PC networks,very few computers were equipped with a hard disk.When the hard disk became affordable, manufacturerswere asked to develop a system to allow several usersto share a single hard drive. The earliest disk serverswere mult iplexers that polled each connectedcomputer for requests to write a file on the hard driveor to retrieve a file from the disk. The multiplexerthen responded accordingly. A major problem withthis process was that it did not allow for any type ofsecurity, data organization, or disk management.

As LAN technology evolved, the development ofthe disk server software in the early 1980s addressedsome of these issues. The disk server is a softwareroutine that was installed on each computer in thenetwork. The disk server software allowed each PCto access the shared hard drive as if it were a localdrive. In other words, the computer thought the drivewas installed in the computer, but in reality, the drivewas remotely located on the network.

The d i sk se rve r a l so p rov ided fo r someinformation sharing. One purpose of a network is toallow multiple users access to the same information.One problem encountered with early disk serversoccurred when two or more users updated the samefile at the same time. When the file was saved byboth users, the updates of one of the users was lost.

A method of preventing this information loss isfile locking. File locking means that when one useraccesses a file, all the other users are prevented fromaccessing that file until the first user is finished withit. As you can see, this method severely limits thenumber of users able to access the information.

Another method used to prevent data loss is recordlocking. In a data-base environment, many userscould access the same data file, but when a record wasbeing modified by one user, the other users werelocked out of the record being modified. A data filecan be updated by several users without threateningthe integrity of the data by using this technique.

Although the disk server was used in most LANsdeveloped before 1985, a major problem still existedin maintaining data integrity. The two methodscovered in the previous paragraphs provided for datamanagement, but not for reliable disk management.A disk drive stores information on the next availableblock on the disk. When the disk server was used, itwas not uncommon for two users to try to write datato the same block at the same time. When thishappened, the second user would overwrite the datajust written by the first user, causing a loss of data.The development of the file server in 1983 solved allof the problems encountered with the disk server.

File Server

Currently, all local-area networks require sometype of file server. In most cases, the file server is adedicated PC or minicomputer. The file serverperforms the processing of the network controlsoftware and the central processing and storage pointof the application software and data files of thenetwork. The file server has a hard disk with a verylarge storage capacity.

The file server manages the hard disk and ensuresthat multiple requests for the same file do not conflictwith each other. In the disk server environment, eachPC workstation manages its I/O with the disk throughlow-level sector calls. In the file server environment,each workstation communicates with the central diskthrough the use of high-level calls to the file server.A high-level call can be a request to open a particularfile or to store a file, while a low-level call maybe to

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write this file to sector xyz on the disk. The file serverconverts the high-level calls from the users to low-level disk commands, thus providing effective diskmanagement. The file server maintains the list ofprivileges and authorizations for each user. Thisprotects the data files from unauthorized access andprotects the data. An example of this is that one usermay be authorized total access to a data-base file toupdate the file, while another user may be authorizedread-only access to the information. Still a third usermay be denied access to the file altogether.

A network file server is a special-purpose unit thatcan reside in either a dedicated computer, or one ofthe workstations (a PC) that has a hard diskcontaining the software of the network. When thenetwork server is used solely for serving the networkand is NOT used as a workstation, it is referred to asa dedicated server. If the server can also be used asa workstation, it is referred to as a nondedicatedserver.

Some networks do NOT have a single dedicatedfile server. Instead, they use a distributed approachin which any of the nondedicated servers may makeavailable files that reside on their hard disks. Underthese circumstances, any workstation on the networkcan use or copy these files. Moving files back andforth on such a network establishes a temporaryrelationship, you might say, between the two PCsinvolved. One PC acts as the server, and the other PCacts as the receiving workstation.

Print Server

The print server is a software routine that allowsall the workstations on the LAN to use a singleprinter. When the laser printer was introduced to themarket, the extremely high-quality print and multiplefonts made it desirous for all correspondence.Unfortunately, the cost of a laser printer oftenexceeded that of an individual workstation and madeit impractical for each workstation to have a dedicatedprinter. The print server solved that problem byaccepting requests for print jobs from the networkusers and directing them to the printer. The printserver makes sure one job is completed before a newjob is started. Print server routines are included in

almost all network operating systems on the markettoday.

WORKSTATIONS

Workstations is another name for the PCs used ona network. The PCs can be of the same brand, such asZenith, or they can be a combination of differentbrands, such as IBM, Zenith, Compaq, along withother PC compatible computers (clones). Each PCcan be configured differently. Some might have theirown hard disk drives; others might have expandedmemory. Still others might NOT even have diskettedrives or printer ports of their own. Instead, these lessexpensive workstations use the storage and printingresources available through the network. Even thougha PC may be part of a LAN system, you can use itindependently as a stand-alone PC at any time or youcan use it as part of the LAN.

THE OPEN SYSTEM INTERCONNECTION(OSI) REFERENCE MODEL

Over the past few years, a number of networkstandards or protocols (rules to live by) have beendeveloped by the International Standards Organization(ISO) to provide some level of uniformity amongcomputer manufacturers and network vendors. ISO isone of several governing organizations in this fieldthat has developed such protocols. ISO has defined afive level, seven-layer architecture. These seven layersof standards, shown in figure 8-1 define a generalizedarchitecture called the Reference Model of OpenSystems Interconnection. It is also known as theOSI reference model or OSI model. The primarypurpose of the OSI model is to provide a basis forcoordinating the development of standards that relateto the flexible interconnection of incompatiblesystems using data communications facilities.

The OSI model does NOT define anyone vendor’sparticular network software as such, nor does it definedetailed standards for any given software. It simplydefines the broad categories of functions that each ofthe seven layers should perform. The OSI model caninclude different sets of standards at each layer thatare appropriate for given situations. For example, ina very simple data communications system, one that

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Figure 8-1.—The OSI model showing the seven layers.

uses a simple point-to-point link, the software at thehigher level layers (say 5, 6, and 7) might be verysimple or possibly nonexistent. However, in a verycomplex data communications system, all sevensoftware layers may be implemented. Although thereis no requirement for any hardware or software vendorto adhere to the principles set forth in the OSI model,there is a worldwide trend in the computer industrytoward acceptance and conformance to thesestandards.

Ideally, if the hardware, network software,application software, and cabling were all supplied bythe same manufacturer, there would be relatively fewproblems for users to contend with when designingand implementing a network. Everything would worktogether rather smoothly. However, a computermanufacturer’s architecture can make it difficult tointerconnect hardware offered by other competingmanufacturers or vendors. The protocols used bycommunications devices are also highly complex andare often completely different from one manufacturerto another. Then there is the network software.Usually, the network software from one LAN vendorwill not work with that of a competitor, neither willthe application programs. Even the cabling must beselected for a specific local-area network.

HARDWARE LEVEL

and the data-link layer. These are concerned primarilywith the actual hardware used in a network.

Physical Layer

The physical layer is concerned with thetransmission of the unstructured raw bit stream overa physical medium. It describes the electrical,mechanical, and functional interfaces to the carrier.The physical layer carries the signals for all the higherlayers as follows:

Voltages and pulse encoding of bits

M e d i a a n d m e d i a i n t e r f a c e ( c a b l e s ,connectors, NIC, and so on)

Line discipline (full- or half-duplex)

Pin assignments

Data-Link Layer

The da ta - l ink l aye r p rov ides e r ro r - f reetransmission of information over the physicalmedium. This allows the next higher layer to assumevirtually error-free transmission over the link. Thedata-link layer is responsible forgetting data packagedand onto the network cable. It manages the flow ofthe data bit stream into and out of each network nodeas follows:

Creates and recognizes frame boundaries

Checks received messages for integrity

Manages channel access and flow control

Ensures correct sequence of transmitted data

The data-link layer detects and, when possible,corrects errors that occur in the physical layer withoutusing the functions of the upper layers. It alsoprovides flow-control techniques to ensure link-buffercapacity is not exceeded.

The hardware level contains the first two layers ofthe OSI reference model. They are the physical layer

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TRANSPORT LEVEL

The next three layers of the OSI reference modelmake up the transport level, also known as the subnet.The transport level defines the software protocolsnecessary to exchange data on the network. The threelayers of the transport level are the network layer, thetransport layer, and the session layer.

Network Layer

The network layer decides which physicalpathway the data should take based on networkconditions, priorities of service, and other factors.Software on the network interface card must build thedata packet, so the network layer can recognize androute the data to the correct destination address. Itrelieves the upper layers of the need to know anythingabou t the da ta t r ansmiss ion and swi t ch ingtechnologies used to connect the systems. It isresponsible for establishing, maintaining, andterminating connections across the interveningcommunications facility as follows:

Addresses messages

Sets up the path between communicatingnodes on possibly different networks

Routes messages among networks

Is concerned with the sequence delivery ofdata packets

Controls congestion if too many packets areon the network

Translates logical addresses or names intophysical addresses

Has accounting functions to count packets orbi ts sent by users to produce bi l l inginformation

Transport Layer

duplications. It relieves higher layer protocols fromany concern with the transportation of data betweenthem as follows:

Message segmentation. Accepts data from thesession layer, splits it up into smaller units,and passes the units down to the network layer

E s t a b l i s h e s a n d d e l e t e s h o s t - t o - h o s tconnections across the network

Multiplexes several message streams onto onechannel and keeps track of which messagebelongs to which connection

Provides reliable end-to-end delivery withacknowledgment

Provides end-to-end flow control and windowmanagement

Session Layer

The session layer allows users on differentmachines to establish sessions between one another.It performs the functions that enable two or moreapplications to communicate across the network,performing security, name recognition, logging,administration, and other similar functions. Unlikethe network layer, this layer is dealing with theprograms in each machine to establish conversationsbetween them as follows:

Allows two applicat ions processes ondifferent machines to establish, use, andterminate a connection (or session)

Performs synchronization between end-usertasks by placing checkpoints in the datastream so that if the network fails, only thedata after the last checkpoint has to beretransmitted

Provides dialogue control (who speaks, when,how long, and so on)

The transport layer makes sure data units aredelivered error-free, in sequence, without losses or

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PRESENTATION LEVEL/LAYER

The presentation level consists of the presentationlayer. The presentation layer formats data to bepresented to the application layer. It can be viewed asthe translator for the network. This layer provides acommon representation for data which can be usedbetween the application processes. The presentationlayer relieves the applications from being concernedwi th da ta r ep resen ta t ion , p rov id ing syn taxindependence as follows:

Encodes data in a standard way (integers,floating point, ASCII, and so on)

Provides data compression to reduce thenumber of bits that have to be transmitted

Provides data encryption for privacy andauthentication

APPLICATION LEVEL/LAYER

The final level is the application level, whichconsists of the application layer. The application layerserves as the window for the application process toaccess the OSI environment. This layer represents theservices that directly support users and applicationtasks. It contains a variety of commonly neededprotocols for the following items:

Network virtual terminals

File transfers

Remote file access

Electronic mail

Network management

USING THE OSI MODEL

A communications system that does not use alayered architecture can be designed. A specificallydesigned communications system is faster, moreefficient, requires less software code, and eliminatesredundant functions and activities. Why, then, is the

OSI reference model considered the standard indesigning networks and writing software? It isconsidered the standard primarily because the use ofa layered architecture, such as the OSI referencemodel, provides the network with flexibility andmigration.

The greatest advantage of your using layerarchitecture in a network is hardware independence.As advances in technology continue, it is notnecessary to scrap a network completely because onecomponent has been superseded. For example, if youhave a network and need to upgrade the cable to atype that can handle increased data at a faster rate, thelayered architecture of the OSI model will allow youto make this replacement to the physical layer withoutchanging the other layers.

LAN TOPOLOGIES

The physical arrangement of the components of aLAN is called its configuration or topology. The threemajor types of configurations, or topologies, of a LANare the linear bus, the star, and the ring. You canalso create hybrid topologies by combining features ofthese configurations. For example, several busnetworks can be joined together to form a ring ofbuses.

Each topology requires the components of a LANto be connected in a different arrangement. Thesecomponents are also referred to as nodes. A node isany point on a network where data can be sent(transmitted) or received—a workstation, a server,and so on.

LINEAR BUS NETWORK

The linear bus topology is like a data highway.That is, all components or nodes are connected to thesame cable, and the far ends of this cable never meet,as shown in figure 8-2. Linear bus LANs are bestsuited to applications involving relatively low usageof the bus coupled with the need to pass relativelyshort messages from one node to another. In manysuch networks, the workstations check whether amessage is coming down the cable before sendingtheir messages. Since all nodes share the bus, all

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messages must pass through the other workstations onthe way to their destinations. Each node checks theaddress attached to the message to see if it matches itsown address. Bus topologies allow individual nodesto be out of service or to be moved to new locationswithout disrupting service to the remaining nodes.

Because of the way linear bus cabling is laid out,this type of network is simple. The bus topology isvery reliable, because if any node on the bus networkfails, the bus itself is NOT affected, and the remainingnodes can continue to operate without interruption.Many of the low cost LANs use a bus topology andtwisted-pair wire cabling.

Figure 8-2.—A bus network topology.

A disadvantage of the bus topology is thatgenerally there must be a minimum distance betweenworkstations to avoid signal interference. Anotherdisadvantage is that the nodes must conpete with eacho the r fo r the use o f the bus . S imul t aneoustransmissions by more than one node are N O Tpermitted. This problem, however, can be solved byusing one of several types of systems designed tocontrol access to the bus. They are collisiondetection, collision avoidance, and token passing,which we will cover shortly. Also, there is no easyway for the network administrator to run diagnosticson the entire network. The bus network can be easilycompromised by an unauthorized user, since allmessages are sent along a common data bus. For thisreason, it is difficult to maintain network security.

Figure 8-3.—A star network topology.

STAR NETWORK

In a star network, each component is connecteddirectly to the central computer or network server, asshown in figure 8-3. Only one cable is required fromthe central computer to each PC’s network interfacecard to tie that workstation to the LAN. The star isone of the earliest types of network topologies. It usesthe same approach to sending and receiving messagesas our phone system. Just as a telephone call fromone person to another is handled by a centralswitching station, all messages must go through thecentral computer or network server that controls theflow of data. New workstations can be easily addedto the network without interrupting other nodes. Thisis one of the advantages of the star topology.

Another advantage of star topology is that thenetwork administrator can give selected nodes ahigher priority status than others. The centralcomputer looks for signals from these higher priorityworkstations before recognizing other nodes. The startopology also permits centralized diagnostics(troubleshooting) of all functions. It can do thisbecause all messages must first go through the central

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computer. This can prove invaluable in making surethat network security has not been breached.

The main disadvantage of the star topology is itsreliance on the central computer for performingalmost all the functions of the network. When thecentral computer fails, all nodes also stop functioning,resulting in failure of the entire network.

DISTRIBUTED STAR

The distributed star, or tree, topology is shown infigure 8-4. It provides many of the advantages ofboth bus and star topologies. It connects workstationsto a central point called a hub. This hub can supportseveral workstations or hubs which, in turn, cansuppor t o the r works ta t ions . D i s t r ibu ted s t a rtopologies can be easily adapted to the physicalarrangement of the facility site. If the site has a highconcentration of workstations in a given area, thesystem can be configured to more closely resemble astar topology. If the workstat ions are widelydispersed, the system can use inexpensive hubs withlong runs of shared cable between hubs, similar to thebus topology.

RING NETWORK

In a ring network, all the components or nodes areconnected to the main cable, and the cable forms aring, as shown in figure 8-5. This topology allows anode to send a message to another node on the ring.

Figure 8-5.—A ring network topology.

However, the message must be transmitted througheach node until it reaches its destination. Messagesproceed from node to node in one direction only.Should a node fail on the network, data can no longerbe passed around the ring unless the failed node iseither physically or electronically bypassed. Usingbypass software, the network can withstand the failureof a workstation, by bypassing it, and continue tomaintain the integrity of the network. One of themajor issues in a ring topology is the need for makingsure all workstations have equal access to thenetwork.

One of the major disadvantages of ring topologiesis the extreme difficultly of adding new workstationswhile the network is in operation. Normally theentire network has to be brought down while a newnode is added and cabling reattached. However, thisparticular problem can be overcome by the installation

Figure 8-4.—A distributed star (tree) network topology.

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of additional connectors when the network is initiallyset up. These connectors enable you to add or remove

nodes while the network remains intact and inoperation.

ACCESS METHODS

Another decision the designer makes is that ofwhich access method to use. Access methods are thearrangements used to make sure each workstation hasfair and equal access to the network. The accessmethod used is governed primarily by the topologyand the protocol of the network. The principal accessmethods are contention and token passing.

Contention

The contention method features Carrier SenseMultiple Access (CSMA) and Carrier Sense MultipleAccess with Collision Detection (CSMA/CD). TheCSMA/CD method is shown in figure 8-6. Access forboth is on a first-come, first-served basis. The CSMAaccess scheme is very similar to that of a citizensband (CB) radio. Stations with data to send listen tothe channel and wait until it is clear to transmit. WithCSMA/CD, when two or more workstations transmitsimultaneously, their messages will collide. As soonas a workstation detects a collision, it ceasestransmission, monitors the network until it hears noother traffic, and then retransmits. Most contentionnetworks assign a unique retry algorithm to vary thewait-and-retry period. This algorithm reduces thelikelihood that after a collision, two workstations willtransmit retries simultaneously.

Token Passing

Token passing is an orderly access method and isshown in figure 8-7. Each workstation passes on theopportunity to transmit to its closest neighbor until astation is found with a message to send. Thispermission to transmit is called a token. When aworkstation with data to send is handed a token, partof the token is changed, indicating it is carrying amessage, and then data is transmitted with the token.The token is then passed around the network, andevery station checks whether the message is intendedfor it. The receiving station copies the message from

Figure 8-6.—A bus network using the CSMA/CD accessmethod.

the token, but then passes the unchanged token alongthe network. When the transmitting station receivesthe same token, it knows the message has been passedaround the network. The transmitting station erasesthe message and puts the empty token back intoc i rcu la t ion on the ne twork . The amount o finformation that may be transmitted during possessionof the token is limited so that all workstations canshare the cable equally.

PROTOCOLS

Network protocols are an important componentbecause they define how networks establish

8-10

communica t ions be tween e lement , exchangeinformation, and terminate communicat ions.Protocols have two major operational functions. Theyestablish the circuit for transmission (handshaking)and for the transmission itself. Transmission isconducted subject to the line discipline. The linediscipline is the sequence of operations that actuallytransmits and receives the data, handles theerror-control procedures, handles the sequencing ofmessage blocks, and provides for validation forinformation received correctly.

Two representative protocols, which control lined i s c i p l i n e , a r e t h e B i n a r y S y n c h r o n o u scommunica t ions P ro toco l (B i sync) and theSynchronous Data Link Control (SDLC).

Bisync

Bisync is a half-duplex protocol that transmitsstrings of characters at lower speeds over dial-upcircuits. The information movement is in onedirection at a time, with each data transfer beinganswered by an acknowledgement.

SDLC

SDLC is a control procedure that sends multipleblocks of data and returns a single acknowledgementfor many blocks, thereby increasing the amount oftime spent transmitting data. The bits that are putbefore and after the message at the transmitting endare removed at the receiving end, so only the messageis presented to the user.

Figure 8-7.—A ring network using the token passingaccess method.

The hardware chosen for the network plays a partin the choice of network protocol. Most users andmany of the vendors who build the clone type ofequipment would like to see universal interfaces,while others think that the availability of differentspecifications will lead to a proprietary set ofequipment, even though they favor the overall OSIspecifications.

LAN SYSTEMS

When you decide to install a LAN system, the typeof topology used in the initial wiring of the systemwill have a major effect on the type of system that canbe used. There are many LAN systems available,each with advantages and disadvantages. In thefollowing paragraphs, we briefly examine some of theavailable LAN systems.

The Institute of Electrical and ElectronicsEngineers (IEEE) has developed a set of standards forlocal-area networks. These standards encourage theuse of common approaches for LAN protocols andinterfaces. The IEEE LAN standards were developedby a committee of engineers and classified as the 802standards. The 802 standards are broken down evenfurther to define the protocols and topology used in aLAN. Some of the standards we are concerned withare the following:

I E E E 8 0 2 . 3 — C a r r i e r s e n s e m u l t i p l eaccess/collision detection (CSMA/CD)

IEEE 802.4—Token Bus

IEEE 802.5—Token ring

ETHERNET

The EtherNet local-area network was developedby Xerox, the Intel Corporation, and the DigitalEquipment Corporation. It became the model for thedevelopment of the IEEE 802.3 standard. Theoriginal standard defined a maximum throughput forEtherNet of 10 Mbit/s, but it has been revised tosupport throughput of much higher rates. Whenoperating over coaxial cable, EtherNet has a 20-Mbper second throughput speed. For high-demand

8-11

environments, such as engineering or graphics,EtherNet is often the choice. It is a bus topology anduses CSMA/CD protocol. It is available in thefollowing three versions: standard EtherNet, ThinNet,and twisted-pair EtherNet.

Standard EtherNet and ThinNet both use coaxialcab le . S tandard E therNet i s somewhat moreexpensive and more difficult to install than ThinNet,but it allows networking over greater distances withmore users. Twisted-pair EtherNet uses a distributedstar topology with wiring concentrator hubs, not thebus topology characterizing standard EtherNet andThinNet. Connecting more than 100 users on astandard EtherNet trunk or on a series of twisted-pairconcentrators is not uncommon, while ThinNet LANsusually support less than 50 users.

All versions of EtherNet create a LAN with highinterconnectivity options. A number of products areava i l ab le fo r connec t ing E therNet LANs tominicomputers and mainframe computers and forbridging to other LANs; examples are STARLAN,ARCnet, and IBM Token Ring Network.

STARLAN

STARLAN uses a star topology with a CSMA/CDprotocol. Its throughput speed is 1Mb per secondover twisted-pair cable. If buildings are already wiredwith twisted-pair cable meeting AT&T premisecabling specifications, STARLAN can be installedeasily. It is considered to be a low cost-per-usernetwork and its star topology makes it a flexiblenetwork.

ARCnet

ARCnet is a distributed star topology that uses atoken passing protocol and either twisted-pair orcoaxial cabling. Its throughput speed is 2.5Mb persecond. Although ARCnet does not conform to anIEEE standard, it closely resembles the 802.4 standardfor a token bus system. It can easily handle up to 75users. If user demand is low, it can handle additionalusers. It is considered an extremely reliable networkand it is easy to install, expand, and modify.

IBM Token Ring Network

The IBM Token Ring Network uses a star ringtopology, and is defined by the IEEE 802.5specification. It has a throughput speed of 4 Mbits persecond and 16 Mbit per second. This allows forflexible expansion of very large networks. Because ofits speed and token passing protocol, it is a goodchoice to meet high-volume requirements. It is asophisticated LAN technology developed by IBM tobe used with an IBM cabling system and it is currentlythe fastest growing installed network base. The starring topology also makes use of redundant circuits andloopbacks to handle breaks in the ring and results inhigh-fault tolerance on the network.

NETWORK OPERATING SYSTEMS

Network operating system software is necessary tocontrol the overall operations of the network. Carefulconsideration must be given to the various packageson the market to ensure the operating software is fullycompatible with your system, topology, and needs.

NETWORK OPERATING SYSTEM BASICS

The two basic components of the networkoperating system are the network operating systemserver and the workstation. The network server isusually a dedicated computer that runs the operatingsystem software and processes all requests forservices. The workstat ion computer runs theapplication software needed by the workstation userand establishes communications with the networkserver.

The network server operating system consists ofthe following five subsystems: the control kernel,the network interfaces, the file systems, the systemextensions, and the system services.

Control Kernel

The control kernel is the main subsystem of thenetwork operating software. The control kernelcoordinates the various processes of the othersubsystems. Some of the functions performed by thecontrol kernel are as follows:

Optimizing access to services by users

8-12

Maintaining status information of many of theprocesses

Error reporting

Service initialization and service terminationof workstations

Network Interfaces

The network interfaces provide the low-levelsubnet protocols and basic translation for bridginghardware drivers with the network operating system.In sophisticated systems, the network interfaces canalso provide for bridging a new network into anoperating network without having to rebuild theoperating system.

File Systems

The file system controls the way the data isorganized, stored, and retrieved from the storagesystems available to the network. The files may bestored on hard drives, RAM disks, or optical storagedevices, such as CD-ROM or write once, read many(WORM) drives.

File systems are generally designed to provideuniversal applicability. This means that the filesystem can be compatible with any applicationprogram’s expectation of file input/output protocol.When adaptable interfaces are used, the file systemcan appear to emulate a number of different filesystems.

System Extensions

The system extensions define the openness of thenetwork operating system and are used by third partydevelopers to produce add-on products . Theextensions are usually high-level protocol handlersthat perform operations, such as file access protocoltranslations required by different operating systems.The extensions available also include networkmanagement, system tools, and data-base services.

System Services

Network system services contain all services thatare not easily defined by any of the other areas of thenetwork. Examples of network services are security,system reliability features, error conditions, andaccess violations.

N E T W O R K O P E R A T I N G S Y S T E M SSOFTWARE

The most important job of a network operatingsystem (NOS) is to provide file service for theattached computers. This allows information retrievaland usage and the storage of data in a sharedenvironment. A NOS manages the other resourcesshared by the network and provides the followingfunctions:

Directory structure for shared hard diskstorage devices

File service for sharing and using data

Interface to the network for applicationsoftware/programs

The means by which the network managermanages the network and its users

Network security and data protection

Communications with other networks

The types of network operating systems includefull-featured, low-cost, and zero-slot operatingsystems.

Full-Featured Network Operating Systems

Most full-featured network operating systemsallow for high performance, flexibility, and excellentsecurity measures. They require a LAN administrator.They require network interface cards. Also, they canbe quite costly. Examples of a full-featured NOS areEtherNet, Novell’s NetWare, 3Com’s 3+Share, IBMToken Ring Network, and Banyan’s Vines.

8-13

Low-Cost Network Operating Systems Zero-Slot Network Operating Systems

Most low-cost network operating systems differ Zero- s lo t ne twork opera t ing sys tems a refrom full-featured systems only in the maximum appropriate only for networks with very few users andnumber of users accommodated on the network and Light usage. They are an inexpensive and simplethe number of security levels incorporated into the alternative to the NOSs that require expensiveoperating system. In general, they are much lower in network interface cards. Rather than requiring eachcost and are easier to install and use. Examples of workstation computer to have a NIC, the computer’slow-cost systems are STARLAN, ARCnet, 10Net, and RS-232 serial communications port and twisted-pairLANtastic. cables are used. Because of this, they are very slow

and offer limited file transfer abilities. They may notprovide disk sharing. An example of a zero-slotsystem is LANLink.

8 - 1 4

APPENDIX I

LIST OF ACRONYMS

ACDS —advanced combat direction system.

ACRO (or CRO) —auxiliary cathode readout,

ALT key —alternate key.

A/N —alphanumeric.

APA —all points addressable.

AM —amplitude modulation.

ASCII —American Standard Code for InformationInterchange.

ASTAB —automated status board.

ASW —antisubmarine warfare.

BC —broadcast.

BDU —basic display unit.

BER —bit error rate.

BITE —built-in test equipment.

BPS —bits per second.

C2P —Command and Control Processor.

CAG —central automated status board generator.

CCAEP —computer-controlled action entry panel.

CDB —central data buffer.

C-DITEG —common digital television graphicsgenerator.

CDS —combat direction system.

CED —console electronic drawer.

CEG —central equipment group.

CGA —color graphics adapter.

CIGARS —console internally generated andrefreshed symbols.

CIU —computer interface unit.

CONICS —circles and ellipses.

CP —clock pulse.

CPS —cycles per second.

CRO —TV monitor.

CRT —cathode-ray tube.

CTRL —control.

dB —decibels.

DCC —display control console.

DCI —direct computer interface.

DDEU —digital data entry unit.

DDI — (1) digital data indicator; (2) digital displayindicator.

DITEG —digital television graphics generator.

DIV —diversity.

DLRP —Data Link Reference Point.

DMU —display multiplexer unit.

DRAC —digital radar azimuth converter.

DSC —digital scan converter.

DTS —data terminal set.

EDAC —error detection and correction.

EF word —external function word.

EGA —enhanced graphics adapter.

EMI/RFI —electromagnetic interference/radiofrequency interference.

EPROM —erasable, programmable read-onlymemory.

ESC key —escape key.

FM —frequency modulation.

AI-1

GUI —graphic user interface.

HF —high frequency.

HVPS —high voltage power supply.

HZ —hertz.

I/O —input/output.

IFF/SIF —identification, friend or foe/selectiveidentification feature.

JTIDS —Joint Tactical Information DistributionSystem.

J-SERIES MESSAGE —The fixed formatmessages containing tactical data andcommands that are used to exchangeinformation over the JTIDS system.

JU —JTDS Unit.

LCD —liquid crystal display.

LCLV —liquid crystal light valve.

LED indicator —light-emitting diode indicator.

LINK-4A —The tactical digital data link forcontroller-to-controlled aircraftcommunications.

LINK-11 —The tactical digital data link forcommunications among a multiple number ofunits.

LINK-16 —The tactical digital data link forcommunications among a multiple number ofunits. This link is a secure, jam resistant,nodeless, high-capacity link that uses theJTIDS terminal.

LSB —Lower Side Band.

LSD —large screen display.

LVPS —low voltage power supply.

MDA —Monochrome Display Adapter.

M-SERIES MESSAGES —Link-11 messages.

NCS —Net Control Station.

NCT —Net Cycle Time.

NICP —Network Interface Control Program.

N-SERIES MESSAGES —The “normalized”messages exchanged between the C2Pcomputer and the ADCS computer.

NTDS —naval tactical data system.

ODR —output data request.

OJT —on-the-job training.

OSC —operations summary console.

PA/SG —pulse amplifier/symbol generator.

PC —personal computer.

PEFT —peripheral equipment functional test.

PIO —peripheral I/O

PIXEL —picture element.

PMS —planned maintenance system.

POFA —programmed operational functionalappraisal.

PPI —plan position indicator.

PPLI —precise participant location andidentification.

PPU —projection plotting unit.

PROM —programmable read-only memory.

PU —participating unit.

RAC —radar azimuth converter.

RAM —random access memory.

RC —Roll Call.

RDDS —radar data distribution switchboard.

RELNAV —relative navigation.

RF —radio frequency.

RGB —red, blue, green.

ROM —read-only memory.

ROM BIOS —ready-only memory basic inputoutput system.

R-SERIES MESSAGES —Link-4A messagesfrom the controlled aircraft that are sent inresponse to a control message.

AI-2

SAC —sonar azimuth converter.

SCG —sensor converter group.

SDDS —sensor data distribution switchboard.

SG —symbol generator.

SRAC —synchro radar azimuth converter.

SVGA —super video graphics array.

TDM —tactical DITEG module.

TDS —tactical data system.

TFT —thin film transistor.

TMG —test message generator.

TN —track number.

TQ —track quality.

TSLO —third salvo lock out.

TTL —transistor-transistor logic.

TVC —television converter group.

TVSC —television scan converter.

UHF —ultra-high frequency.

USB —upper side band.

V/C word —velocity/category word.

VDT —video display terminal.

VFK panel —variable function key panel.

VGA —video graphics array.

V-SERIES MESSAGES —Link-4A controlmessages sent from the controlling station tothe controlled aircraft.

VSS —video signals simulator.

XGA —extended graphics array.

AI-3

APPENDIX II

REFERENCES USED TO DEVELOPTHE TRAMAN

NOTE: Although the following references were current when this TRAMAN waspublished, their continued currency cannot be assured. Therefore, you need to be surethat you are studying the latest revision.

AN/PRC-113, Harris RF Communications 31R2-2PRC113-1, 1680 University Avenue,Rochester, New York, NY, (no date).

AN/PRC-117, Harris RF Communications 31R2-2PRC117-1, 1680 University Avenue,Rochester, New York, NY, (no date).

Black, Uyless D., Data Networks, Concepts, Theory, and Practice, Prentice-Hall, Inc.,Englewood Cliffs, NJ, 1989.

Communications Link Interoperability Planning System (CLIPS), Systems Integration and TestDivision, Naval Electronics Systems Command, Engineering Activity, St. Inigoes, MD,1988.

Data Communication System AN/USC-30, NAVSEA 0967-563-9010, GovernmentTelecommunications Division, Collins Radio Group, Rockwell International, Dallas, TX,1975.

Durr, Michael, Networking Personal Computers, 3d ed, Que Corp., Carmel, IN, 1989.

Electronics Installation and Maintenance Book, Communications Handbook, NAVSEASE000-00-EIM-010, Naval Sea Systems Command, Washington, DC, Sep 1979.

Electronics Technician 3 & 2, NAVEDTRA 10197, Naval Education and Training ProgramManagement Support Activity, Pensacola, FL, 1987.

Hancock, Bill, Designing and Implementing Ethernet Networks, QED Information Sciences, Inc.,Wellesley, MA, 1988.

Heath, Steve, Effective PC Networking, Butterworth-Heinemann Ltd., Oxford, England, 1993.

Instruction Manual, Data Terminal Set, AN/USQ-59(V)2, SPAWAR 0967-LP-563-9020, Spaceand Naval Warfare Systems Command, Washington, DC, 1973.

Line of Sight Microwave and Tropospheric Scatter Communication Systems, NAVELEX0101,112, Naval Electronics Systems Command, Washington, DC, 1972.

Link-11 Seminar for Operators and Technicians, Instructor Notes, Link-11 Waterfront Seminar,Logicon, Inc., San Diego, CA, 1990.

AII-1

LMS-11 Troubleshooter’s Guide for Link-11 Operations, Logicon, Inc., San Diego, CA, 1990.

Navy UHF Satellite Communications System Description, FSCS-200-83-1, Naval Ocean SystemsCenter, San Diego, CA, 1991.

Operating and Service Manual, C-12428/USQ-125 Control Unit, Cedar Technology Inc.,Longmont, CO, 1995.

Operation and Maintenance Instructions, MX-512PV, Link-11 Data Terminal, General AtronicsCorp., Philadelphia, PA, 1992.

Operation and Maintenance Instructions, Organizational Level, Link 11 Data Terminal SetAN/USQ-76(V)3, SPAWAR EE640-DW-OMI-0lB/El10-USQ76V3, Space and NavalWarfare Systems Command, Washington, DC, 1990.

Operation and Maintenance Manual for the Link Monitor System (LMS-4) for Link-4A, Logicon,Inc., San Diego, CA, 1990.

Operator’s Manual, Digital Message Device Group, TM 11-5820-887-10, U.S. ArmyCommunications-Electronics Command, Fort Monmouth, NJ, 1982.

Operator’s Manual, Radio Set AN/PSC-3, EE125-JC-OPI-010, U.S. ArmyCommunications-Electronics Command, Fort Monmouth, NJ, 1988.

Operator/O-Level Maintenance Training Course, Trainee Guide for the Link Monitor System,AN/TSQ-162(V)1, Logicon, Inc., San Diego, CA, 1990.

Preliminary Technical Manual, System Maintenance, Organization Level, AN/UYQ-62(V)1, 2,Command and Control Processor (C2P) Subsystem, SPAWAR EE600-AB-SLM-010), Spaceand Naval Warfare Systems Command, Washington, DC, 1992.

Radio Set AN/PRC-104(A) Technical Manual, TM 11-5820-919-12, U.S. ArmyCommunications-Electronics Command, Fort Monmouth, NJ, 1986.

Shipboard Electronics Material Officer, NAVEDTRA 12969, Naval Education and TrainingProgram Management Support Activity, Pensacola, FL, 1992.

System Operation and Maintenance Manual, AN/USQ-74, 74A, Data Terminal Set, SPAWAREE600-AA-OMI-010, Space and Naval Warfare Systems Command, Washington, DC, 1990.

Technical Manual, Installation, Operation, and Maintenance with Illustrated Parts Breakdown,Computer Adapter MX-9222/U, NAVSEA 0967-LP-563-9060, Naval Sea Systems Command,Washington, DC, 1977.

Technical Manual, Operation, Maintenance with Illustrated Parts Breakdown, AddressControl - Indicator, C-9062/U, NAVSEA 0967-LP-563-9040, Naval Sea SystemsCommand, Washington, DC, 1977.

AII-2

Technical Manual, Operation, and Maintenance with Illustrated Parts Breakdown, Data-Terminal Set Control, C-9063/USQ-59, NAVSEA 0967-LP-563-9050, Naval Sea SystemsCommand, Washington, DC, 1977.

Technical Manual, Operation, Maintenance Manual with Illustrated Parts Breakdown, DigitalTo Analog Converter, CV-2969A(P)/U, NAVSEA 0967-LP-563-9070, Naval Sea SystemsCommand, Washington, DC, 1977.

Technical Manual, Volume 1, Digital Data Communications Control Set, AN/SSW-1D(U),NAVSEA 0967-LP-555-401, Naval Sea Systems Command, Washington, DC, 1973.

Technical Manual, System Operation and Maintenance Instructions, Organization Level, LinkMonitor System, AN/TSQ-162(V)1, SPAWAR EE- 190-AB-OMI-010/TSQ-162(V) 1, Spaceand Naval Warfare Systems Command, Washington, DC, 1989.

Understanding Link-11, A Guidebook for Operators, Technicians, and Net Managers, NavyCenter for Tactical Systems Interoperability, San Diego, CA, 1991.

Understanding Link-16, A Guidebook for New Users, Logicon, Inc., San Diego, CA, 1994.

User’s Manual, Link-11 Monitor System, Rack-mountable (LMS-11R), Logicon, Inc., San Diego,CA, 1990.

VLF, LF, and MF Communications Systems, NAVELEX 0101,113, Naval Electronic SystemsCommand, Washington, DC, 1972.

Woodward, Jeff, The ABC’s of Novell NetWare, Sybex Inc., Alameda, CA, 1989.

AII-3

INDEX

ACommunications Link Interface Planning System,

2-28

Address control indicator, 4-16

AN/SSW-1D/E Data Terminal Set, 6-5

AN/USQ-125 Data Terminal Set, 7-1

Antenna couplers, 4-4

Antennas, 4-5

ARCnet, 8-12

Asynchronous transmission, 1-7

C

Carrier Aircraft Inertial Navigational System, 6-3

Command and Control Processor, 7-11

System configuration, 7-12

Communications theory

amplification, 1-10

antennas, 1-13

baud, 2-16

dc circuits, 2-16

emissions, 1-4

frequency diversity, 2-19

frequency spectrum, 1-2

intermodulation distortion, 2-19

line-of-sight, 2-12

modulation, 1-4

multiplexing, 2-13

radio communications, 1-1

safety, 1-1

satellite, 3-1

space diversity, 2-19

syncros/servos, 1-13

system, 2-1

transceivers, 1-11

tropospheric scatter, 2-13

TTY/facsimile, 2-15

Communications Systems Equipment Coniiguratiom

AFTS, 2-23

Fleet Satellite, 3-4

hf, 2-5

lf, 2-4

microwave, 2-10

RFCS, 2-22

SAS, 2-14

Shf, 2-9

uhf, 2-8

Vhf, 2-7

vlf, 2-3

CP-2205(P)(V)/USQ-125 Data Terminal, 7-1

E

Enhanced Link Quality Analysis (ELQA), 7-2

Equipment

ancillary, 1-12

frequency standards, 2-18

portable and pack radios, 2-24

SATCOM, 3-23

TTY sets, 2-20

EtherNet, 8-11

F

FLTSATCOM

control subsystem, 3-16

CUDIXS subsystem, 3-6

DAMA subsystem, 3-15

Fleet Broadcast subsystem, 3-4

NAVMACS subsystem, 3-6

OTCIXS subsystem, 3-14

Secure Voice subsystem, 3-10

INDEX-1

FLTSATCOM—Continued

SSIXS subsystem, 3-9

TACINTEL subsystem, 3-11

TADIXS subsystem, 3-13

teletypewriter subsystem, 3-13

FLTSATCOM shorebased terminals, 3-3

I

IBM Token Ring, 8-12

J

Joint Tactical Information Distribution

System (LINK-16), 7-4

Link-16 data exchange, 7-6

Link-16 nets, 7-6

JTIDS terminal, 7-9

JTIDS architecture, 7-6

JTIDS, 7-4

L

LAN topologies, 8-7

Distributed star network, 8-9

Linear bus network, 8-7

Ring network, 8-9

LAN protocols, 8-10

LAN access methods, 8-10

Contention, 8-10

Token passing, 8-10

Link-11 Data Terminal Set, 4-4, 4-11

Audio tone generation and characteristics, 4-11

Controls and indicators, 4-13

Mode control panel, 4-13

TADIL A control panel, 4-15

Error detection and correction, 4-10

Link-11 message formats, 4-8

Broadcast mode message, 4-9

Call-up(interrogation) message, 4-9

Link-11 message formats—Continued

NCS report and call-up, 4-9

Picket reply message, 4-9

Roll call message, 4-8

Short broadcast message, 4-9

Link-11 Monitoring System(LMS-11), 5-6

Carrier suppression display, 5-17

Link monitor mode, 5-9

Net display, 5-12

Operation and displays, 5-9

PU display, 5-16

Spectrum display, 5-18

Status display, 5-11

System initialization, 5-9

System configuration, 5-7

Link-11 Net operating modes, 4-5

Broadcast, 4-6

Net test, 4-6

Net synchronization 4-6

Radio silence, 4-7

Roll call, 4-6

Short broadcast, 4-7

Link-11 system overview, 4-2

Link-16 new capabilities, 7-6

Link-4A CDS system, 6-1

Link-4A message formats, 6-3

Control messages, 6-4

Reply messages, 6-4

Test messages, 6-4

Link-11 message, 4-7

Information segment, 4-8

Phase reference frame, 4-7

Preamble, 4-7

Start code, 4-8

Stop code, 4-8

Link-11 security device, 4-3

INDEX-2

Link Monitor System(LMS-4), 6-6 Remote control unit, 7-4

Local-area network hardware, 8-3

M

Maximum useable frequency(MUF), 7-3

Multi-frequency link, 7-3

Multi-tone waveform link, 7-2

Multi-station POFA, 5-5

N

Network Operating Systems, 6-14

O

Open System Interconnection (OSI) Reference Model,6-6

R

Receivers

AM superheterodyne, 1-9

characteristics, 1-8

FM superheterodyne, 1-9

functions, 1-7

microwave, 2-12

ssb, 1-10

Recognizing Link-11 Problems, 5-18

S

Satellites, 3-21

Shipboard Gridlock System, 4-3

Single station POFA, 5-3

Single-tone waveform link, 7-2

STARLAN, 8-12

T

Tempest

black criteria, 2-24

red criteria, 2-24

Transmitters microwave, 2-10, 2-11

AM, 1-16

CW, 1-5

FM, 1-6

fundamentals, 1-4

portable and pack, 2-24

ssb, 1-6

INDEX-3

Assignment Questions

Information: The text pages that you are to study areprovided at the beginning of the assignment questions.

ASSIGNMENT 1Textbook Assignment: “Fundamentals,” chapter 1, pages 1-1 through 1-13; and

“Systems Equipment Configurations,” chapter 2, pages 2-1through 2-27.

1-1. What type of equipment is usedto coordinate the activities offleet units by linking them witheach other and shore stations?

1. Radio2. Weather3. Radar4. Navigation

1-2. Radio is the transmission andreception of electronic impulsesor signals through space bymeans of what type of waves?

1.2.3.4.

1-3.

1.2.3.4.

PulsedPhasedElectromagneticElectrostatic

Who is ultimately responsiblefor safety?

COCMCLCPOEveryone

1-4. What are the basic requirements

1.2.3.4.

of a communications system?

Transmitter and receiverTeletype and converterTransmitter and handsetReceiver and handset

1-5. AN/UCC-1, AN/URA-17, and CV-2460are examples of what type ofshipboard equipment?

1. Ancillary2. Auxillary3. Special4. Terminal

1-6. For efficient transmission,which of the following frequencybands require(s) high power andlong antennas?

1. ELF only2. VLF only3. LF only4. ELF, VLF, and LF

1-7. Which of the following frequencybands has limited naval use?

1. HF2. MF3. UHF4. VHF

1-8. What does the abbreviation “los”commonly mean?

1.2.3.4.

Loss-of-signalLine-of-sightLoss-of-sightLine-of-signal

1-9. The super-high-frequency band isused extensively in what ofcommunications?

1. Teletype2. Repeater3. Microwave4. Computer

1-10. The emission class of an rftransmitter is based on whatcharacteristic?

1. Modulation2. Power3. Sensitivity4. Frequency

1-11. An FM signal should remainconstant in (a) whatcharacteristic and change onlyin (b) what characteristic?

1. (a) Frequency (b) amplitude2. (a) Frequency (b) modulation3. (a) Amplitude (b) frequency4. (a) Amplitude (b) modulation

1-12. What type of modulation isespecially suited for use intime-division multiplexing?

1. Amplitude2. Frequency3. Phase4. Pulse

1

1-13 ● For modern communication needs,CW is not a preferred method.Why is this true?

1. CW is slow2. CW is complicated3. CW is expensive4. CW is noisy

1-14 ● In an FM transmitter, the audiosignal shifts the carrierfrequency in what network?

1. Audio-shift2. Phase-shift3. carrier-shift4. Band-shift

1-15. In a ssb transmitter the carrieris removed to concentrate thepower in the sideband(s) .

1. True2. False

1-16. Which of the four receiverfunctions involves extraction ofthe modulation from the rfsignal?

1. Detection2. Reception3. Reproduction4. Selection

1-17 ● Which of the four receivercharacteristics requirecompromise because of bandpassrequirements ?

1. Selectivity and noise2. Selectivity and fidelity3. Noise and fidelity4. Noise and sensitivity

1-18. What term is used to describereceiver amplification?

1. Fidelity2. Noise3. Gain4. Power

1-19. The term “dBm” is based on whatstandard reference level?

1. 1 watt2. 1 volt3. 1 milliwatt4. 1 millivolt

1-20. Normal power out is 100 watts.During PMS, you discover thatpower out has dropped by 3dB.What is the new power out?

1. 97 watts2. 70 watts3. 50 watts4. 3 watts

1-21. How many radio set controls canbe paralleled to onetransmitter/ receiver group?

1. One2. Two3. Three4. Four

1-22 ● To transfer control of switchedcircuits to another transmitteror receiver switchboard, youshould use what switch position?

1. Off2. X3. Five4. Six

1-23. Which of the following terms isused for a machine that operatesas a single-phase transformer?

1. Servo2. Synchro3. Gyro4. Compass

1-24. When you use subdivisions toassign reference designators toequipment, what is thedesignator of the (a) largestsubdivision and (b) smallestsubdivision?

1. (a) System (b) set2. (a) Set (b) unit3. (a) System (b) part4. (a) Unit (b) assembly

1-25. Extremely-low-frequencytransmission is primarilydirected at which of thefollowing users?

1. Aircraft2. Shore installations3. Submarines4. Surface ships

2

1-26.

1-27.

1-28.

1-29.

1-30.

The very-low-frequency receivesystem is designed to receivewhat types of signals?

1. AM and FM2. FSK and CW3. FSK and ICW4. SSB and FSK

The AN/FRT-72 (if) transmitteris used to provide (a) how manychannels of frequency-divisionmultiplex rtty traffic over (b)what type of fleet broadcastsystem at (c) what type ofpower?

1. (a) Eight (b) multichannel(c) high

2. (a) Eight (b) singlechannel(c) high

3. (a) Four (b) multichannel(c) low

4. (a) Four (b) multichannel(c) high

HF communications from shore-based transmitters to ships atsea using frequency and spacediversity is an example of whichof the following types ofsystems?

1. Fleet broadcast2. Point-to-point3. Ground-to-air4. ship-to-shore

Which one of the followingequipment would you use to matcha transmitter’s output impedanceto an antenna’s input impedance?

1. CV-24602. SB-988/SRT3. AN/UCC-14. AN/URA-38

The AN/VRC-80 is not just a vhftransmitter or receiver. Whatis the name given to a piece ofequipment that performs bothfunctions?

1. Transducer2. Multiplexer3. Retransmitted4. Transceiver

1-31.

1-32.

During UHF secure voicetransmission, the operator usesa secure voice remote phoneunit. What is the common termfor this unit?

1. RPS2. RPU3. SVP4. SPU

which of the followingcombinations of radio-relaysystems provides (a) one-waycommunications and (b) two-waycommunications?

1. (a) Simplex (b) multiplex2. (a) Duplex (b) multiplex3. (a) Simplex (b) duplex4. (a) Duplex (b) simplex

1-33 ● What term is normally used formicrowave transmitter inputsignal?

1. Baseband signal2. Emphasis signal3. Insertion signal4. Linear signal

1-34. In a microwave transmitter, thelinearize couples a portion ofthe output power back to theklystron. This allows formodulation densities as high as1200 channels and compensatesfor what klystron deficiency?

1. Nonlinearity2. Oscillations3. Overheating4. Selectivity

1-35. In a typical microwave receiver,what is the standardintermediate frequency?

1. 40 MHz2. 50 MHz3. 60 MHz4. 70 MHz

1-36. Which of the following methodsare usually used for microwavecommunications?

1. Los and troposcatter2. Los and satcom3. Troposcatter and satcom4. Troposcatter and shortwave

3

1-37.

1-38.

1-39.

1-40.

1-41.

1-42.

By which of the followingmethods can you increase themaximum number of intelligiblesignals transmitted on a singlepath?

1. Modulation2. Single audio mixing3. Multiplexing4. Single signal splitting

Which of the following communi-cations methods involvessubdividing a channel intosmaller segments of equal sizeand placing a signal in eachsubchannel?

1. FDM2. TDM3. DFM4. DTM

Which of the followingrequirements does SAS satisfy?

1. Nonsecure voicecommunications

2. Secure voice communications3. Voice signal switching4. All of the above

How many crypto and plainsubsystems are used within SAS?

1. Five2. Two3. Three4. Four

One mode of teletypewriteroperation is the synchronousmode. What other mode is usedfor basic teletypewriteroperation?

1. Asynchronous2. Bisynchronous3. Nonsynchronous4. Trisynchronous

What is the name of the five-unit code that includes mark andspace signals and is used inteletypewriter operation?

1. Baud2. Baudot3. ASCII4. Morse

4

1-43. Which of the following problemsis reduced by not using startand stop signals in thesynchronous teletypewriter mode?

1. Converted signal2. Delayed signal3. Distorted signal4. Lost signal

1-44. Which of the following termsaccually pertains only tomodulation rate?

1. Baud2. Words per minute3. Bites per second4. Words per second

1-45. In neutral tty operation,current flow and no current flowrepresent the mark and spaceconditions. In polar ttyoperation what is the conditionof the line current?

1. It is always absent2. It is always positive3. It is always negative4. It is always present

1-46. What device is used to changetty dc pulses into mark andspace signals to modulate thetransmitter carrier wave?

1. Detector2. Keyer3. Modulator4. Transformer

1-47. After the tty signal isreceived, what device(s) must beused to change the signal backto dc pulses?

1. Convertor2. Receiver3. Both 1 and 2 above4. Keyer

1-48. The Navy’s two basic RATTsystems are AFTS and RFCS. Whatis the RFCS system commonlycalled?

1. ASK2. FSK3. PSK4. RSK

1-49. What device provides loopingcurrent for the tty?

1. A solid state power supply2. A generator3. An alternator4. The tty battery

1-50. What is/are used to interconnectall the tty equipment in anyconfiguration needed?

1. Multiple cabling2. Wire runs3. TTY panel4. Switching resistors

1-51. Which of the following methodsis/are used to reduce fading andinterference in long-rangecommunications?

1. Frequency diversity2. Space diversity3. Both 1 and 2 above4. Ionospheric inversion

1-53. During unpatching, pulling whichplug from its tty panel jackfirst will produce a dangerousdc voltage on the exposed plug?

1. Looping2. Set

1-54. How many rotary switch positionswill you find on a remotetransmitter control unit?

1. One2. Two3. Three4. Four

1-55. In AFTS, to what does the term“half-duplex” refer?

1. “Send only”2. “Receive only”3. “Send or receive”4. All of the above

1-52. What type of frequency diversityis used for multichannelbroadcasts?

1. Signal2. Space3. Triple4. Tone

5

ASSIGNMENT 2Textbook Assignment: “Systems Equipment Configurations,” chapter 2, pages 2-27

through 2-33; “Satellite Communications,” chapter 3,pages 3-1 through 3-35.

2-1.

2-2.

2-3.

2-4.

2-5.

Which of the following methodsshould you use to transmitprinted text?

1. Facsimile2. Single tone3. Multiplexing4. Sequencing

In which of the followingpublications can you findinformation on TEMPESTrequirements?

1. MIL-STD-16502. MIL-STD-16603. MIL-STD-16704. MIL-STD-1680

What is the designator of anyconductor intended to carryclassified plain languageterminating in RED equipment orthe RED side of cryptoequipment?

1. Coded red2. Primary red3. Secondary red4. Terminal red

Of the following radios, whichis popularly known as the“Gibson girl”?

1. AN/CRT-3A2. AN/PRC-773. AN/PRC-964. AN/PRC-117

Which of the following radiosprovides homing and two-wayvoice communications betweenliferafts and searching ships?

1. AN/CRT-3A2. AN/PRC-773. AN/PRC-964. AN/PRC-104

2-6. Which of the following radiosis particularly useful duringtactical black-out operations?

1. AN/PRC-962. AN/PRC-1043. AN/PRC-1174. AN/PSC-3

2-7. Which of the following radioshas frequency hoppingcapability?

1. AN/PRC-962. AN/PRC-1043. AN/PRC-1174. AN/PSC-3

2-8. The use of frequency hoppinghas certain advantages. Oneadvantage is that the signal isdifficult to detect. How isthis accomplished?

1. No single carrier is used2. No modulation is used3. No signal amplification is

used4. No multiplexing is used

2-9. One important feature of theAN/PSC-3 uhf radio is that itcan interface directly with vhfradios. What is the purpose ofthis interface?

1. To provide a satellite linkfor vhf radios

2. To make everyone use uhfinstead of vhf

3. To provide a keyer for thevhf radios

4. To provide dual channelcapability for the vhfradios

6

2-10. DMDG messages are sent at 300or 1200 baud in the satellitemode and 266.6 baud whenconnected to AN/PRC-70/74.When these messages arereceived, they are read on adisplay screen. Which of thefollowing is the device used totype and read these messages?

1. KY-823/P2. KY-798/P3. KY-283/P4. KY-879/P

2-11. What system was specificallydesigned to provide solutionsto equipment planning byautomatically determining thebest system that eachparticipant in a communicationslink should use?

1. CLEPS2. CLIPS3. CLSPS4. CLWPS

2-12. Of the two terms listed below,which one refers to reflectionof radio signals back to earthby a satellite?

1. Active2. Passive

2-13. Which term refers to receptionand retransmission?

1. Active2. Passive

2-14. Which of the following termsrefers to transmissionsreceived from a satellite?

1. Uplink2. Downlink3. Modelink4. Backlink

2-15. SATCOM links are only slightlyaffected by what phenomenaassociated with hf propagationdifficulties?

1. Atmospheric2. Cosmic3. Siezemic4. Vortic

2-16. Trained crews can set up whattype of satellite earthterminals within hours toestablish communications inremote areas?

1. Crisis2. Defensive3. Mobile4. Partial

2-17. Of the following factors,which, if any, limit the use ofa satellite communicationssystem?

1. Orbital parameters andtechnical characteristics

2. Transmitter power andreceiver sensitivity

3. Both 1 and 24. None of the above

2-18. What purpose doesCUDIXS/NAVMACS serve?

1. Provides an extension toterrestrial teletypewriternetworks

2. Provides status reportingand management of systemassets

3. Provides a communicationslink between submarines andshore terminals

4. Provides a communicationsnetwork for transmittinggeneral-service messagetraffic between ships andshore installations

2-19. How many NCTAMS have primaryresponsibility forcommunications via satellite?

1. One2. Two3. Three4. Four

2-20. Subsystems consist of twoparts. What are they?

1. Baseband equipment; rfterminal

2. Multiplexing equipment;satellite

3. Satellite; rf terminal4. Transmitters; receivers

7

2-21. In modes 1 through 6, what arethe uplink and downlinkfrequency bands used in FleetSatellite Broadcast?

1. Hf; shf2. Uhf; hf3. Uhf; shf4. Shf; uhf

2-22. What system do subscribers useto receive Fleet SatelliteBroadcast?

1. AN/BRA-12. AN/FRT-13. AN/SSR-14. AN/VRC-1

2-23. What is the minimum number ofbroadcast channels that NAVMACSguards automatically?

1. One2. Two3. Three4. Four

2-24. What is the bandwidth (in kHz)of the satellite channelsallocated to CUDIXS/NAVMACS?

1. 102. 153. 204. 25

2-25. What term is associated with asubmarine commander’s abilityto receive messages viasatellite at scheduledintervals?

1. Group broadcasts2. Interval broadcasts3. Network broadcasts4. Timed broadcasts

2-26. Secure voice uses digitizedvoice with a 3-kHz voicechannel. What type of voicemodulation does this describe?

1. Multiband2. Narrowband3. Singleband4. Wideband

2-27. When using Secure Voice, a shipmust contact what authoritybefore initiatingcommunications with a shorecommand?

1. Fleet controller2. Group controller3. Net controller4. Voice controller

2-28. Which of the following is asubsystem specifically designedfor special intelligencecommunications?

1. OTCIXS2. TADIXS3. TACINTEL4. FLTSATCOM

2-29. TADIXS-equipped surface shipsand submarines operate in whatmode(s)?

1. Receive only2. Transmit only3. Transmit and receive

2-30. What subsystem is used inconjunction with TADIXS totransmit OTH-T data from thefleet to other ships and shorecommands?

1. OTCIXS2. SSIXS3. TACINTEL4. FLTSATCOM

2-31. Because the reception of TADIXSinformation by a ship does notrequire an acknowledgement, theship can l operate in what typeof environment and stillreceive message traffic?

1. Emission control2. Emission quiet3. Transmit control4. Transmit quiet

2-32. What system was developed tomultiplex several users on one25-kHz satellite channel?

1. MSAS2. DAMA3. VINSON4. NCTAMS

8

2-33. What term is used to describehow the Demand AssignedMultiple Access data stream isformatted?

1. Frame2. Picture3 Segment4. Window

2-34. In the DAMA multiplexed datastream, which slot is used totest for communications error?

1. Data2. Link3. Ranging4. Return channel

2-35. What are all DAMA multiplexertransmit times referenced to?

1. The controller2. The satellite3. The transmitter4. The Vocoder

2-36. Which of the followingequipments is used as the DAMAmultiplexer?

1.2.3.4.

DM-1217B/UTD-1271B/UDM-1271B/UTD-1217B/U

2-37. Who performs day-to-day controland operation of navalsatellite communicationsassets?

1. Chief of Naval Operations2. Satellite Operations Command3. Naval Space Command4. Naval Computer and

Telecommunications Command

2-38. Of the 23 uhf communicationschannels each FLTSATCOMsatellite has, how many onededicated to Navy use?

1. 12. 53. 104. 15

2-39.

2-40.

2-41.

2-42.

2-43.

2-44.

How many FLTSATCOM satelliteshave ehf packages installed?

1. One2. Two3. Three4. Four

LEASAT satellites have fewer25-kHz channels than FLTSATs.What ground-based system dothey use to maintaincommunications efficiency?

1. DAMA2. MSAS3. PSAS4. VINSON

What is the replacementsatellite for GAPFILLER,FLTSATCOM, and LEASAT?

1. UHF F/O2. UFO F/O3. SHF F/O4. SRP F/O

The AN/FSC-79 satellitecommunications terminaltransmits on what band?

1. Ehf2. Hf3. Shf4. Uhf

Which of the following isanother term used to describethe shf communications band?

1. A-band2. S-band3. U-band4. X-band

The AN/WSC-5(V) uhf transceiveris capable of usingdifferentially encoded phase-shift-keying and what othertype of modulation?

1. AM2. CW3. FM

9

2-45.

2-46.

2-47.

2-48.

2-49.

Which of the following radiosis the primary shipboard losand satellite transceiver?

1. AN/WSC-32. AN/WCS-33. AN/WSC-54. AN/WCS-5

The AN/WSC-3 transceiver hastwo rf output levels. One ofthese is 30 watts. What is theother rf output level?

1. 50 watts2. 100 watts3. 150 watts4. 200 watts

What shipboard system is usedto receive Fleet SatelliteBroadcast?

1. AJS/BRC-12. AN/SRR-13. AN/SSR-14. AN/BRR-1

Which of the following is aspread spectrum type modem andis used with the AN/FSC-79satellite communicationsterminal?

1. OM-33A/USC2. OM-43A/USC3. OM-51A/FR4. OM-61A/FR

Of the two processors listedbelow, which one is used in theTADIXS subsystem?

1. AN/UYK-20(V)2. AN/UYK-44(V)

1.2.3.4.

2-50. The AN/USQ-69(V) data terminalset is currently used with whattwo subsystems?

SSIXS/OTCIXSTACINTEL/NAVMACSNAVMACS/TADIXSOTCIXS/TADIXS

2-51. Audio digital converterCV-3333/U is used primarily asan analog-to-digital converterfor what type of communica-tions?

1. Analog voice2. Crypto voice3. Secure voice4. Unsecured voice

2-52. Where are the system interfaceconnectors installed on theElectrical Equipment RackCY-7597/WSC-3?

1. On the back panel2. On the front panel3. On the side panel4. On the top panel

2-53. DAMA-equipped shoreinstallations use the OK-481(V)2/FSC Control MonitorGroup to interface TD-1271B/Us,AN/WSC-5(V)s, and basebandequipment. It can accommodateup to how many TD-1271B/Us?

1. 112. 123. 134. 14

10

ASSIGNMENT 3

Textbook Assignment: “The Link-11 System,” chapter 4, pages 4-1 through 4-18.

3-1. Link-11 is designated as whichof the following types oftactical data information link?

1. TADIL A2. TADIL C3. TADIL J4. Teletype

3-2. Link-11 communications canoperate with which of thefollowing radios?

1. HF only2. UHF only3. Either HF or UHF4. VHF only

3-3. When Link-11 is operated withUHF radio, it is capable ofover-the-horizoncommunications.

1. True2. False

A. CDS Digital ComputerB. SGS ComputerC. Cryptographic DeviceD. Data Terminal SetE. Communications SwitchboardF. Radio Set

Figure 3A.

IN ANSWERING QUESTIONS 3-4 THROUGH3-11, SELECT FROM FIGURE 3A THEEQUIPMENT THAT PERFORMS THE FUNCTIONDESCRIBED IN THE QUESTION. ITEMS INTHE LIST MAY BE USED MORE THAN ONCE.

3-4. Selects the HF or the UHFtransceiver.

1. B2. C3. D4. E

3-5. Encrypts parallel data from theCDS computer and passes theencrypted data to the dataterminal set.

1. A2. B3. C4. D

3-6. Correlates reported positionsof local and remote tracks.

1. A2. B3. C4. D

3-7. Outputs 24-bit data words tothe security equipment via theSGS computer.

1. A2. B3. C4. D

3-8. Multiplexes and modulatesparallel data into audio tones.

1. A2. B3. C4. D

3-9. Receives the audio tone packagefrom the data terminal set andtransmits the tones.

1. C2. D3. E4. F

3-10. Demodulates the audio tones andchecks the six hamming bits fortransmission errors.

1. A2. B3. C4. D

11

3-11.

3-12.

3-13.

3-14.

3-15.

Decrypts the 24-bit data wordand sends it to the CDScomputer.

1. A2. B3. C4. D

Which of the followingfunctions is performed by anantenna coupler?

1. Amplification of the HFradio signal

2. Impedance matching of theantenna and the radio set

3. Conversion of atmosphericelectromagnetic energy to RFcurrent

4. Coupling of the dataterminal set to the radio

The size of an antenna isdetermined by which of thefollowing factors?

1.2.3.4.

The operating powerThe operating frequencyThe range of the receiverThe type of data beingtransmitted

The frequency range of anantenna can be extended byadding which of the followingfactors?

1. A resistive load only2. A capacitive load only3. An inductive load only4. Either a capacitive or an

inductive load

Which of the followingfunctions is NOT performed bythe data terminal set?

1. Generating the radio key-line signal

2. Converting digital data toaudio tones

3. Encrypting CDS computer data4. Converting audio tones to

digital data

3-16. The data terminal setcommunicates with the radio setvia which of the followingdevices?

1. The communicationsswitchboard

2. An antenna coupler3. The cryptographic device4. The SGS computer

3-17. Which of the following radiofrequency modulation methods isused to minimize propagation-caused signal loss during HFLink-11 operations?

1. Quadrature phase-shiftmodulation

2. Frequency modulation3. Phase modulation4. Amplitude modulation

independent sideband

3-18. Which of the followingindividuals is responsible forassigning primary and secondaryLink-11 frequencies before thedeployment of a task force?

1. The aircraft carriercommanding officer

2. The net control stationtrack supervisor

3. The task force commander4. The fleet CinC

3-19. When a Link-11 net isestablished, which of thefollowing sequences ofoperations should be followedto determine readiness of allunits to enter the net?

1. Net Test, Net Sync, rollcall

2. Net Sync, Net Test, rollcall

3. Net Sync, Net Test,Broadcast

4. Roll call, Net Test, NetSync

A. Net SynchronizationB. Net TestC. Roll CallD. BroadcastE. Short BroadcastF. Radio Silence

Figure 3B.

12

IN ANSWERING QUESTIONS 3-20 THROUGH3-25, SELECT FROM FIGURE 3B THEOPERATING MODE DESCRIBED IN THEQUESTION.

3-20.

3-21.

3-22.

3-23.

3-24.

What Link-11 operating modeestablishes a uniform time basefrom which all netcommunications are normallyinitiated?

1. A2. B3. C4. D

In what Link-11 operating modeis each picket unitinterrogated, in turn, by NCS?

1. A2. B3. C4. D

What Link-11 operating modeprovides an overall evaluationof net and equipmentperformance?

1. B2. C3. D4. E

In what Link-11 operating modewill one participating unittransmit data continuously toall other net members?

1. C2. D3. E4. F

In what Link-11 operating modeare the radio set key line anddata terminal audio outputinhibited?

1. C2. D3. E4. F

3-25. In what Link-11 operating modeis a single data transmissionsent only when the operatordepresses the TRANSMIT STARTbutton?

1. B2. C3. D4. E

3-26. Net Sync continuouslybroadcasts which of thefollowing signals?

1. Phase reference frames2. Start codes3. Stop code4. Preamble frames

3-27. When the stored sync mode isoperating, the picket stationuses which of the followingsignals to establish a timebase?

1. An external frequencystandard

2. The internal frequencystandard in the DTS

3. The sync signal receivedfrom NCS

4. The sync signal receivedfrom another picket

3-28. Which of the followingfunctions is NOT tested whenNet Test is running?

1. DTS to radio interface2. CDS computer to DTS

interface3. Radio to antenna interface4. Radio receiver function

3-29. The preamble of a Link-11message consists of a total ofhow many frames?

1. Five2. Six3. Seven4. Eight

3-30. During transmission of thepreamble, the 605-Hz tone istransmitted at which of thefollowing power levels?

1. - 6 d B2. + 6 d B3. -12 dB4. +12 dB

13

3-31. To enable the DTS to detectframe transitions during thepreamble, the 2915-HZ sync toneis phase shifted how manydegrees at each frame?

1. 902. 1803. 2704. 360

3-32. The phase reference frame of aLink-11 header performs whichof the following functions?

1. Provides synchronizationbetween the DTS and the CDScomputer

2. Provides a time referencefor the DTS

3. Provides a time referencefor the radio

4. Provides the reference toextract the data in the nextframe

3-33. During a receive cycle, thestart code causes which of thefollowing actions?

1. The CDS computer to send theprepare to receive datainterrupt

2. The DTS to send the prepareto receive data interrupt

3. The CDS computer to send theprepare to transmit dataexternal function

4. The DTS to send the prepareto transmit data interrupt

3-34. Exactly how many data bits arecontained in each Link-11information frame?

1. 182. 243. 304. 32

3-35. The control stop code isgenerated by which of thefollowing units?

1. NCS only2. Picket station only3. Either NCS or a picket

station, indicating the endof a control message

3-36. During a receive cycle, thestop code (control or picket)causes which of the followingactions?

1. The CDS computer to send theend of data interrupt

2. The DTS to send the end ofdata external function

3. The CDS computer to send theend of receive interrupt

4. The DTS to send the end ofreceive interrupt

3-37. A call-up, or interrogationmessage, consists of a total ofhow many frames?

1. Five2. Six3. Seven4. Eight

3-38. The two frames following acontrol stop code indicatewhich of the following?

1. The address of the NCS2. The next picket address in

the roll call3. The end of the NCS message4. The last address

interrogated

3-39. A picket reply message is sentin which of the followingsequences?

1. Preamble, phase reference,data, stop code

2. Preamble, phase reference,start code, data, controlstop code

3. Preamble, phase reference,start code, data, picketstop code

4. Phase reference, preamble,start code, data, stop code

3-40. The DTS operates in full duplexwhen it performs which of thefollowing operations?

1. System testing2. Net Test3. Normal operations4. Short Broadcast

14

3-41.

3-42.

3-43.

3-44.

3-45.

The DTS performs which of thefollowing functions?

1. Data encryption2. Error detection and

correction3. Track gridlock4. Transmitting data tones on a

carrier frequency

The six hamming bits added tothe data word enables the DTSto correct what maximum numberof data bits?

1. One2. Two3. Three4. Four

The DTS is operating in thedetect and correct mode. Adata word is received by theCDS computer with bit 24=0, andbit 25=1. Which of thefollowing conditions isindicated by this bitcombination?

1. No errors detected2. Parity error(s) detected3. Odd bit error(s) detected,

correction attempted4. Even errors detected, no

correction attempted

The DTS develops a compositesignal consisting of what totalnumber of frequency divisionmultiplexed audio-frequencytones?

1. 22. 113. 164. 30

Bits 4 and 5 of a 30-bit dataword are carried by which ofthe following audio tonefrequencies?

1. 935 Hz2. 1155 Hz3. 1265 Hz4. 1705 Hz

3-46.

3-47.

3-48.

3-49.

3-50.

3-51.

What is the basic unit of theLink-11 transmission?

1. Bit2. Tone3. Frame4. Doppler

In a single frame, the DTS cantolerate what maximum phaseshift error without generatingan error code?

1. + 44 degrees only2. - 44 degrees only3. ± 44 degrees4. ±135 degrees

A phase-shift error of +105degrees in any one of the datatones will cause a single bitto be erroneous.

1. True2. False

Which of the following Link-11signals allows the receivingunit to correct errors causedby the relative motion betweenthe sending and receivingunits?

1. Sync tone2. Doppler tone3. Data carrying tones4. Motion correct tone

During the preamble, the2915-Hz tone sets which of thefollowing references?

1. Frame timing when the DTS isin corrected timing

2. Signal power levels when theDTS is in corrected timing

3. Frame timing when the DTS isin stored timing

4. Signal power levels when theDTS is in stored timing

During the reception of thedata segment of a Link-11message, the 605-Hz Dopplertone should be at which of thefollowing power levels?

1. +12 dB2. + 6 d B3. - 6 d B4. 0 dB

15

3-52. When the DTS is in the OPERATEmode, exactly how many fault-sensing sensors can cause theSUMMARY FAULT lamp to light?

1. 112. 143. 234. 27

3-53. The LAMP TEST switch on theMode Control Panel will causeall of which of the followinglamps to light?

1. Those on the mode controlpanel only

2. Those on the TADIL A controlpanel only

3. Those on the address controlunit only

4. Those on the mode controlpanel, the TADIL A controlpanel, and the addresscontrol unit

3-54. When the FULL-DUPLEX/HALF-DUPLEX switch is in the FULL-DUPLEX POSITION, the transmitsidetone is processed for inputto the computer.

1. True2. False

3-55. When the SIDEBAND SELECT switchis in the DIV position, whichsideband signal is processedfor input to the computer?

1. USB only2. LSB only3. The combination of the USB

and LSB signals4. Either the USB or the LSB,

depending on the signalquality of each sideband

3-56. During normal Link-11operations, the DATA RATEswitch on the mode controlpanel should be in which of thefollowing positions?

1. 1,200 bps2. 2,400 bps3. DUAL 1,200 bps4. TADIL A

3-57.

3-58.

3-59.

3-60.

16

The SYNC MODE switch on themode control panel is used inconjunction with which of thefollowing switches on the TADILA control panel?

1. OPERATE/RADIO SILENCE switch2. NET CONTROL/PICKET switch3. TIMING STORED/CORRECTED

switch4. ERROR CORRECT/LABEL switch

When the SYNC MODE switch isplaced in the FAST position,synchronization is obtained bywhich of the following methods?

1.

2.

3.

4.

Use of the frame timingreference stored during NetSyncUse of the frame timingreference obtained from thepreamble of, the currentmessage onlyUse of the frame timingreference obtained at eachdata frame of the currentmessage onlyUse of both the frame timingreference obtained duringthe preamble and the frametiming of each frame of thecurrent message

The NET BUSY indicator of theTADIL A control panel isactivated by which of thefollowing signals?

1. Signal presence2. Receive mode3. Transmit mode4. Start code detected

The SYNC COMPT indicator islighted after the DTS hasachieved which of the followingconditions?

1. It is in sync with the radio2. It is using stored

synchronization signals3. It is in sync with NCS4. It is testing the internal

sync circuits

3-61. The TIMING/STORED/CORRECTEDswitch is set to the STOREDposition. Which of thefollowing signals will the DTSuse for frame timingsynchronization?

1. The frame timing referencestored during Net Sync

2. The frame timing referenceobtained from the preambleof the current message only

3. The frame timing referenceobtained at each data frameof the current message only

4. Both the frame timingreference obtained duringthe preamble and the frametiming of each frame of thecurrent message

3-62. When the ERROR CORRECT/LABELswitch is in the CORRECTposition, the DTS is capable ofperforming which of thefollowing operations?

1. Detecting and correcting aneven number of bit errors inthe received data word

2. Detecting and correcting anodd number of multiple biterrors in the received dataword

3. Detecting and correcting asingle bit error in eachreceived data word

4. Detecting and correcting asingle bit error in thereceived data message

3-63. When you depress the TRANSMITRESET switch on the TADIL Acontrol panel, it causes theDTS to perform which of thefollowing operations?

1. To immediately stop alltransmissions

2. To inhibit the generation ofoutput data requests,generating a stop code andending the currenttransmission

3. To place the radio in radiosilence

4. To inhibit the generation ofinput data requests,generating a stop code andending the current reception

3-64. The DTS is configured as apicket station in roll callmode. When you depress theTRANSMIT INITIATE switch on theTADIL A control panel, it willcause the DTS to perform whichof the following operations, ifany?

1. To immediately transmit thedata

2. To allow the unit to enterthe net

3. To assume control of the netas NCS

4. None

3-65. On the NCS platform, the MISSCALL indicator on the TADIL Apanel will light when a picketfails to respond to twosuccessive interrogations.

1. True2. False

3-66. The address entered into theOWN STATION ADDRESS switchesperform which of the followingDTS functions?

1. Transmits the enteredaddress to all other membersof the net

2. Transmits the enteredaddress to NCS only

3. Receives messages that matchthe entered address

4. Transmits tactical data whenthe interrogation messageaddress matches the enteredaddress

3-67. On the NCS platform operatingin a Link-11 net where theunits are approximately 100miles apart, which of thefollowing values should beentered into the RANGE IN MILESswitches?

1. 0 miles2. 25 miles3. 50 miles4. 100 miles

17

3-68. With a single address controlindicator, an NCS platform cancontrol what maximum number ofparticipating units?

1. 52. 103. 154. 20

3-69. Data exchange between theLink-11 DTS and the CDScomputer is controlled by theDTS using which of thefollowing control signalprotocols?

1. External interrupts2. External functions3. Input data requests4. Output data requests

3-70. During a receive data cycle,the DTS performs which of thefollowing actions when frametwo of the stop code isdetected?

1. The frame is processed as adata frame and sent to thecomputer

2. The DTS processes the stopcode and resets itself only

3. The DTS sends the end ofreceive external interruptto the computer

4. The computer processes thestop code and closes theinput data buffer

3-71. Which of the following actionsis performed by the DTS when acontrol station stop code isreceived?

1. The DTS compares the nexttwo frames received with theown station address

2. The DTS resets all I/Otiming circuits

3. The DTS sends the next twoframes received to the CDScomputer

4. The DTS sends the prepare totransmit data interrupt tothe computer

3-72. When the DTS recognizes ownstation address, it transmitswhich of the following signalsfirst?

1. Prepare to transmitinterrupt

2. The first frame of thepreamble

3. The phase reference frame4. Input data request

3-73. At the start of a transmitcycle, the output data requestis first set active duringwhich of the following frames?

1. The first frame of thepreamble

2. The first frame of the startcode

3. The phase-reference frame4. The second frame of the

start code

3-74. Which of the following eventstakes place when the CDScomputer does not answer an ODRfrom the DTS within thespecified time limit?

1. The DTS generates the stopcode

2. The DTS hangs-up3. The computer generates an

external function to clearthe DTS

4. The computer sends a stopcode to the DTS

3-75. Which of the following eventsoccur if an interrogated picketstation does not answer aninitial interrogations from theNCS within 15 frame intervals?

1. NCS interrogates the nextstation

2. NCS waits another 15 frameintervals

3. Link-11 network hangs up4. NCS retransmits the

interrogation to the unitthat did not reply

18

ASSIGNMENT 4

Textbook Assignment: “Link-11 System,” chapter 4, pages 4-18 through 4-19(continued); “Link-11 Fault Isolation,” chapter 5, pages 5-1through 5-17.

4-1. A total of how many data tonesare in the composite tonepackage developed by the DTS?

1. 132. 143. 154. 16

4-2. The intelligence (data bits) ina data tone is stored by which

1.

2.

3.

4.

of the following methods?

Phase shifting the tone by apredetermined amount withrespect to the followingframePhase shifting the tone by apredetermined amount withrespect to zero degreesPhase shifting the tone by apredetermined amount withrespect to the precedingframeIncreasing or decreasing theamplitude of the data tonewith respect to thepreceding frame

4-3. During receive operations,exactly how many EDAC bits areextracted from the receiveddata tones?

1. One2. Two3. Five4. Six

4-4. The EDAC bits enable the DTS tocorrect a total of how manyreceived bit errors?

1. One2. Two3. Three4. Four

4-5.

4-6.

4-7.

4-8.

4-9.

When operating the Link-11 witha UHF radio set, you shouldplace the SIDEBAND SELECTswitch in what position only?

1. LSB2. USB3. DIV4. AUTO

With Link-11 transmitting onthe HF range and the sidebandselect switch set to the AUTOposition, which of thefollowing priorities are usedby the DTS to find the dataword with no errors to send tothe computer?

1. LSB, USB, DIV2. LSB, DIV, USB3. DIV, LSB, USB4. DIV, USB, LSB

The Link-11 radio set is in thetransmit mode when the key lineis clear.

1. True2. False

Which of the followingconditions would NOT be a validreason for changing the unitfunctioning as NCS in a Link-11net to improve netcommunications?

1. The current NCS has one PUaddress entered wrong

2. The current NCS has poorreceiver sensitivity and ispolling on top of PUresponses

3. Several PUs are in apropagation shadow

4. Several PUs are out of rangeof the current NCS unit

Changing frequencies willalways solve Link–11 problems.

1. True2. False

19

4-10. When you keep the radio settuned to output maximum power,it causes which of thefollowing problems?

1. Increases RFI/EMI ontransmitting unit only

2. Increases receive dataerrors on receiving units bysaturating the data terminalsets only

3. Increases RFI/EMI on thetransmitting unit andincreases receive dataerrors by DTS saturation

4. Decreases RFI/EMI on thereceiving units

4-11. When the NCS enters dummy PUs,which of the following netconditions will exist, if any?

1. Net efficiency increases2. Net cycle time decreases3. Net cycle time increases4. None, dummy PUs have no

effect on the net

4-12. What following NCS action isthe most effective netmanagement technique when a PUis having trouble maintainingLink-11 communications?

1.

2.

3.

4.

Continuing normal Link-11operations the trouble PUDirecting the PU to go toradio silence so that the PUdoes not respond tointerrogationsDirecting all units tochange from a HF frequencyto an UHF frequencyRemoving the troubled PUfrom the polling sequenceuntil the problem iscorrected and the troubledPU is ready to reenter thenet

4-13. When you set up the DTS to runa single-station POFA, the DTSmust be configured to operatein which of the followingmodes?

1. Simplex2. Half duplex3. Full duplex4. POFA TEST mode

4-14. When you run a single-stationPOFA with the radio set, whichof the following equipmentsis/are NOT checked?

1. Security device 1/0 path2. Antenna coupler3. DTS-to-radio audio lines4. Radio-to-DTS audio lines

4-15. Running a single-station POFAcan assist the technician inisolating a problem in which ofthe following sections of theDTS?

1. Receive timing2. Doppler correction3. DTS to antenna interface4. Transmit timing

4-16. A single-station POFA shouldprint the interrupts in whatsequence?

1. End of receive, prepare totransmit, prepare to receive

2. Prepare to receive, prepareto transmit, end of receive

3. Prepare to transmit, end ofreceive, prepare to receive

4. Prepare to transmit, prepareto receive, end of receive

4-17. A single-station POFA errorprintout that lists bit errorsthat are less than 10 percentof the total words transmittedis considered a successfulPOFA.

1. True2. False

4-18. A single broken line in theswitchboard between the DTS andthe crypto device could causewhich of the followingproblems?

1. One bit always set to alogic “1”

2. One bit always set to alogic “0”

3. All bits randomly set to alogic “1”

4. All bits randomly set to alogic “1” or a logic “0”

20

4-19. The multi-station POFA is runin which of the followingmodes ?

1. Net test2. Roll call3. Broadcast4. Short broadcast

4-20. When a multi-station POFA isrun, what total number of datawords are in each block of datatransmitted?

1. 1152. 2303. 3454. 460

4-21. When a multi-station POFA isrun, all units participating inthe test should be positionedwithin how many miles of eachother?

1. 252. 503. 754. 100

4-22. A multi-station POFA should berun using which of thefollowing frequencies?

1. Any HF frequency2 Any UHF frequency3. The current operational

frequency only4. The current secondary

frequency only

4-23. The multi-station POFA shouldbe run for what minimum amountof time?

1. 5 minutes2. 7 minutes3. 10 minutes4. 15 minutes

4-24. At the completion of the multi-station POFA, the technicianshould record which of thefollowing information on theerror printout?

4-25. A multi-station POFA should beconsidered successful when thelink quality factor is which ofthe following values?

1. Greater than 90 percent2. Greater than 100 percent3. Greater than 95 percent but

less than 100 percent4. It must equal 100 percent

4-26. A multi-station POFA isconsidered successful when thecomputed receive error factoris less than what percentage?

1. 12. 53. 104. 15

4-27. Which of the following buffersis acceptable to be receivedfrom an unrecognized station(UNREC STA) when a multi-station POFA is running?

1. One buffer of 200 words2. One buffer of 230 words3. Two buffers of 200 words4. Two buffers of 230 words

4-28. The heading PARITY STATUS OFCORRECT WORDS lists which ofthe following error conditions?

1. Words determined to becorrect by the DTS paritycheck and found in error bythe computer parity check

2. Words determined to have anerror and corrected by theDTS

3. Words determined to becorrect by both the DTS andthe computer parity checks

4. Words determined to be inerror by the DTS paritycheck and found correct bythe computer parity check

1. Distance and bearing of allPUs

2. Frequency used3. Start and stop time of the

POFA4. All of the above

21

4-29. The LMS-11 is designed toperform which of the followingfunctions?

1. Isolate problems to thecomponent level in theLink-11 system

2. Provide a history of Link-11net performance

3. Provide a real-time visualdisplay of the Link-11 netoperations

4. Provide the technician witha visual display of theLink-11 operation of oneunit

4-30. The LMS-11 is a complex systemdesigned to be permanentlyinstalled.

1. True2. False

4-31. The DPG and CDG equipment casesof the LMS-11 provide isolationfrom which of the followingenvironmental forces?

1. Shock only2. Vibration only3. Shock and vibration4. Power surges

4-32. The LMS-11 system printer ispart of which of the followingequipment groups?

1. Accessory2. Control/display3. Data processing4. Support

4-33. Which of the followingcomponents is NOT part of theLMS-11 data processing group?

1. Control processing unit2. Dual 5.25-inch disk drive

unit3. Audio interface unit4. Power control unit

4-34. The HP9920U computer of theLMS-11 contains what amount ofrandom access memory (RAM)?

1. 2 MB2. 4 MB3. 8 MB4. 12 MB

22

4-35. The data communicationsinterface of the LMS-11provides which of the followingfunctions?

1. Parallel synchronousinterface with the Link-11data terminal

2. Parallel asynchronousinterface with the printer

3. Serial synchronous interfacewith the Link-11 dataterminal

4. Serial asynchronousinterface with the printer

4-36. The audio interface unit of theLMS-11 connects which of thefollowing signals?

1. USB from HF radios only2. LSB from HF radios only3. USB from UHF radios only4. USB and LSB from HF radios

and USB from UHF radios

4-37. To determine the phase shift ofthe Link-11 audio tones, theLMS-11 uses which of thefollowing methods?

1. Fast Fourier Transformformula

2. Comparison of the raw analogsignal with the precedingframe

3. Phase shift signal from theDTS

4. Digital data from the cryptodevice

4-38. The control/display groupconsists of which of thefollowing units?

1. Composite video and coloroutput circuit cardassemblies

2. Data communicationsinterface and HP interfacebus

3. Color monitor and keyboard4. Color printer and

interconnecting cables

4-39. The color display monitor ofthe LMS-11 uses composite videowhen it performs which of thefollowing operations?

1. Normal LMS-11 operations2. Start-up operations only3. Testing operations only4. Both start-up and testing

operations

4-40. The functional keys on the

4-41.

4-42.

4-43.

LMS-11 keyboard are color-codedto facilitate operatorselections and entries.

1. True2. False

During initialization of theLMS-11, which of the followingoperator entries is NOT arequired entry?

1. Date and time2. Own-ship PU number3. Net mode4. Data rate

When initializing the LMS-11,the operator enters 127 framesas the CALL-TIMEOUT value.What type of Link-11 operationis indicated by this entry?

1. NET TEST2. Normal roll call mode3. Satellite link operation4. NET SYNC

The link monitor mode of theLMS-11 displays whatinformation?

1.

2.

3.4.

Quantitative informationconcerning the operation ofa maximum of 21 PUsDetailed characteristics ofthe received signal from aspecified PUReal-time link activityA graphic representation ofthe power levels of thereceived Link-11 tones froma single PU

4-44.

4-45.

Which of the following functionkeys on the LMS-11 keyboardwould the operator depress toselect the link monitor mode?

1. LM2. NET3. SPECT4. PU

A PU address of 77 is used bythe LMS-11 to indicate which ofthe following units, if any?

1. PU 772. NCS3. Task force flagship4. None, 77 is illegal

address

IN ANSWERING QUESTIONS 4-46 THROUGH4-75, REFER TO FIGURE 5-7 IN THE TEXT.

4-46. which of the following colorsindicates the preamble on thelink monitor screen of theLMS-11?

1. Yellow2. Red3. Cyan4. Green

4-47. A small cyan line in the middleof the data field indicates theLMS-11 has detected which ofthe following signals?

1. Start code2. Stop code3. Phase-reference frame4. Noise

4-48. Which of the following displaysis used to indicate the LMS-11is listening?

1. A thick blue line2. A thin blue line3. A thick red line4. A thin red line

23

4-49. The phase-reference frame isdisplayed on the link monitordisplay in what manner?

1. As a small green linebetween the start code andthe data

2. As a small red line betweenthe start code and the data

3. As a small green linebetween the preamble and thestart code

4. As a small red line betweenthe preamble and the startcode

4-50. Data frames are represented on

4-51.

4-52.

the link monitor display bywhich of the following colors?

1. Yellow2. Red3. Cyan4. Green

An NCS report can be easilyidentified on the link monitordisplay by which of thefollowing features?

1. A two digit address at theend of a report only

2. No call-up message betweenthe end of the precedingreport and the NCS reportonly

3. Both a two digit address atthe end of the report andno call up message betweenthe preceding report and theNCS report

4. A call message to the NCSaddress

An address shown in red on theXMT-ADDRS line of the statusdisplay indicates which of thefollowing conditions?

1. The addressed unit is beinginterrogated

2. The addressed unit failed toanswer two interrogations

3. The addressed unit hasreplied to an interrogation

4. The unit indicated is thenext address in the pollingsequence

4-53.

4-54.

4-55.

4-56.

24

When the LMS-11 is operating inthe link monitor mode and aphase reference frame isdetected, which of thefollowing status indicators isactive?

1. CC12. PHA3. PRE4. EOT

When the LMS-11 is operating inthe link monitor mode and thefirst frame of a picket stopcode is detected, which of thefollowing status indicators isactive?

1. CC12. PHA3. PRE4. EOT

In the status box, the numberin the %DATA indicates which ofthe following quantities?

1. The total percentage of datain the last message received

2. The percentage of data thatis error free in the lastmessage received

3. The total percentage of datareceived during the mostrecent net cycle

4. The percentage of data thatis error free receivedduring the most recent netcycle

The net cycle time that isdisplayed in the LMS-11 statusbox indicates which of thefollowing time cycles?

1. Start code to start code ofNCS only

2. Control stop to control stopof NCS only

3. Control stop to control stopof an operator selected PUonly

4. Control stop to control stopfrom either NCS (default) oran operator selected PU

4-57. The Net Display mode of theLMS-11 is capable of displayingtwo separate types ofinformation.

1. True2. False

4-58. In the summarize mode of thenet display, a summary ofquantitative information isdisplayed for a maximum of howmany PUs?

1. 102. 113. 204. 21

4-59. The net display mode can onlybe displayed when Link-11 isoperating in which of thefollowing modes?

1. Net test2. Net sync3. Roll call4. Short broadcast

4-60. The PU field in the header ofthe Net Display screen of theLMS-11 is used to define whichof the following units, if any,while in the summarize mode?

1. NCS2. Own station PU number3. The PU whose recurring

transmission is used todefine a cycle

4. None, the PU field is onlyused during the History mode

4-61. To change the Net Displayscreen from the summarize modeto the PU history mode, theoperator would take which ofthe following actions?

1. Depress the history mode keyon the keyboard

2. Enter a zero into theSUMMARIZE field of the NetDisplay header

3. Enter the PU number of theunit to be monitored in thePU field

4. Both 2 and 3 above

4-62. On the Net Display screen,which of the following valuesindicates an unacceptable SNR?

1. 5 dB2. 15 dB3. 25 dB4. 34 dB

4-63. When the LMS-11 is in the NetDisplay (summarize) mode, whichof the following conditionswill cause the FRAME CNT valueof a picket to be displayed inyellow and followed by a “?”?

1. The average number of framesper transmission exceedsseven

2. The average number of framesper transmission is six orless

3. The average signal to noiselevel per transmissionexceeds 20 dB

4. The average signal to noiselevel per transmission isless than 20 dB

4-64. The %THRU column of the NetDisplay screen displays whichof the following values?

1. The percentage of datareceived by the listed PUthat is error-free

2. The percentage of messagedata frames received by theLMS-11 that contains errors

3. The percentage of messagedata frames received by theLMS-11 that are error-free

4. The percentage of controlcode frames received

4-65. Which of the following powerlevels listed in the REL 605column of the Net Displayscreen indicates normaloperation of the link?

1. -3 dB2. -6 dB3. +3 dB4. +6 dB

25

4-66.

4-67.

4-68.

4-69.

4-70.

Using TADIL A specifications,what is the maximum allowablevariation of power in theLink-11 data tones?

1. 1.0 dB2. 1.5 dB3. 3.0 dB4. 4.0 dB

The PU display of the LMS-11presents a graphicrepresentation of the relativepower and phase error of theLink-11 signal received from aspecified unit.

1. True2. False

What information is displayedon the relative power bar graphof the PU display?

1. The power of the 605-Hz toneonly

2. The relative power of thedata tones with respect tothe 605-Hz tone

3. The relative power of eachdata tone with respect tothe average power of all thedata tones

4. The relative power of eachdata tone with respect to aninternal standard

When the relative power bargraph is read, a data tone thatis +2 dB greater than theaverage will be displayed inwhich of the following colors?

1. Cyan2. Green3. Yellow4. Red

The phase error bar graph ofthe LMS-11 display whatinformation about the Link-11signal?

1.2.

3.

4.

Relative powerMean deviation of the phaseerror onlyStandard deviation of thephase error onlyBoth the mean and standarddeviations of the phaseerror

26

4-71. A standard phase deviation of15 degrees for a data tone willbe represented on the bar graphin which of the followingcolors?

1. Cyan2. Green3. Yellow4. Red

4-72. The LMS-11 will indicate thatthe data received is bad if thestandard deviation falls inwhich of the following ranges?

1. A positive value less than45 degrees

2. A positive value greaterthan 45 degrees

3. A negative value less than45 degrees

4. Both 2 and 3 above

4-73. The incidence of bit errorswill increase as the signal-to-noise ratio increases.

1. True2. False

4-74. Which of the following tonesare graphically displayed bythe LMS-11 Spectrum Display?

1. 30 tones that are the oddharmonics of 55 Hz

2. 30 tones that are the evenharmonics of 55 Hz

3. The 605 Hz tone and thenoise tone only

4. The 15 data tones only

4-75. Under ideal conditions, at whatlevel should the data tones bedisplayed on the bar graph ofthe spectrum display?

1. 0 dB2. +6 dB3. -6 dB4. +4 dB

ASSIGNMENT 5

Textbook Assignment: “Link-11 Fault Isolation,” chapter 5, pages 5-17 through5-19 (continued); “Link-4A,” chapter 6, pages 6-1 through6-6; and “New Technology in Data Communications,” chapter 7,pages 7-1 through 7-6.

5-1. When the operator enters PU 00into the PU address field ofthe spectrum display, whateffect, if any, will it have onthe operation of the LMS-11?

1. 00 is an illegal address;therefore, no data will bedisplayed

2. The LMS-11 will continuouslyupdate the display for eachunit in the net

3. The LMS-11 will update thedisplay for NCS only

4. No effect; the LMS-11 willcontinue to update the lastlegal address entered

5-2. Carrier suppression can only betested when the Link-11 systemis operating in which of thefollowing modes?

1. Net Test2. Net Sync3. Roll call4. Broadcast

5-3. When reading the LMS-11spectrum display, thetechnician notices that onlythe 605-Hz tone and the 2195-Hztones are displayed. Which ofthe following setup entrieswould cause this display?

1. The RESTRICT field set topreamble only

2. The RESTRICT field set todata only

3. The PU field is set to aunit not in the net

4. The SIDEBAND SELECT is setto USB only

5-4. The CDS computer outputs serialdigital data to the Link-14ADTS.

1. True2. False

5-5. Link-4A is used to transmitwhich of the following types ofinformation?

1.

2.

3.

4.

High-speed computer-to-computer tacticalinformationTactical information from aCDS ship to a non-CDS shipAircraft control and targetinformationAll of the above

5-6. Link-4A data is transmitted byusing which of the followingmethods?

1. Frequency-shift keying2. Phase-shift keying3. Audio frequency tone shift4. Quadrature differential

phase-shift keying

5-7. What is the maximum number ofaircraft that can be controlledby a single Link-4A controllingstation?

1. 252. 503. 754. 100

5-8. Aircraft control messages fromthe Link-4A controlling stationare developed by the CDScomputer using which of thefollowing types of information?

1. Radar-derived target data2. Reply data from aircraft3. Other sources of tactical

information4. All of the above

5-9. Link-4A uses which of thefollowing frequency bands fordata exchange?

1. HF only2. UHF only3. VHF only4. Both UHF and VHF

27

In which of the following5-10.

5-11.

5-12.

5-13.

5-14.

Link-4A modes of operation isan aircraft directed to aspecific location to be at anoptimum position for an attack?

1. Precision course direction2. Automatic carrier landing

system3. Air traffic control4. Intercept vectoring

In which of the followingLink-4A modes of operation isused to maintain safe flightpatterns and assigns priorityfor landing approach?

1. Precision course direction2. Automatic carrier landing

system3. Air traffic control4. Intercept vectoring

Which of the following Link-4Amodes of operation is used forthe remote guidance of bombers,reconnaissance aircraft, anddrones?

1.2.

3.4.

Precision course directionAutomatic carrier landingsystemAir traffic controlIntercept vectoring

In which of the followingLink-4A modes of operation isused to land an aircraft on theflight deck of a carrier?

1. Precision course direction2. Automatic carrier landing

system3. Air traffic control4. Intercept vectoring

The CAINS aircraft alignmentdata loaded into the navigationcomputer of the aircraftconsists of which of thefollowing types of data?

1. The latitude and longitudeof the ship only

2. The ship’s velocity only3. The latitude, longitude, and

ship’s velocity4. The waypoint data

5-15.

5-16.

5-17.

5-18.

5-19.

5-20.

The CAINS alignment andwaypoint data is initiallyloaded into the aircraft usingwhich of the following methods?

1. Hard-wired deck edge outletboxes only

2. UHF RF transmission only3. Either hard-wired deck edge

outlet boxes or UHF RFtransmission

4. HF transmission only

The standard CDS controlmessage is (a)

(2), (14)milliseconds in duration, whilethe reply message is (b)

(14), (18)milliseconds in duration.

1. (a) 2 (b) 142. (a) 2 (b) 183. (a) 14 (b) 144. (a) 14 (b) 18

The CAINS receive cycleduration is equal to what totalnumber of milliseconds?

1. 22. 43. 144. 18

The transmit frame is dividedinto what total number of 200µsec time slots?

1. 132. 563. 704. 200

What total number of time slotsmake up the sync preamble ofeach transmit frame?

1. 132. 423. 564. 70

What total number of transmitframe time slots containmessage data bits?

1. 82. 133. 564. 70

28

5-21. Which of the following transitframe signals causes thetransmitter to turn off andstarts the receive cycle?

1. Stop pulse2. Sync burst3. Guard interval4. Transmitter un-key

5-22. The reply message contains whattotal number of data timeslots?

1. 132. 423. 564. 70

5-23. Which of the following Link-4Atest messages is used toprovide aircraft with the meansto verify proper operation ofLink-4A?

1. The monitor reply message2. The monitor control message3. The universal test message4. All of the above

5-24. Which of the following Link-4Atest messages causes internaltesting of the data terminalset?

1. The monitor reply message2. The monitor control message3. The universal message4. All of the above

5-25. Which of the followingAN/SSW-1() subassembliesprovides system timing forLink-4A operations?

1. Digital-to-digital converter2. Monitor test panel3. Coordinate data transfer

control4. Pulse amplifiers

5-26. Which of the following piecesof equipment is replacing olderLink-11 data terminal sets?

1. AN/USQ-36 Data Terminal Set2. C2P3. AN/USQ-125 Data Terminal Set4. Link-16

5-27. The CP-2205 (P) (V)/USQ-125processor board performs whichof the following functions?

1. Modulation/demodulation2. Error detection and

correction3. Radio set interface4. All of the above

5-28. Which of the followingCP-2205 (P) (V)/USQ-125components provides forcommunications with the CDScomputer?

1. Processor board2. Interface board3. Power supply4. Modulator

5-29. The CP-2205 (P) (V)/USQ-125 iscapable of data encrytion.

1. True2. False

5-30. The single-tone waveform linkcapability of the CP-2205 (P)(V)/USQ-125 provides which ofthe following functions?

1. Interface with a satellitemodem

2. Increases UHF transmissionrange

3. Increases HF transmissionrange

4. Reduces HF propagationanomalies

5-31. Which of the following optionsof the CP-2205 (P) (V)/USQ-125incorporates a routine tocalculate the optimumfrequency?

1. Enhanced link qualityanalysis

2. Maximum useable frequency3. Single-tone waveform link4. Multi-frequency link

5-32. Which of the following optionsof the CP-2205 (P) (V)/USQ-125transmits Link-11 data througha standard wire-line modem?

1. Enhanced link qualityanalysis

2. Maximum useable frequency3. Single-tone waveform link4. Multi-frequency link

29

5-33. Which of the following optionsof the CP-2205 (P) (V)/USQ-125incorporates most of thefunctions of the LMS-11?

1. Enhanced link qualityanalysis

2. Maximum useable frequency3. Single-tone waveform link4. Multi-frequency link

5-34. Which of the following optionsof the CP-2205 (P) (V)/USQ-125improves Link-11 operations byusing four frequenciessimultaneously?

1. Enhanced link qualityanalysis

2. Maximum useable frequency3. Single-tone waveform link4. Multi-frequency link

5-35. The normal configuration of themulti-frequency link optionsuses (a)

(2) (3)HF frequencies and (b)

(1), (2)UHF frequencies.

1. (a) 2 (b) 12. (a) 3 (b) 13. (a) 2 (b) 24. (a) 3 (b) 2

A. Radio echo testB. Loopback test 1C. Loopback test 2D. Loopback test 3E. Loopback test 4F. DTS fault isolation test

FIGURE 4A.

30

IN ANSWERING QUESTIONS 5-36 THROUGH5-40, SELECT FROM FIGURE 4A THE SYSTEMTEST OPTIONS OF THE CP-2205(P) (V)/USQ-125 DATA TERMINAL SET DESCRIBED IN THEQUESTION NOT ALL ITEMS IN THE LISTARE USED.

5-36.

5-37.

5-38.

5-39.

5-40.

This option is selected when asingle station POFA is runningwithout the radio.

1. A2. B3. C4. D

When this test is run, thecomputer interface is disabledand a test message isrepeatedly sent to the radioset.

1. A2. B3. C4. D

This test is used to verify theoperation of the computerinterface, crypto device, andthe data terminal interfacecircuits.

1. C2. D3. E4. F

This test places the DTS infull-duplex mode to run asingle station POFA with theradio.

1. A2. B3. C4. D

This option performs aninternal self-test of the DTSaudio circuits.

1. A2. B3. C4. D

5-41. The data terminal can becontrolled from a remotelocation by use of which of thefollowing pieces of equipment?

1. A 286 personal computer only2. A 386 or better personal

computer only3. The C-12428/USQ-125 Control

Unit only4. Either a 386 or better

personal computer, or theC-12428/USQ-125 Control Unit

5-42. Link-16 uses which of thefollowing communicationsprotocols?

1. Netted or roll call2. Time division, command and

response3. Time division multiple

access4. Frequency-division

multiplexing

5-43. Each unit participating in aLink-16 net is identified byassigning each unit what typeof designator?

1. A PU number2. A JU number3. A link identifier4. A hull number

5-44. What is the duration of eachtime slot in a Link-16 message?

1. 7.8125 msec2. 7.8125 µsec3. 7.8125 seconds4. It varies, according to the

amount of data transmitted

5-45. During the transmission ofdata, exactly how often doesLink-16 change frequency?

1. Every 13 µsec2. Every 13 msec3. Daily4. When the frequency is

excessively noisy

5-46. Link-16 is configured for astacked net. At-any one time,what number of nets can a

5-47.

5-48.

5-49.

5-50.

single terminal transmit andreceive data?

1. One2. Two3. Three4. Four

A Link-16 data word iscomprised of what number ofdata bits?

1. 502. 603. 704. 80

A Link-16 fixed format messageis which of the followingmessage types?

1. V-series2. R-series3. M-series4. J-series

Which of the following messagetypes are used for Link-16voice communications?

1. Fixed format2. Free text3. Variable format4. Unformatted

Which of the following messagetypes are used to exchangetactical data?

1. Fixed format2. Free text3. Variable format4. Unformatted

31

ASSIGNMENT 6

Textbook Assignment: “New Technology in Data Communications,” chapter 7, pages7-6 through 7-11 (continued); “Local-Area Networks,” chapter8, pages 8-1 through 8-14.

6-1.

6-2.

6-3.

6-4.

6-5.

Compared to Link-11, Link-16 isnodeless for which of thefollowing reasons?

1. Once the net is established,all units must participate

2. Only one unit controls thenet

3. Once the net is established,operations can continueregardless of theparticipation of anyparticular unit

4. A computer is not requiredto participate in the net

Which of the following JTIDSsecurity features is designedto prevent jamming?

1. Data encryption2. Waveform encryption3. Introduction of jitter and

noise4. Frequency hopping

Which of the following networkparticipation groups isnormally excluded from Navycommand and control units?

1. Weapons coordination2 Air control3 Fight-to-fighter4 Secure voice

JU numbers 00001 through 00177are normally assigned to whichof the following units?

1. Link-4A and Link-16 capableunits

2. Command and Control units3. Link-16 capable aircraft4. Link-11 and Link-16 capable

units

Which of the following Link-16track numbers would designatethe same Link-11 track?

1. 00000 through 077772. 01000 through 777773. 00200 through 077774. 00500 through 77777

32

6-6.

6-7.

6-8.

6-9.

A Link-16 track that has areported track quality of 15indicates the track is withinexactly how many feet of thereported position?

1. 102. 253. 504. 75

Which of the following trackidentifications has been addedfor use with the Link-16system?

1. Neutral2. Hostile3. Assumed hostile4. Unknown

The identifier “Unknown assumedenemy has been changed in theLink-16 system to whatidentifier?

1. Neutral2. Suspect3. Unknown assumed hostile4. Hostile

Link-16 has added which of thefollowing data fields tofriendly aircraft statusreports?

1. Ordnance inventory2. Equipment Status3. Fuel available for transfer4. All of the above

6-10. The Relative Navigationfunction of the Link-16 systemis required for which of thefollowing functions?

1. Maintain synchronization2. Maintain position3. Detect course errors4. Correct the navigation plot

6-11.

6-12.

6-13.

Which of the followingequipment configurations fullyimplements the capabilities ofthe Link-16 system?

1. Model-32. Model-43. Model-54. Model-6

Using the Link-16 Model-5system, link data generated bythe ACDS computer is normalizedto be independent of anyparticular system.

1. True2. False

Using the Link-16 Model-5system, which of the followingcomponents formats link datafor transmission over any oneof the three data links?

1. ACDS2. C2P3. Link-16 data terminal4. TDS computer

A. Digital data processor groupB. Receiver/transmitter groupC. High power amplifier groupD. Power interface unitE. Secure data unit

Figure 6A.

IN ANSWERING QUESTIONS 6-14 THROUGH6-17, SELECT FROM FIGURE 6A THEEQUIPMENT COMPONENT GROUP OF THE JTIDSTERMINAL THAT PERFORMS THE FUNCTION OROPERATION DESCRIBED IN THE QUESTION.NOT ALL ITEMS IN THE LIST ARE USED.

6-14. A removable assembly thatstores cryptovariables.

1. B2. C3. D4. E

6-15. Generates a 75-MHz intermediatefrequency for internalcommunications.

1. A2. B3. C4. D

6-16.

6-17.

6-18.

6-19.

6-20.

6-21.

Provides the interface with theantenna.

1. A2. B3. C4. D

Performs digital-to-analog andanalog-to-digital conversion ofvoice signals.

1. A2. B3. C4. D

The Command and Control (C2P)system controls and manages theinterface of which of thefollowing data links?

1. Link-4A only2. Link-11 only3. Link-16 only4. All tactical data links

Messages received by the C2Pover the Link-11 net cannot beretransmitted over the Link-16net.

1. True2. False

A local area network (LAN)performs which of the followingfunctions?

1. Enables users to share data2. Enables users to share

peripheral devices3. Allows users to send and

receive messages viacomputer

4. All of the above

Which of the following items isa node in a LAN system?

1.2.3.4.

Twisted pair cableCommunications mediaFiber-optic cableLarge capacity hard drive

33

6-22. Twisted pair cable used in aLAN has which of the followingadvantages?

1. High data transmissionspeeds

2. Low costs and easy toinstall

3. Shielded from electricalinterference

4. Secure data transmission

6-23. In designing a LAN system thatrequires the transmission ofdigital data, audio, and videosimultaneously, which of thefollowing cables would be bestsuited to the system?

1. Twisted pair2. Shielded twisted pair3. Broadband coaxial4. Baseband coaxial

6-24. Which of the following types ofcable is immune to interferencefrom electrical and electronicdevices?

1. Fiber optic2. Baseband coaxial3. Shielded twisted pair4. Telephone cable

6-25. Which of the following devicesprovides the interface betweenthe LAN and a personalcomputer?

1. Network server2. NIC3. Disk server4. Cables

6-26. Which of the following devicesis used to manage the sharedresources of the LAN?

1. Network server2. NIC3. Disk server4. Network monitor

6-27. Early disk servers sufferedfrom which of the followingproblems?

1. Lack of security2. No data organization3. No disk management4. All of the above

6-28.

6-29.

6-30.

6-31.

6-32.

34

Ensuring data integrity bypreventing multiple usersaccess to the same record atthe same time is known as whatprocess?

1. File locking2. Field locking3. Record locking4. Disk lockout

Which of the following serverswas developed to providereliable disk management in aLAN?

1. Disk server2. Print server3. File server4. Network server

Which of the followingfunctions is NOT performed bythe file server?

1. Routing files to a centralprinter for printing

2. Processing of the networkcontrol software

3. Converting high-level diskscalls from a workstation tolow-level disk commands

4. Maintaining the list of userprivileges andauthorizations

When designing and building aLAN system, all workstationsmust be from the samemanufacturer.

1. True2. False

The OSI reference model is usedto define which of thefollowing communicationsstandards?

1.

2.3.4.

Interconnection ofcommunications facilitiesSoftwareHardwareProtocol

6-33. What layer of the OSI referencemodel describes the electrical,the mechanical, and thefunctional interface of thecommunications channel?

1. Physical layer2. Data link layer3. Network layer4. Transport layer

6-34. What layer of the OSI referencemodel establishes and deleteshost-to-host connections acrossthe network?

1. Data link layer2. Network layer3. Transport layer4. Session layer

6-35. As a translator for thenetwork, what layer of the OSIreference model provides acommon representation for datawhich can be used between theapplication processes?

1. Network layer2. Transport layer3. Session layer4. Presentation level/layer

6-36. Which of the following layersof the OSI reference modelprovides error-freetransmission of informationover the physical medium?

1. Physical2. Data link3. Network4. Transport

6-37. Communications between users ontwo different machines areestablished by what layer ofthe OSI reference model?

1. Data link2. Network3. Transport4. Session

6-38. Based on network conditions andpriority of service, what layerof the OSI reference modeldecides which physical pathwaythe data should take?

1. Physical2. Data link3. Network4. Transport

6-39. The application level/layer ofthe OSI reference modelprovides the protocols forwhich of the following useritems?

1. Media interface2. Electronic mail3. Routing of messages between

networks4. Data compression

6-40. Which of the following is NOT aLAN topology?

1. Linear2. Ring3. Star4. EtherNet

6-41. Which of the following featuresof a linear bus topology shouldbe considered an advantage?

1. Signal interference whennodes are too close to eachother

2. System remains operable evenwhen one or more nodes fail

3. Very secure system4. Very easy to run system

diagnostics from the LANadministrator

6-42. In which of the followingnetwork topologies, if any, iseach node individuallyconnected to the networkserver?

1. Linear bus2. Star3. Ring4. None of the above

35

6-43. Which of the following networkaccess methods requires eachnode to wait for permission totransmit data?

1. CSMA2. CSMA/CD3. Token passing4. Contention

6-44. On a network that uses theCSMA/CD access method, which ofthe following actions, if any,will be taken when a datacollision is detected?

1.

2.

3.

4.

The workstation will ceasetransmission and wait untilthe line is clearThe workstation willcontinue to transmit dataThe network server willassign the next open time tothe workstation thatsuffered the collisionNo action is taken; the datais lost

6-45. In a LAN using a token ring—topology, the interface andprotocols are defined by whichof the following IEEEstandards?

1. IEEE 8022. IEEE 802.33. IEEE 802.44. IEEE 802.5

6-46. Which of the following LANsystems uses a token ringtopology and has a datathroughput of 4 Mbits and 16Mbits per second?

1. EtherNet2. STARLAN3. ARCnet4. IBM Token Ring

A. Control kernelB. Network interfacesC. File systemsD. File extensions

Figure 6B.

IN ANSWERING QUESTIONS 6-46 THROUGH6-49, SELECT FROM FIGURE 6B THENETWORK OPERATING SYSTEM COMPONENTTHAT PERFORMS THE FUNCTION DESCRIBEDIN THE QUESTION. NOT ALL ITEMS IN THELIST ARE USED.

6-47. Provides low-level subnetprotocols and translation forbridging hardware drivers withthe network operating system.

1. A2. B3. C4. D

6-48. Controls data organization,storage, and retrieval on thevarious storage systemsavailable to the network.

1. A2. B3. C4. D

6-49. The main subsystem of thenetwork operating software.

1. A2. B3. C4. D

6-50. Which of the following networkoperating systems, if any, isdesigned for very few users andlight usage?

1. Full featured2. Low cost3. Zero slot4. None of the above

36