Broadcast Engineering. - americanradiohistory.com · 2019-07-17 · DECEMBER, 1971175 cents...

DECEMBER, 1971175 cents

Broadcast Engineering.the technical journal of the broadcast-communications industry ~A HOWARD w. SAMS PUBLICATION

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FCC Explains NewTV Remote ControlRules

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December, 1971 •Volume 13, No. 12

'Broadcast Engineering EDITORIALGEO. H. SEFEROVICH, DirectorRONALD N. MERREL, EditorCARL BABCOKE, Technical

MORRIS COURTRIGHT, AutomationPAT FINNEGAN, MaintenanceHOWARD T. HEAD, FCC RulesROBERT A. JONES, FacilitiesWALTER JUNG, Solid State

ANDRA BOYLE. Editorial AssistantH. G. ROESLER, CartoonistDUDLEY ROSE, Art Director

LEO G. SANDS, CATV

The technical journal of the broadcast-communications industry

EDITORIALADVISORYBOARDLES NELSON, Chairman

Howard W. Sams & Co., Indianapolis

CIRCULATIONEVELYN ROGERS, Manager

ADVERTISINGE. P. LANGAN, Director

R. JACK HANCOCK, ManagerJOAN HIRES, ProductionJAKE STOCKWELL, Sales

20 The New Remote Control VIT Signal. An FCC Rules andStandards Division Engineer explains the TY remote control/monitoring rules in an exclusive BE article. Bruce Longfellow.

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48 Digital Logic Basics. Part three of a four-part series explaining logic basics and descriptions of what part they play inBroadcast circuits. E. Stanley Busby, Jr.

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ABOUT THE COYERThe cover this month depictthe theme of an FCC articleon the new remote controlrules. The article begins onpage 20 . An official and exelusive report on interpretingthe new rules. Further coverage included in NAEB coverage in the Industry Newssection.

BROADCAST ENGINEERING is publishedmonthly by lntertec Publishing Corp., 1014Wyandotte Street. Kansas City, Missouri64105. Telephone, 913/888-4664.

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DEPARTMENTSBROADCASTENGINEERINGis mailed free toqualified persons engaged in commercial andeducational radio and television broadcasting.Non-qualified subscriptions in the U.S. are$6.00 one year, $10.00 two years, $13.00 threeyears. Outside the USA add $1.00 per year tocover postage. Single copy rate 75 cents. Backissue rate $1.00. Adjustments necessitated bysubscription termination at single copy rate.

Controlled Circulation postage paid at Indianapolis, Indiana.

Direct Current.. . 4Letters to the Editor. 8Industry News. . 11CATV Scope 16Engineers Exchange. . .. 56Tech Data..... . . . . . .. 59Ad Index 60

I~ Robert E. Hertel, Publisher

Copyright. 1971. Howard W. Sams & Co.. Inc. All Rights Reserved, Material may not be reproduced orphotocopied in any form without written permission of publisher.

2

lntertec Publishing Corp.Subsidiary of Howard W. Sams & Co., Ine.

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4

DIRECT CURRENTFROM D. C.December, 1971

Howard T. Head

Translators vs. CATV?The Commission has rejected a protest by a CATV system in Colorado against a grant of fivetelevision translators to cover the community served by the cable system. The CATVoperator had alleged that the translators would provide economic competition against thecable system.

The Commission noted that the available information indicated that both the CATV systemand the translators would provide their own types of service. Cable subscribers would beable to obtain signals not delivered by the translators, and would serve areas wheretranslator reception was inadequate. The translators, on the other hand, would provide TVservice to areas beyond the reach of the CATV cables.

In another action, however, the Commission rejected a proposal by a UHF TV station inMassachusetts to operate a translator in the same city as the TV station to be programmedby "distant signals" from outside TV broadcast stations. One of the principal reasons citedin rejecting the proposal was the Commission's ban on overlapping signals under commonownership. Whether a different result would have been reached otherwise remains a goodquestion.

EBS Closed Circuit Tests Suspended IndefinitelyThe provisions of the Emergency Broadcast System (EBS) for random closed circuit testshave been suspended by the Commission until further notice. This suspension follows theconfusion created by the closed circuit test of September 14, 1971 (See last month's DCcolumn) which disclosed "a large number of additional deficiencies.

The Commission action is the most recent in a series of events pointing up the problemswhich have been encountered in the emergency notification system. Meanwhile, the Officeof Civil Defense (OCD) continues with the planning of its Decision Information DistributionSystem (DIDS) which will employ a network of high power LF and VLF stations totransmit alerting and other warnings.

The White House Office of Telecommunications Policy (OTP) continues to keep theproblem under close scrutiny.

(Continued on page 6)

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(Continued from page 4)

AM Freeze Nearing An End?The Commission has accepted an application for a fulltime AM station in Iowa,notwithstanding the provisions of the current "freeze" on acceptance of new applications.During the freeze, the Commission has accepted only a handful of such applications, each ofwhich has been characterized by the almost complete absence of other AM service.The acceptance of the Iowa application is unusual for two reasons. First, the proposedstation would be the second AM station in the city. The other station operates as anon-commercial educational station. Second, the rural surrounding area is served at night byonly a clear-channel station 90 miles distant. However, the applicant argued that theCommission should not consider the distant clear channel signal to constitute primaryservice at night, an argument frequently made in the past but uniformly rejected.

The Commission continues to plod along toward new AM rules that would end the freeze. Apresent target of new rules could be a Christmas "package". Unless new rules are adopted,exceptions of the type involved in the Iowa case are certain to become more and morefrequent.

Cable Origination Channel Identification ProposedThe Commission has proposed that CATV systems be required to use standard identificationof all programs originated by the system. The identification required would be "cable TV,Channel __ , (location).''

The proposal was made for two reasons. There have been complaints by cable viewers thatsome cable systems use call signs with their original programs which are sufficiently similarto TV broadcast calls to create confusion. Further, the Commission points out that thereservoir of remaining "K" and "W" call signs is becoming more and more limited. Also, theFCC's Field Engineering Bureau continues to receive complaints of interference to off-airTV reception caused by leakage and radiation from CATV systems. Most of thesecomplaints appear to be associated with the use by cable systems of channels for localorigination which could not be used for local broadcast carriage because of on-channelghosting resultinq from high ambient radiated signals.

Short CircuitsThe Commission has proposed a substancial increase in the required minimum operatingschedule of FM broadcast stations, who may now broadcast as little as 36 hours perweek ... The Commission approved the use of 72-76 MHz band for the control of all typesof models, on a shared basis with other services... The FCC has approved the continued useof the 4 GHz and 6 GHz bands for Community Antenna Relay Systems (CARS) underspecial circumstances.




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lETTERS V@ voo~~mmAutomatic Leveling System

Dear Editor:Let me extend thanks and com

pliment Broadcast Engineering forpublishing the excellent and timelyarticle on "Preventing FM Overmodulation", by W. J. Kabrick, inthe September 1971 issue.

Having a very long engineeringbackground in FM broadcasting,I certainly appreciate the value ofMr. Kabrick's analysis of the problem. and particularly his suggestions for solution.

KIKK-FM since 1968 has madeuse of an automatic leveling systemconsisting of a modern fast attacktime conventional limiter followedby the selective peak clipping "TopLevel" system as suggested byMr. Kabrick.The latter device does require

knowledgeable calibration andcompetent regular supervision tosee that accurate calibration ismaintained. Other than that, however, it performs admirably in allowing a relatively high averagemodulation level. The Kl KK-FMprogram material does not requirea wide dynamic range.

The total main channel maximummodulation limit is 80 percent dueto stereo and SCA service. Suchclipping as occurs in the Top Levelsystem at Kl KK-FM does not result in any discernable distortionnor does it produce any audiblecrosstalk into the SCA service.Random excessively fast and highamplitude peaks do overshoot thedeviation limit occasionally but theduration is so short and the energycontent so low they pose no realproblem. I feel it is a pretty fairsolution to the FM overmodulationproblem.

I have mixed emotions about Mr.Kabrick's suggestion that the longtime solution to the FM overrnodulation problem is to dispense withthe standard pre-emphasis/deemphasis bit. I grant that this requirement does cause some problems. On the other hand it gives

a IO dB noise advantage to the FMbroadcast system main channel.And I am not at all sure the industrycan afford to give it up.

Gerald R. ChinskiDirector, EngineeringKIKK/KIKK-FMHouston, Tex.

Exciter IdentificationHelp Needed

Dear Editor:Below is a photograph of an

FM exciter that was given to usthat we are trying to identify.

The unit measures 19" X 15\lí",has no identifying marks, serialnumbers, or trade names. The output tube is a 5686. It has provisionsfor stereo.

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The unit is well built with qualitycomponents and cleanly laid out.

If anyone could help us to identify the manufacturer and/or obtainschematics, we will be very grateful.

Mark C. WorleyTransmitter SupervisorKAM U-TVCollege Station, Tex.

On Using A Diode ForTransient Suppression

Dear Editor:The letter to the Editor in the

September issue concerning theuse of a diode as a transient suppressor appears in error due to thefact that it is not the zener break-

(Contmued 011 )




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down of the diode that limits thetransient voltage.

Since an inductor will tend tooppose any change in current, thetransient current will be of thesame polarity as the operatingcurrent, but the transient voltagewill be of opposite polarity. Thiscondition will then forward biasthe diode and short the transientvoltage.

Michael J. SimmonsMaintenance SupervisorWMFE-TVOrlando, Fla.

Editor's Note: We expected abigger reaction to the original letterthan we actually got. For thisreason, in the Engineer's Exchangecolumn you will find a detailedexplanation of how the diode worksas a transient suppressor. 1n fact,during the coming year we will berunning a series of articles explaining the theory and use of severalsolid state devices.

For further information, we suggest you pull some of your copiesof 1971 Broadcast Engineering andnote the books listed in our BookReview columns. One we thoughtwas particularly good: WorkshopIn Solid State, by Harold E. Ennes.This book should be on the bookshelf of every station. It is available through Howard W. Sams &Company, 1ndianapolis, Ind. 46206.Ind. 46206.To clarify another matter - as a

matter of fairness to several authors- telco remotes cannot be coveredin one general article. The reportsprinted in this magazine have comefrom stations working through several different telephone companies.Therefore, the specifics in eachcase may be different from whatexists in your area. We suggestyou show these articles and exchange items to your telco contact.It might make a difference.

\\l Ir (U)ULD~ LiJ'E Tf'/S,"




Microwave Rules ChangeParts 2 and 21 of the Rules for

licensing of common carrier microwave radio station to relay TVsignals to cable TV systems havebeen modified by the FCC (Docket15586). as of November 30.The changes will allow limited

use of the 4 and 6 GHz commoncarrier bands for the purpose ofserving cable TV systems and toeliminate the conditional renewalof these facilities.

Under previous rules, with someexceptions, microwave facilitiesfor transmission of TV signals tocable systems were limited to the11 GHz band. Applications for newcommon carrier microwave facilities in the 4 GHz and 6 GHzbands to serve cable TV systemswere not accepted and existingfacilities could be renewed, afterFebruary I, 1971. only under certain conditions.

The Commission said that useof 11 GHz frequencies would haveno substantial adverse economicor other consequences on carriersprimarily serving CATV systems.It pointed out also that, in viewof the congestion in the lowerbands and the heavy spectrumimpact of cable TV service, thelimitation is "reasonable" to meetthe growing demand for terrestrialand satellite general communications.

The Commission said, however,it believed that some relief wouldbe appropriate and that it wouldmaintain the prohibition against theauthorizations for new frequencypaths in the 4 and 6 GHz bandsto serve cable TV systems butwould continue the policy of considering waiver requests under itsFebruary 3, 1970 MemorandumOpinion and Order (21 FCC 2d284), and would eliminate the conditions on renewals of licensesgranted after February I, 1971. Itsaid this is a "reasonable compromise," since the lower frequencies will be reserved in areas

December, 1971

of greatest congestion, while waivers will permit cable TV use inareas where congestion is not aproblem.

A carrier, which has been authorized to operate on a lower frequency for cable purposes, wouldnot be subject to the uncertaintyand financial risk entailed in anauthorization which would be subject to pre-emption, the Commission pointed out.

Stations which supply cable service on the lower frequencies andwhich are located within 50 milesof one of the top 25 metropolitanareas are few in number and theyhave been made eligible for renewal, the Commission said. However, no waivers for new or additional 4 and 6 GHz facilities willbe granted in these restricted zoneswithout a showing of compellingand unusual circumstances.

The rule changes, which deleteFootnote NG55 in Section 2.106and amend Section 21.70 I(i). became effective November 30, 1971.

Action by the Commission October 14, 1971, by MemorandumOpinion and Order. Commissioners Burch (Chairman), Bartley,Robert E. Lee, H. Rex Lee andWells with Commissioner Johnsonconcurring in the result; Commissioner Reid not participating.

Commission WantsEquipment Form Change

The Commission has specifiedFCC Form 723 for use by applicants for type acceptance of equipment. Use of this form is encouraged although, at the present time,its use is optional. Future amendment of the rules is planned to require that this form be submittedwith type acceptance applications.A separate copy of Form 723should be submitted for each equipment type number.

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12

450-470 MHz Band

Mobile Requirements RelaxedParts 89, 91, 93 and 95 of the

rules have been amended by theCommission to relax technical requirements for authorization andoperation of control stations inmobile relay systems using frequencies in the 450-470 MHz band(Docket 18740). (Control stationspermit communications from afixed location to mobile units.)

The amendments permit the use,in certain situations, of bi-directional, cardioid, or omnidirectionalantennas; allow certain requiredsignal measurements to be made atone location, in cases in which afixed station is used to controlmore than one mobile relay station; and permit an applicant to"certify" that the "output power ofthe proposed station transmitterwill be adjusted to comply withthe . . . signal level limitation."Licensees will also be required tomaintain records of the necessarymeasurement data. Additionally,control stations will be allowed tooperate with a frequency toleranceof -+- .0005 percent, instead of thepresent tolerance (±0.00025). Thetighter tolerance, however, is to beretained for all other fixed stationsoperating in this band.

In its Notice of Proposed RuleMaking issued November 24, 1969,(34 F.R. 19034) the Commissionalso proposed to eliminate the requirement for coordination forcontrol stations. The Commissionsaid that the commenting partiesopposed this, arguing, among otherthings, that in view of the proposalto relax regulations governing theuse of directional antennas, therewas "more reason than ever torequire coordination; and overall,they conclude, the requirementmakes possible the use of moreeffective and efficient assignmenttechniques." Its objective, the Commission noted, was to eliminate arequirement it felt was unnecessary,and lessen the burden on applicantsfor control station facilities in thisclass. Upon review of the comments, however, the Commissionstated it would retain the coordin-

ation requirement, at least for thepresent.

The proposed amendments became effective November 8, 1971.This action terminates the proceeding.

Industrial RadioAffected By LatestRules Amendment

Amendment of Parts 2, 21, 89,and 91 of the Rules with regardto the allocation of frequencies inthe bands 35.19-35.69 and 43.19-43.69 MHz has been proposed in arulemaking notice by the FCC. Theproposal involves channel splittingof the two bands to allow for moreassignable frequencies.The action was in response to a

petition by the Special IndustrialRadio Service Association (SIRSA)requesting the Commission to reallocate to the Special Industrial Radio Service certain frequencies inthe bands 35.2-35.68 MHz and43.2-43.68 MHz presently allocatedto the Domestic Public Land Mobile Radio Service for use by wireline common carriers.

The petition was opposed byPacific Northwest Bell TelephoneCompany; American Telephone andTelegraph Company; Michigan BellTelephone Company; Pacific Telephone and Telegraph Company;United States Independent Tele-




phone Association; Ohio BellTelephone Company; and NewYork Telephone Company.

SIRSA contended that the channels were being used very lightlyby the wirelinc carriers while Special Industrial frequencies in thesame general portion of the spectrum were becoming overcrowded,and concluded that its proposalwould increase the utilization ofthese bands and that the same timehelp to relieve growing congestionin the Special Industrial Service.It requested that the separation between assignable frequencies inthese bands be reduced from 40kHz to 20 kHz in line with otherland mobile operations in this sameregion of the spectrum.

Pointing out that the technicalstandards contained in the rulesspecify a maximum authorizedbandwidth of 20 kHz for this rangeof the spectrum, the Commissionproposed to split-channel the bands35.2-35.68 MHz and 43.2-43.68MHz which would provide 46 assignable frequencies. The centerfrequencies of the existing channelswould be retained for assignmentand the 10 kHz splinters at eachencl of the bands would be combined with existing 10 kHz splinters in adjacent bands to produce4 additional 20 kHz channels. Thiswould result in a total of 50 assignable frequencies in the largerbands 35.19-35.69 and 43.19-43.69MHz in place of the present 24.

Recognizing the needs of theSpecial Industrial Radio Service foradditional frequencies in the lowerUHF band, the Commission alsoproposed to allocate to that service, 14 of the newly assignablefrequencies to be derived throughthe channel splitting. These newchannels would be intended forregular two-way base and mobilecommunication ..

The Commission said furtherthat it would retain for commoncarrier one-way signaling servicethe presently assignable commoncarrier frequencies pl us 8 additionalone-way channels.

Four of the newly acquired channels would be allocated to theSpecial Emergency Radio Servicefor one-way signaling exclusivelyto meet the growing need for signaling service to doctors and othermedical personnel.

December, 1971

The cumbersomefour or more pieceFMmonitoringsystems are going.Belar Monitors do amore accurate job,as totally integratedone, two or threepiece systems.The FM Frequencyand ModulationMonitor measuresboth frequencydeviation andmodulation functions-the only unit to doboth. The StereoFrequency andModulation Monitorhas everythingbuilt in-phasediscriminator,exclusive 19 kHzfrequency meter,and test functions.The SCA Frequencyand ModulationMonitor is the onlyone that monitorsfour separatesubcarriers.All systems go!Buy Belar!

Write to:

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13



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Prime Time Rule ProposalIn response to a request by

Camellia City Telecasters, licenseeof KTXL-TV, Sacramento, Cal.,for a declaratory ruling concerningthe applicability of Section 74.1103(g)(2) of the rules (non-prime timeexception to the program exclusivity rule for network programs)the Commission has proposedamending the rule to make it applyalso to nationally syndicated programs released on a same-daybasis.

Section 74.1103(g)(2) now provides that the CATV system neednot delete a network programscheduled between 6 and 11 p.m.Eastern Time, but broadcast by thestation requesting deletion, outsideof the Prime Time period for network programming in the time zoneinvolved.

The Commission proposed toamend Section 74.1103 by inserting a Note I after 74.1103(g)(2) toread: The term "network program"

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includes programs nationally syndicated for release on a same-daybasis.

Camellia City said that viewersmay be deprived of the opportunityto watch many popular nationallysyndicated programs in prime timebecause a higher priority station onthe CATV system may schedulethe program later in the day, andunder the rules, may require theCATV system to delete any otherpresentations of the program, thesame day on another station onthe system.

The Commission said it foundCamellia City's argument "quitepersuasive", noting that in theSecond Report and Order in DocketNo. 14895, (2 FCC 2d 725, 749-750) it had stated that the reasonfor the non-prime time exceptionto the program exclusivity rule fornetwork programs was to " ... insure that such programs are available to the CATV subscribers inmaximum viewing hours."

Reid Joins CommissionUnited States Representative

Charlotte T. Reid, one of 12women in the House of Representatives, has been sworn in as aFederal Communications Commissioner in a ceremony at theWhite House.

Mrs. Reid was appointed on July2, 1971 to a full seven year termby President Nixon and confirmedby the Senate on July 29. Shesucceeds Commissioner Thomas J.Houser, who was appointed onJanuary 5, 1971 to finish the unexpired term of Commissioner RobertWells. Commissioner Wells wasnamed by the President to a fullterm as Commissioner on January5, 1971.

She studied music and voicewith Louise Gilbert in Chicago forseven years. During that periodshe sang on radio stations in theChicago area and from 1936through 1939 was a featured vocalist with the National BroadcastingCompany and on Don McNeill's"Breakfast Club," appearing underthe professional name of AnnetteKing.




The History Savers at work.~ ,.... _.,,,, -- '~""""""·_...._._,,...,.,,,,...,,..,,,,._,,"'""~·-·.-~- """*'""""'"""'"'·-·'-~

Deep inside a building at New York's LincolnCenter for the Performing Arts, recorded history iseing recorded again. At the Rodgers and

Hammerstein Archives of Recorded Sound,technician Sam Sanders is busy continuallytranscribing all sorts of old recordings, transcriptions and acetates. Not only will there then bea more permanent record of this valuable material,but access to it is made easy through a sophisticatedcatalogue system, by which interested persons canhear material that was otherwise unavailable.

The Rodgers and Hammerstein Archives ofRecorded Sound are part of the New York PublicLibrary, Research Library of the Performing Arts,and encompass virtually the entire history ofrecorded sound. But to get these early (and oftenirreplaceable) discs onto tape wasn't easy. Because

until the recording industry estab[ished its own standards, playingspeeds, groove widths anddepths were widely varied.

Stanton engineers workedclosely with Archive Head DavidHall and engineer Sam Sanders

'David Hall and Sam Sanders discuss a fine point.

when the Archive Preservation Laboratory was beingset up. Standard Stanton 681 cartridge bodies werechosen for their superior reproduction characteristics. However, some 30 different stylus types had tobe prepared to give the tape transfer operation thevariety needed to match the various old groovespecifications. Each was hand-made by Stantonengineers to fit a particular disc's requirements.So when Sam Sanders begins the careful disc-totape transfer, he must first match the stylus tothe record. Both microscope and trial-and-errortechniques must be often used together. But one ofthe special styli will enable every last bit ofmaterial to be extracted from these recorded rarities.

It goes without saying that a company willing totake such care in helping to preserve recordedhistory must also be interested in superior reproduction of today's high fidelity pressings. Which isone reason why Stanton cartridges remain the choiceof professionals the world over.

For an informative brochure aboutour professional-quality cartridges,write to Stanton Magnetics, Inc.,Terminal Drive, Plainview, N.Y.11803.

December, 1971


15



Understanding Zoom LensesPart 1 of 2 parts By Frank Bemish*

The advent of color and theplumbicon color camera has resulted in the television zoom lenscoming of age. One of the importantlinks in the video chain, it is probably the least understood. Whenproperly used, this lens can becomea valuable production tool.

A zoom, or variable focal lengthlens, consists of a marriage of fineoptics with good mechanical design. Each element is equally important to the correct operationof the lens.

Zoom Lens BasicsThe optics includes five basic

groupings of lenses. (Figure I)Starting from the front, the firstgroup of elements is used for objective focusing. These elementscompensate for the distance fromthe front of the lens to the subjectto be focused upon and performthe objective focusing. Generally,they are mounted so they move inor out with relationship to the restof the lens elements. The closer thesubject is to the lens, the furtherout the focusing elements will be·rele-Cine Corp.

16

from the rest of the lens.The focus elements are normally

controlled by the cameraman's focus control and represent the operational focus on a color camera.Directly behind the focusing elements are a set of condensing optics that essentially colluminate thelight, making the light rays perfectlyparallel. Thus, an image is presented to the moving zoom elements that is always in focus, nomatter what the position of thezooming elements.The third and fourth groupings of

elements are the main working partsof the lens. The third are the zooming elements and the fourth the

back focus compensation group.These two lens groups must movein definite relationship to eachother so that the lens will trackfocus throughout the zoom range.The zooming elements act, in essence, as a magnifying glass. As thelens is moved away from the objective focal point, this point is magnified. For example, the closer areading or magnifying glass is heldto the page of a book, the smallerthe print appears. Move the lensaway from the page and the printappears larger or closer to theviewer.You will note that as you move

the reading glass away from thepaper you must also change thedistance from your eye to the reading glass in order to maintain focus.1n the same way the fourth groupof lenses, the back focus compensation elements, work in relationship with the zooming elements.This relationship is controlled bya cam mechanism and it is thismechanical cam that is the heart ofthe successful lens operation. (SeeFigure 2.) This, more than anyother single element, determineshow well the total optical systemwill perform.The fifth and last general group

ing of optical elements is known asthe rear element and it determinesthe back focal length and imageformat size. This is an adjustmentfor the distance from the rear ofthe lens to the image plane of thetube or film.

Range ExtendersRange extenders, when used, act

ObjectiveFocusing

CondensingLenses


Optical Layout

zoomLenses

BackFocusLenses Figure 1

RearElement



as a magnifying glass increasingthe rear format size of the lens.Since the format size with a rangeextender becomes larger while theuseable format remains constant,the end result appears the same asincreasing the focal length, i.e.the picture appears to becomecloser to the viewer. The disadvantage of range extenders is thateach time the magnification is doubled. the light is halved. For example, 18 to 200mm f2. I lens witha 2.0x range extender becomes a36 to 400mm f4.2. In general, application light loss becomes sosevere in magnifications greaterthan 2.Sx that their practical usewith color TY cameras is limited.

Figure 2Zoom lens are designed to focus

track from minimum working distance (28". 4.0', 6.0', etc.) to infinity.This generally means that anythingfurther from the specified minimumworking distance of the lens willbe capable of being in focus throughthe zoom range.

Lenses with long minimum focallength will sometimes resort to aracking focusing movement or sliding the entire lens away from theimage plane in order to focus on anobject closer than the rated minimum working distance. This works;however, the lens will be in focusat only one point on the zoom rangeand cannot be zoomed. A zoomlens used in this way becomes afixed focal length lens.

Reducing Minimumfocusing Distance

One method of reducing the min-

December, 1971

Photos of Radio Comerciales S.A.. Guadalajara, Jal., Me>ico

How to get your shareof the Latin Americanbroadcast market.Right now, there are close to 6,000 radio and television stations in Spanishspeaking areas of the world. Competition among stations is keen. To remaincompetitive - and keep pace with Latin America's rapidly growing economytheir equipment must be kept in top condition. Clearly, a substantial marketexists for all kinds of broadcast equipment and components. New and used.

One publication - RADIO y TELEVISION- serves this vast purchasingpotential. It provides saturation coverage among buyers and those whoinfluence purchasing at broadcast facilities throughout Latin America andSpain. Owners, managers, engineers and technicians at commercial andeducational radio and TV stations, recording studios, electronic equipmentmanufacturers and related businesses.

As the Spanish-language counterpart of Broadcast Engineering, RADIO yTELEVISION delivers technically-oriented editorial aimed at helping readersto select, operate and maintain equipment and components for maximumsignal quality. This unique content provides the precise environment thatinduces buyer receptivity. It enables advertisers to "sell the broadcasterwhen his mind is on signal quality."

There's a lot more to the story. And we'd be happy to give you more information about this unique medium and the dynamic market it serves. Justcircle the Reader Service number or write directly to:

Radio y Televisión·The technical journal of the Latin Americanbroadcasting industry.

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17



He left the company. For good.Like 25,000 other valuable employeeswho lost their lives last year in autoaccidents.

Which has prompted a lot ofbusinesses to set up the NationalSafety Council's Defensive DrivingCourse. A course that utilizes testedconcepts and techniques of defensivedriving that can dramatically reducetraffic accidents among your employees.

Western Electric has already trainedhundreds of its employees how to driveand survive. So have other employeeconscious businesses Iike National CashRegister. Oklahoma Gas and Electric.And the Hartford Insurance Group.

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Figure 3

imum focusing distance is by theuse of a close up adaptor. (Figure3) This is an additional front lenselement that is attached to the frontof the zoom lens to reduce the minimum focusing distance. Threethings happen when a close upadaptor is used. The minimumfocusing distance is reduced bysome factor (0.5x). The zoom lensloses infinity focus, and you losesome light transmission. If a lenshas a normal minimum close focusing of 28" to infinity, when a0.5x close up adaptor is used, theworking distance now becomes 14"to 28" so you note that a close upadaptor is not used beyond its normal close working distance.

Manual ControlIt is normal practice to control

the lens from the operator position

•

at the rear of the color camera.This is accomplished by interconnecting the camera controls and thelens by means of a flexible shaftsimilar to a speedometer cable.Normally, manual control gives the

Figure 4

operator adequate flexibility with aminimum of effort. There are, however, limitations. Mechanical linkage, friction and operator physicallimitations show up when extremelyslow or fast zoom movements areattempted. The only practical wayof overcoming these problems is bymotorizing or servoing the lens.

Servo lenses have, in the past,been large and cumbersome andthe inability to have a manualbackup meant that servo down timeforced the loss of the camera. Whenthe plug-in servo module conceptapplied, a new era in servo lensuse appeared. Now lenses couldbe converted from manual to servoand back in the field. (See Figure4.) Newly designed DC servo systems give operational zoom speedsfrom one second to 12 minutes end

•

Figure 5Circle Number 19 on Reader Reply Card •




to end; and coupled with a shot boxwhich allows precise pre-setting ofshot framing and zoom speeds aswell as focus in some cases, anyoperator can easily perform movements that would be impossiblewith a manually controlled lens.

Business and Finance

In the next article, we will discuss technical setup procedures,maintenance and operating techniques that will give you the maximu111 performance from your lensand color camera.

Commission Adds CATV FormsFinal versions of two report

forms that must be filed by CATVoperators, FCC Form 325 (general information. CATV servicesand ownership information) andFCC For111 326 (financial information). have been adopted by theCommission (Docket 18397). Form325 will be due March I, 1972 andForm 326 will be due April I, 1972.The action amends Parts O and 74of the rules.

The Commission issued a rulemaking notice and a notice of inquiry on December 13, 1968 proposing that CATV operators fileannual reports providing currentinformation on such matters aslocation of the CATV systems:number of subscribers: channelcapacity: broadcast signals carried:extent and nature of program originations: any other operations conducted on the system: financialdata: ownership and interests inother CATV systems: broadcastmedia and other businesses.

The Commission said that it wasissuing its present order so theannual reporting requirement couldbe implemented as quickly as possible, even though the forms themselves will not be ready for severalweeks. Copies will be mailed to allknown CATV operators early inNovember. so they may study wellin advance of the filing deadlines,the Commission stated.

For both forms, the first reporting period will be calendar year1971. F or111 325 must be filed onor before March I of each year, forthe preceding calendar year, andForm 326 must be filed on or before April I of each year, for thepreceding calendar year. A CATVsystem that begins operation before December I, 1971 may reportfinancial information on a fiscalyear basis and must file annuallynot more than 90 days after the

December, 1971

close of the system's fiscal year.If a CATV operator is using afiscal year basis for Form 326,his first report should cover thefiscal year that began on or afterJanuary I, 1971.

Form 325

In the case of Form 325, onlynon-operating CATV systems willbe exempt from filing an annualreport. Program origination questions have been incorporated intothe CATV services section so thata separate program originationform is no longer necessary. Instead of requiring a separate Form325 for each CATV system. composite reports may be filed whenCATV systems are under commonownership and all the services andownership information requestedby the form is identical.

The CATV services section ofForm 325 asks about programsources (local, automated or videotape), types of programming andnumber of hours of each duringthe "specified week" for reporting. The specified week is definedas the seven-day period beginningat 12:01 a.m. on December I, 1971and ending at midnight on December 7, 1971.

If it is impossible for CATVsystems to use the specified week,they may use any seven consecutive days of the 60-day period immediately before the date of filingof Form 325, as long as they explain the reasons for not using thespecified week and indicate thedates that are 'being used instead.A proposed rule requiring CATVsystems to maintain program logswill permit future reporting to bebased on a composite week, theCommission stated.

Adoption of Forms 325 and 326became effective November 22,1971.

Number 86 in a series of discussionsby Electro-Voice engineers

A major problem of microphone design in thisera of the hand-held directional microphone isthe reduction of noise transmitted to the diaphrag m through the microphone case. The difficulty is most acute with the so-called"Sing]c-D" cardioid models.

While the conventional approach is to isolatethe entire microphone element from the case,difficulties arise in choosing suspension parameters and materials that will be equally effective at all frequencies. Thus, coupling of theelement to the case may vary with frequency.And because the mass of the entire elementdiffers from the mass of the diaphragm assembly alone, any axial motion of the elementwill cause the diaphragm to move relative tothe element (and voice coil gap) thus converting the motion into electrical energy and audible noise.

A novel suspension system has been developedby Electro-Voice that uses the noise energyitself to reduce shock noise. Using an extremely compliant ring suspension, the elementis isolated from the case, but relatively free tomove axially. Behind the element, an air volume is connected by an inductive passage tothe air space behind the diaphragm. This airvolume is contained in a compliant "píston"that attaches element to case to act as a formof shock absorber controlling axial elementmotion.

As the element moves with respect to the case(inward, for example) the trapped air is compressed by the piston, exerting pressure on theback of the diaphragm. This forces the diaphragm to move with the rest of the element.In this manner, element motion and diaphragmmotion are kept in step, and there is vastlyreduced electr-ical output from shock noise.

Testing indicates a reduction of shock noise byan order of 20 dB compared to conventionalshock mounting. And the concept seems especially effective at frequencies around 130 Hzwhere shock noise energies are high. Becausethe system need not affect response or directional characteristics, greater design freedom isassured for optimum performance. The systemis now in use in the Model 670 Sinale-D Cardioid microphone and will be included in 2new microphone designs, the DS30 and DS3fisoon to reach the professional microphonemarket.For reprints of other discussions in this series,or technicaldala on any E·Vproduct, write:

ELECTRO-VOICE,INC., Dept. 1213V638 Cecil St., Buchanan,Michigan 49107

19



The New Remote Control VIT Signal

This new ruling will still require a First Class Operatorfor the remote monitor. If properly used,this method could improve the TV signal quality.By Bruce Longfellow I Rules and Standards Div., FCC.

Commission experience in authorizing the remote control of television transmitters-extending fromthe first actual UHF remote control operation in 1963 through extensive VHF testing by NAB andothers-has emphasized the pressing need for improved control overthe quality of the transmitted picture.

The almost complete conversionto color since remote control wasfirst authorized has added an entirely new dimension to the problems of transmitter operation andmaintenance, while the separationof the operator on duty from histransmitter and control console hasmade it plain that more, not less,attention to the quality of thetransmitted picture is needed.

The Commission has concludedthat, in order to best achieve thisrededication to highest possibletechnical quality, appropriatemeans must be provided for thestation's engineering staff to be keptfully aware of transmitted signalcharacteristics at all times. Consequently, in authorizing VHF transmitter remote control operation, theCommission determined that suitable locally-generated test signals inthe vertical blanking interval wouldbe required for all transmittersUHF as well as VHF-when operated by remote control. After receiving comments from all segmentsof the industry as to the nature ofthe test signals, the Commission inits Second Report and Order inDocket # 18425 adopted the newtest signal requirements. This

20

article will describe the new testsignal, discuss the basis for itschoice and explain what the Commission does and does not expectof television licensees who employit.

The adjustment of a televisiontransmitter for proper operation requires the employment of test signals of controlled characteristics.These signals normally are utilizedonly during maintenance periods,and are transmitted over the fullpicture raster. However, the abilityto transmit test signals along withpicture information has a recognized value for detecting and identifying performance deficiencies occurring during regular operation.

Such signals may be generatedlocally and transmitted in the vertical blanking interval during regular programs under an FCC rule onits books for a number of years.'Generally, however, the only testsignals radiated in the vertical interval have been those generated bythe networks, used in the maintenance of long network lines, andintended for observation at the lineterminals. Under the rule, these signals need not be erased beforetransmission, and in the usual case,the television station radiates thenetwork test signals along with thepicture. Although these test signalsmay be observed at the transmitteroutput to assess transmitter performance, the degradation they sufferin traversing the network linesmakes them of limited value intransmitter testing. Moreover, therelative and absolute levels of the

signals are not in all cases the bestchoices for transmitter surveillance.

New RequirementsThe new remote control rules re

quire the transmission of test signals of specified characteristics inthe vertical interval during all periods of regular programming. Withone exception discussed below,these test signals are to be insertedin the vertical interval at the remote control point, and, after radiation, to be received and observedthere, with the results of observations logged at half-hour intervals.At the remote control point, thetransmitter operator has controlover these signals, and may whenever desired compare the input testsignal with the output signal as received over the air.

If the remote control point is notat the studio, this requirementposes obvious problems, since theSTL input ordinarily would not beaccessible at the remote controlpoint. Since a single location forperforming all of these functions isdesirable, the remote control location should be chosen with due regard for this problem. Remote control applications specifying a remote control location other than themain studio (Question 5(c) of FCCForm 301-A) require an explanation of the choice of location. Ifthe test signal is inserted at such alocation, a waiver of the Commission's rules is required. Any suchproposals should include full justification, including the provision of




NOTES:1. A breezeway, as shown between

bursts, is recommended. Eachburst= 60 IRE units peak to peak.

2. To·= Nominal start of active portion of line 18, field l.

3. Rise and fall of white bar shallhave risetime of not less than0.2 (JS.

~irr i. '~·:ii

'>r

,._.o. ll·.

NOTES:1. Phases and amplitudes of the

colored bars are in accordancewith the FCC Rules and Regulations for 100% saturated colorsof 75% amplitude.

2. White flag (bar) at referencewhite precedes the colored bars.

3. A black bar at setup level followsthe colored bars.

4. Each bar6µsminimum duration.5. To= Nominal start of active portion of line 18, field II.

NOTES:1. Sub-carrier of staircase in phase

with burst.2. Rise and decay of all luminance

signals not less than 0.2 usec.Rise and decay of envelope ofsub-carrier component of stairstep signal shall be approx. sin2

shaped and risetime .375 J.ISec.3. To= Nominal start of active por

tion of line 19.

"half amplitude duration

December, 1971

..~100

70

rf {'• I

40

10

o

-40

MUL TIBURST TEST SIGNAL1FIELD 1. LINE !81

-,

S "'VWI•

...I'¡1~

To

100%

I5!

Fig. 1 VIT waveform required for field 1, line 18.

7.5

o

-40

100

COLOR BAR TEST SIGNAL(Fl ELD 2, LINE 18)

12.5 %

~>w...•"'wii"'«.. u

"~..~owo~;;¡

75% ~w..

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WHITE YELLOW CYAN GREEN MAGENTA RED BLUE BLACK

To Microsecond, (J.,,J, To -,.Q 52

Fig. 2 VIT waveform required for field 2, line 18.

100

o

COMPOSITE Slet-IAL(FIELD 1, LIME19)

-40

0.25 usec " 1.571 µsec*2T sin2pulse 12. ST modulated sin2pulse

~I n/1100 12.5"1,

...•>w...•"'ws..u

"~~owo..•...;;¡u

75"" ~..

14reo~

04

w ••km~ ' 44

32

201 u:16 I

12 II-o-l_J II I I I I I I

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II I

I I I I I I I IIO 13 16 19 22 26 28 34

To Micro~~condl (.ui), To~ O

I52

18USEC•

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.. ,.Fig. 3 VIT waveform required for field 1, line 19.

21



~

VITS fLJLL vrrs E118 fl£l0 1!J

A<b ':,~"' B<P l

,,,...,~HANNELA~H1~' GAIN

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INTENSITYLUMINAll;Cf.

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I IFig. 4 Vectorscope display of color bar test signal on line 18,field No. 2, showing color bars inproper amplitude and phase.

complete system surveillance fromthe remote control point.

Signal InsertionThe test signals are to be inserted

on lines 18 and 19 in the verticalinterval and will occupy line 18 inboth fields and line 19 in field No.1. The signals to be employed andtheir characteristics are those proposed by EIA in the rule-makingproceeding.

In summary, these signals are:Field No. 1, line 18. Multiburst,preceded by white flag (See Figure 1).Field No. 2, line 18. Color bars,preceded by white flag (See Figure 2).Field No. 1, line 19. A composite signal, consisting of thesequential transmission of a fiveriser staircase, each tread addedto color subcarrier phased lockedto the color burst, with a peakto-peak amplitude of 40 IREunits, a 2T sine-squared pulse, a12.ST pulse modulating colorsubcarrier, and a white flag of100 IRE units in amplitude and18 µ.S in duration. (See Figure3).Normally, the line 19 composite

test signal would also be insertedon field No. 2 at the remote control point, but it may be inserted atthe transmitter input if a stationlicensee desires to make a separatedetermination of the effect of histransmitter and studio-transmitterlink on system performance. Alternatively, the licensee is permitted

22

to insert test signals of hisown choosing on line 19 of fieldNo. 2 either at the remote-controlpoint or at the transmitter, provided that the insertion levels andother characteristics of the signalsresult in no interference with theobservation of the required signalsor with the transmitted picture.

The levels are standardized asshown in Figures 1, 2, and 3. Theaverage picture levels (APL) of thesignals have been balanced for eachfield, and the components are soarranged as to reduce the possibility of interference between test signals. For monochrome transmission, the chrominance componentof the color bars is removed.

Lines 18 and 19 were selectedfor the locally-generated test signal transmissions to protect tentative commitments for the use ofother lines which are available under existing rules. Line 17 is beingconsidered for the transmission oftest signals accompanying programsintended for international distribution, and line 20 may be occupiedin the future by a vertical intervalreference (VIR) signal which isbeing developed by an industrycommittee (See January, 1971BROADCAST ENGINEERING).The VIR signal would accompanya color program from its source,and would be used to detect distortion introduced at any point in thetransmission path which might adversely affect color quality.

Television engineers are generallyfamiliar with all of the test signalsdescribed, and employ some or all

in the testing and adjustment oftransmitter during maintenance periods. The primary uses of thesesignals are well-known: the multiburs t for transmitted videoamplitude vs. frequency responsemeasurements, color bars for ascertaining the ability of the system totransmit color components in thecorrect relative amplitudes andphases, the staircase for the measurement of dynamic gain, and differential gain and phase, the 2Tpulse for the observation of transient response, and the white bar forlow frequency phase characteristics.

The 12.5T pulse is used forchrominance/luminance delay measurements in lieu of the more familiar 20T signal, since the frequency spectrum of the 12.5T pulsemore closely approaches that of theNTSC 525-line color signal thandoes the 20T pulse. The signal foreach field includes a white bar at100 IRE units, which may be usedas a reference level.

Employing Test SignalsThe rules do not specify the way

in which particular test signals areto be employed, and each licenseeis expected to develop his own procedures. For example, the multiburst signal may be employed toobserve the video amplitude vs.frequency response while for colortransmission the color bar test signal may be displayed on the vectorscope (Figure 4).

Likewise, appropriate use may




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be made of the other elements ofthe test signals to determine a widevariety of transmitting system parameters. Examples of typical insertion and test equipment, togetherwith oscilloscope displays areshown in Figures 4 through 6.

Test signal observations are required to be made immediately aftercommencement of operation, andduring operation at intervals notexceeding one-half hour. More frequent observations are to be madeif necessary to insure proper performance of the transmitter and associated equipment. The date andtime of each observation of the testsignals must be entered in the operating log, together with notationsas to the results of these observations.

Test Signal DistortionThe received test signals may be

distorted to some extent because oflimitations in the monitoring system itself, and not necessarily as aresult of transmitting system deficiencies. Concern was expressed bysome persons commenting in therule-making proceeding that theFCC might use test signal observations as a basis for issuing noticesof violation although observationsbased on the test signals might notnecessarily accurately reflect theperformance of the transmittingsystem. This was cited by some ofthe parties as a reason that specifictest signal requirements should notbe set by rule prior to extensivetesting.

The FCC recognizes that suchdistortions may occur, but does not

24

Fig. 5 Waveformdisplay of composite signal on line 19.The 12.ST pulseshows correct amplitude response at3.58MHz,with neg-1 ig ible envelopedelay.

believe that this substantially lessens the utility of the test signalsfor surveillance of the transmissionsystem. This does require, however,that the monitoring system be carefully designed and installed, andthe rules require that the waveformmonitor at the remote control pointbe periodically calibrated against amonitor maintained at the transmitter.

Multipath propagation of the signal between the transmitter and theremote control point is an obvioussource of distortion. At the remotecontrol point, its effects may beminimized by the proper selection,sitting, and orientation of the receiving antenna. On the other hand,this would not always be possiblewhen the monitoring of test signalsis undertaken with a mobile unit.Thus the FCC would not rely solelyon off-the-air observations of testsignals in detecting deficiencies intelevision station operation, butwould follow up apparent deviations with observations at the transmitter.

In any event, the test signal requirement is not being adopted asan enforcement tool, but to give thetelevision station licensee a moreeffective and meaningful methodfor monitoring the daily operationof his transmission facilities.The other major source of dis

tortion may be in the demodulatorwhich feeds the waveform monitoror vectorscope for test signal observations. Quadrature distortion isproduced in an envelope detectorwhen the portion of the televisionsignal which is transmitted in the

single sideband region (this includesthe color subcarrier) is demodulated to baseband, and is moresevere the higher the level of thesignal component relative to thecarrier at the demodulator input.It is manifested, among other things,in inaccurate indications of differential gain and phase at the colorsubcarrier and distortion of thechrominance/luminance relationship.

The effects of quadrature distortion on a test signal may be minimized by reduction of the amplitude at which the test signal istransmitted. The specified multiburst signal is limited to a peaklevel of 70 IRE units primarily forthis reason. The reduced amplitudeof this signal also lessens the possibility that intercarrier buzz may result from its transmission.

How serious a problem this kindof distortion will present dependslargely on the demodulator characteristics. A number of demodulators of recent design incorporatefeatures intended to limit quadrature distortion. A "state of the art"demodulator, which the FCC rulesrequire be installed at the remotecontrol point, should include suchfeatures as a minimum. Likewise,where a signal frequency amplifiermust be used to raise the level ofthe off-the-air signal delivered tothe demodulator, it must be of suchquality as not to limit monitoringsystem performance.

Residual distortions normallywould be identified and accountedfor by appropriate calibration procedures. While the rules do not require it, this procedure may be simplified if the waveform monitor atthe transmitter output against whichthe remote monitor is calibrated isfed by a demodulator of characteristics identical to those of the demodulator at the remote controlpoint. This is particularly true,since both demodulators shouldhave the same degree of quadraturedistortion, and for regular operation must be operated with thesound notch in, which will modifythe indicated response from that ofthe visual transmitter itself.

In some cases there may besignificant differences in the per-




formance of a transmitter whenhandling vertical interval information as compared to program material. These differences should beidentified by full field/vertical interval test signal comparisons in thecalibration procedure.

Since lines 18 and 19 may beoccupied by network signals, andexcess noise may be present, erasing facilities must be employed before the locally-generated test signals are inserted at the input to thestudio-transmitter link.

New Equipment ComingTo permit station licensees to ob

tain the necessary signal generatingequipment, the FCC has postponedthe implementation of the test signal requirement until April I,1972.The FCC expects that well be

fore the effective date of the testsignal rules, signal generators capable of providing all of the requiredtest signals will be available. Suchgenerators will incorporate facilitiesfor erasing incoming signals andnoise from lines 18 and 19, and forinserting the test signals directly onthese lines. While these generatorswould seem to offer the simplestand perhaps most economicalmethod for providing the requiredtest signal input, the television licensee is not precluded by the rulesfrom employing any combination ofseparate signal generators and aux-

iliary equipment which will producetest signals of the specified characteristics.

Off-the-air test signal observations are not expected to providean absolute measure of transmitterperformance, but rather are reliedon to indicate departures from normal transmitter performance determined at the time the off-the-airmonitor is calibrated. Thus, thebroadcaster is not expected to makea detailed evaluation of the characteristics of the test signals whenthey are observed and logged eachhalf hour-only significant deviations from normal transmissionneed be specifically noted and analyzed.

The FCC has no immediate intention of establishing standards fortype approval of vertical intervaltest signal generators, or for otheritems of equipment, such as demodulators, whose performancecharacteristics may affect test signaltransmission and observation. Thedevelopment of standards, and particularly the subsequent testing ofvarious manufactured units forcompliance with these standards,can be extremely time-consumingand would unduly delay the implementation of the test signal rules.

The broadcaster can best assurethat the apparatus he acquires is ofsatisfactory quality by a carefulstudy of detailed specifications,which any reputable manufacturerwill supply, of any piece of equip-

( ) PROGRAM CONTROL

Fig. 6 Typical instruments for generating and inserting the vertical interval test signals.

ment he has under consideration,with due regard to the requirements of the rules.

In adopting rules requiring theregular transmission and observation of vertical interval test signalsby television stations operating byremote control, the FCC is providing a new, and it believes, moreeffective means for the continuingsupervision of television transmission systems. As the broadcastergains operating experience underthese rules, the need or desirabilityfor their modification may becomeapparent. The FCC would appreciate suggestions from the broadcaster, or reports in problems encountered.

If, as is hoped, this method oftransmitter supervision becomesfirmly established and accepted foruse by television broadcast stationsoperating by remote control, consideration may be given to the extension of the requirement to alltelevision broadcast stations. Atthat time, it may be appropriate toconsider the relaxation of ruleswhich require the half-hourly logging of the traditional operatingparameters. A

Footnotes173.682(a) (21): "The interval beginning with the last 12 microseconds of line 17 and continuingthrough line 20 of the verticalblanking interval may be used forthe transmission of test signals ... "

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December, 1971 25



Multiplying, mixingand modulating with /C'sPart 2 of a two-part series ay wait Jung

Last month we talked of the balanced modulator in IC form asexemplified by Motorola's MC-1596/1496 chips. The balancedmodulator by itself is certainly animportant enough IC development,but it is more than that. It alsoforms the basis for a completelylinear four quadrant multiplier, acircuit which performs circuit functions previously impossible or economically unfeasible.

The four quadrant multiplier operates with two linear voltage inputs (X and Y) in the range of-+-10 Volts and generates an outputsignal which is the product of thesetwo inputs times a scale factor, "K".Therefore the output is of the formEo=K Ex Ey where K is the scalefactor and Ex and Ey are the X andY inputs. As in the balanced modulator, the device is termed four

OUTPUTKXY

21 14

Ii ••

quadrant, because the output willalways possess the correct algebraicsign with any combination of Exand Ey polarities.

This month we'll look inside thistype of IC to see how it works andalso explore a few applications useful to the broadcast engineer.Among the applications of the fourquadrant multiplier are: modulation and demodulation, phase detection, frequency multiplication, electronic gain control, audio or videoswitching, voltage tunable filters,and power computation.

Heart of the FourQuadrant Multiplier

Last month we described how amonolithic balanced modulator performs the process of multiplyingtwo inputs. This is accomplished bythe two inputs to the device, termed

DI

-V

26

Fig. 1The MC1595/1495,a linear four quadrant rnultiplier ,

the "signal port" and the "carrierport" on the MC1596/1496. InFigure 1 you will note a very closesimilarity to the MC1596/1496contained in the left hand portionof the circuit. This circuit is ofcourse a balanced modulator also,the only difference being the addition of Darlington connected drivers to Q5 and Q6. The biasing network of Q7-Q9 is identical to theMC1596/1496, and the collectorcurrents of Q5 and Q6 feed a quadset of current mode switches, OIQ4, just as in the MC1596/1496.But note the base drive for Q 1-Q4-not from the external world, butfrom another circuit (the right handportion).

The reason for this additional circuit is the difference in concept between the basic balanced modulator(as typified by the MC1596/1496)and a fully linear four quadrantmultiplier such as the MC1595/1495 (which is what the schematicof Figure 1 shows).

Last month we discussed the signal handling capability of the MC-1596/ 1496 carrier input or thequad transistor set of Ql-Q4. Thesetransistors only exhibit a linearvoltage input/current output transfer for small signal levels; 50mv orless. For signals much beyond, linearity suffers, and compression ofthe transfer characteristic begins tooccur. Further increases cause moresignal compression, until beyond acertain input signal level, full limiting occurs.

The distinction we are makinghere is that the basic balancedmodulator (MC1596/1496) is bestsuited as a switching mode type ofmultiplier because of this naturallimiting characteristic of the carrierinput transistors Ql-Q4. To realize




I¡i

02

DI

Fig. 2 Illustration of linear current control through non-linear processing.

a completely linear transfer characteristic through this port, someadditional monolithic matchingtricks are brought into play.

Linear CurrentTransfer Through

Non-Linear ProcessingIf we consider a pair of identical

transistors (such as those readilyavailable through monolithic matching) we will note some very basicproperties which can be broughtinto play in a highly useful manner.In Figure 2, Dl and Q2 are amatched pair of transistors with Dldiode connected and in shunt withthe base of Q2. It is a well knownproperty of a semiconductor diodethat its forward voltage drop islogarithmically related to the current flowing through the junction.In Figure 2, Dl is such a diodeand will exhibit a drop (which isalso its Vbc) which is logarithmically related to Il. Note that forlinear current changes in Tl, theVbc of Dl will vary in quite a nonlinear fashion, since it is logarithmically related.

But now consider the effect ofQ2. The collector current of a transistor is exponentially related to itsbase voltage. This also is non-linear;the voltage changes required in Q2'sVbe for linear collector currentchanges are very small and not related in a linear fashion.

Now relate these two phenomenato the original assumption of identical transistors for D 1 and Q2. Fora given le the Vbe's of the twotransistors will be identical. Statedanother way, if a current 11 is fedinto Dl it will naturally develop aVbc across Dl which is logarithmically related to this current. Butsince Q2 receives this same basevoltage, its collector current will be

December, 1971

an exponential function of it. Sincethe two are ideally matched, I2 willbe equal to 11!

It also follows that equal changesin Tl, will result in correspondingequal changes in I2. So we can seehow two non-linear transistor properties can be utilized to realizelinear current transfer through theuse of matched transistor propertieswhich cancel the non-linearieties incomplementary fashion.

Now we can relate this propertyto Figure 1 in a couple of stepsand see how a complete linearization of the Y channel signal inputtakes place. First, refer to Figure3, which is a simplified model ofthe multiplier with the non-linearprocessing. Diodes Dl and D2 represent the logarithmic elements similar to Dl to Figure 2. These twodiodes receive the equal and out ofphase currents from the Y channelinput differential pair. These twosignals are shown as -j-Ly and -Iy.So far this stage operates just as thesignal port we discussed last monthfor the MCl 596/ 1496, with the exception that loads for this stageare the diodes Dl and D2.

+V

RL~ RL+K Ex Ey l I -K Ex Ey

Now you will also note that Dland D2 are in parallel with theupper port quad transistors (QlQ4) of the balanced modulator.And just as we talked of matchedtransistors for the development ofFigure 2, here we will consider allof the Ql-Q4 set and Dl-D2 identical. It is quickly apparent whathappens now. The differential logarithmic voltages across Dl and D2exactly complement the drive requirements for non-linear voltagecontrol of Ql-Q4. As a result thecurrents -l-Iy and -Iy control therelative conduction of the Ql-Q4set in a linear manner, although themeans of control is decidely nonlinear.

Let's review what has been accomplished in this process. We havetwo linear input signals, Ex andEy which are converted into corresponding currents proportional toRx and Ry. These currents appeardifferentially as -+-Ix and ±Iy.±Iy is processed logarithmicallyand used to control one input of abalanced modulator (Ql-Q4). Theother input to the modulator is±Ix. These two inputs are multi-

DI Y 02

+ ...•~~~--#--~~~~~~~ .......•~ Ey

-V

I ,. +

-V

Fig. 3 Basic model of a four quadrant multiplier.Circle Number 22 on Reader Reply Cord -II

27



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plied within the modulator and appear at the output resistors as+KExEy. Just as in the basic balanced modulator, these output signals are four quadrant, always possessing the correct sign for all input polarities. The scale factor "K"is set by the resistances Rx andRy in relation to RL and the ratioof Y channel current to X channelcurrent. Both signal inputs are differential and can handle DC as well

l OUH'UT·JN I I I " OHSCT

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Fig. 4 Test circuit for the MC1595/1495.

Fig. 4a Scope pattern for the MC1595balanced modulator.

Fig. 4b Scope pattern for the MC1595as a modulator.

38

as AC signals.If we tum back to Figure 1 we

see how this all goes together in asingle chip as Motorola's MC1595/1495. This chip is in a 14 pin dualinline package and contains all thecircuitry shown in Figure 1 (withthe exception of the Rx and Ryscaling resistors). As was true forthe MC1596/1496, you will notethere is little internal commitmentof signal leads; rather, all pertinentpoints are brought out to the userfor flexibility.

Biasing of the X and Y differential input channels is identical tothat of the MC 1596/ 1496: selection of a single external resistorsets the current in the differenitalamp. The X and Y biasing taps areseparate, however. This facilitatesscaling of the relative bias ratiosbetween the two channels. The biasconnection for Dl and D2 (Vern)is brought out for external connection.

Setting up theMC1595/1495for Operation

Now that we have dissected thegadget and exposed its inner workings we'll want to put it to workin a few applications. We'll begin bytalking of a few parameters important in applying the device and thenprogress into some useful circuits.

The first step in setting up anMC1595/1495 is the DC biasingrequired to properly operate the device within its linear range. Let'slook at a typical operating condition and see what this means circuitwise. Figure 4 illustrates a typicalmultiplier circuit set up for an Xand Y input range of ±10 Voltsand an output swing of +10 Volts.Under these conditions K is equalto 1/10. X and Y channel bias currents are set to 1 ma by R3 andR13, with R3 made variable (moreon this in moment).

For good linearity, the dynamiccurrent in Rx and Ry is not recommended to be more than 213 thebias current at pin 3 and 13. Thismakes Ix and Iy .67 ma max, andwith Ex and Ey 10 Volts max, Rxand Ry then become 15 K.

The value of the load resistorRL is determined by the scale factor K, Rx, Ry, and I3 according to

the relation K=2RL13Rx Ry.

Since all of these factors areknown, we can easily solve for RLand it is found to be l l .25K. Andsince the scale factor is also dependent upon I3, trimming this currentallows a precise value of K to beset. So we can use an 1lK resistorfor Rl and set K to exactly 1/10by trimming R3 with the SK pot.

The remaining resistor, Rem, isselected to drop the difference between the supply voltage (here 32Volts to allow a 10 Volt swing ateach RL) and a voltage high enoughto insure non-saturated operation ofthe Y channel input transistors.Since these transistors must swing+ lOV max, 3 Volts is added forsafety. Then this plus the .7 Voltsof Dl-D2 places pin 1 at i3.7Volts. Then Rem= 32-13.7 =

2 ma9.15K or, since this voltage is notcritical, the nearest standard valueof 9.lK is used.

These conditions set up the basicoperational conditions of the circuit"ball park" so to speak. But forprecise operation, the conditionswill need to be trimmed more closelyto optimize things. This is similarto the carrier balance technique usedwith the MC1596/1496, but in thiscase there are more adjustments.There is a definite procedure recommended, which goes as follows:(l)With Ex and Ey=O, adjust outputoffset (Pl) to zero. (2) With Ex=5v, Ey=O adjust Ey offset (P3)until output is zero. (3) With Ey=5v, Ex=O, adjust Ex offset (P2)until output is zero. (4) With Exand Ey=O, adjust offset (Pl) tozero. (5) With Ex=Ey=5v, adjustscale factor (P4) until output is 2.5v.(6) With Ex=Ey=-5v, insure thatoutput is correct at 2.5v. If out oftolerance, repeat steps 1-5.

Having properly set the multiplier up for correct operation, itwill now operate according to specification. The MC1595 has 'a maximum output linearity error (in percent of full scale) of 1 percent forthe X input, a 2 percent for theY input. The MC1495 has maximum allowable errors of twice thesefigures for the same conditions.These tests are at 25ºC and usingthe circuit of Figure 4, which is in




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December, 1971 39



+15v..,.~....-----.....--..--- ....•.--~

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I :2 14 o911

Rx~ B. 2K12 MQl595

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IKIOK

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Fig. 5. Squaring circuit or frequency doubler.

Fig. 6. MC1595 frequency doubler waveforms indicating less than 1% distortionwith no filtering.

fact Motorola's test circuit for thedevice.

The circuit of Figure 4, althoughit is a test circuit, can be useful alsoas a working circuit. For use withAC signals, the output can betaken from pin 2 or 14 through aDC blocking capacitor (or capacitors). This circuit can be usefuljust as is for a linear balanced modulator (Figure 4A) or AM modulator (Figure 48) (with appropriatecarrier insertion offsetting the carrier balance). Frequency response is3 dB down at 3 MHz typically withthis circuit, making it useful wellinto the lower video region as wellas at audio frequencies.

40

.16.BK

TANTALUM

hlµF ~

-15V

As in the MC1596/1496, thisone also can be used for demodulation by multiplying a modulatedcarrier times a local synchronouscarrier and low pass filtering theoutput to recover the modulationproducts. Hence the name "productdetector".

Again, as was true with the MC-1596/1496, the MC1595/1495will double an input frequencywithout tuned circuits and withminimum distortion. The MC1595/1495 also has the big advantage ofa much wider dynamic range. Figure 5 is a squaring circuit (whichdoubles a single input frequency orsquares a spectrum) optimized forthis particular use. Note that offset adjustments are still used to insure accuracy. In this circuit the Xand Y offset adjustments are madeinitially with the X and Y inputsseparated (steps 2 and 3). There isno output offset adjustment forthis circuit. Then connect X andY and apply an AC input and youwill get a waveform like Figure 6.

DC ApplicationsFor DC applications the output

of the multiplier must be directlycoupled. A differential DC signal is

available between pins 2 and 14 ofFigure 4. However this signal rideson a 21 Volt DC quiescent level,and in many applications it may bedesired that a DC output be centered around ground. Figure 7 isanother general purpose multiplier,but in this case it can be completely DC coupled with an outputwhich rides around ground quiescently. Note also that it operatesfrom + 15 Volt supplies.

This circuit uses a multiplierblock with a scale factor of 1/75and an op-amp level converter witha gain of 7.5 to give a net scalefactor of 1/10. The op-amp amplifies the differential signal from themultiplier and shifts the DC leveldown to zero at its output. The output offset control allows adjustmentof the output DC level to null boththe offset of the multiplier and theop-amp. Setup procedure for thiscircuit is the same as that describedfor Figure 4.

Viewed As A SystemSo far we've discussed a few cir

cuits and how they work on twovoltages. But a better appreciationof the device can be had if it isviewed on a system basis. To dothis let's now visualize applying thecircuit blocks we've discussed insome systems.

Figure 8 is a good example ofwhat can be accomplished with theversatility of the MC1595/1495multipliers. Here a pair of multipliers are connected as complementary gain controlled stages with again control voltage applied to theY channels. The X channels are fedtwo signals which are to be controlled, A and B. The control voltage is a O to + 10 DC signal. Operation is as follows.

The A channel multiplier operates as a voltage controlled amplifier. Its range of gain extends fromzero with Vc=OVDC to maximumwith Ve=+ lOVDC. The B channel multiplier operates as the exactcomplement of this; its range of gainextends from maximum with Ve=OVDC to minimum with Ve=+IOVDC. With this arrangement thesingle control voltage controls thedegree of gain of both channelsfrom minimum to maximum oranything in between. The outputsof the two multipliers arc combined




in an op-amp summing circuitwhich also buffers it to a lowsource impedance.

Versatility Of AVoltage Controlled Stage

There are many things you cando with a voltage controlled stagesuch as this. If signals A and Bare two audio inputs, a pot supplying the O to 10 Volts DC controlwill serve as a remote fader control.In fact if suitable attention is paidto optimizing the bandwidth of themultiplier circuit and the summingamplifier, this circuit can be usefulat video frequencies as well asaudio.

This provides a tremendous advantage to switcher/fader design asa single control voltage providescomplementary control of two videochannels, allowing smooth transitions from one to the other withoutclumsy attempts to make two different ganged fader pots track, asituation which although theoretically realizable is a near impossibility in practice.

By going a step further you canautomate the control by using aramp generator as shown. With individual control of ramp times youcan make programmed fades fromone channel to the other. Althoughthe schematic shows push-buttonswitches to initiate the fades, thiscould also be done by control logicand thus be completely automated.The fades you will get with a circuit like this will always be smooth,linear and perfect, and with the selection of ramp times, easily adjustable to create the desired effect.

You can carry the idea of theramp control a step further andapply it to special effects videoprocessing and come up with somevery unique results. This is illustrated in Figure 9, which showswaveforms corresponding to thecircuit of Figure 8. Here two videoinputs A and B are switched by atrapezoidal control signal, shownhere in approximately the middlethird of a single TV line.

Note that as A is fading to zero,B is rising to maximum. On thetrailing edge of the switching waveform the reverse is true. During theperiod or the switching transistionportions or hoth video waveforms

December, 1971

will appear on the screen, giving a"soft" transistion between the two,a "movie-like" effect not hertoforepossible with TV techniques. Control of the switch transistion timesand the shape of its slope (linear,"S-shaped") will give creative control over the resultant image.

Another version of a voltage controlled attenuator with wide usefulness is an AGC system. By rectifying a portion of the AC output signal from a multiplier and applyingit back as a voltage control, auto-

matic level control can be implemented.

Summing UpThe listing of linear multiplier

applications could go on and onindefinitely, for the potential applications of a device such as this goas far as there are requirements forsolving for the product of two variables. Just as is true with the operational amplifier, imagination isthe only real limitation to the useof the 4 quadrant multiplier.

•l5VI I

RL!UK TANTALUM!l¡Jf

RL UK

l.21\ l21K

!OK • 34lOOK

Ex l 1 14~IOV ' 10 ~llK

11(y MC1595

OR:1ov 4 MC1495

8

J lllK Pz !OK

-lOK

lK tlOK dlKfl~

"ANTA LU-;j}=-

l¡i't

-15V

P1 OUTPUT OFFSET

~tmeq

13.7K

~HOKEdy

ro·w-

NOTES: ·OP AMP IS 741 TYPEOR OTHERINTERNALLY COMPENSATED UNIT.

Fig. 7. Direct coupled general purpose multiplier with buffered output.

veCOllTROLSIGNAL

FADE RATE

I i "i~ t...l..Sl fAOf UPUPIO OWN

A CHANNEL ON _ _ RAMP- - - - - GENERATOR·~••oon-T~.,. - ~ -'-~''"'"-º

•.¡av

Fig. 8. Voltage controlled mixer.

41



In these two articles we've triedto lay down the groundwork of thecircuit concepts behind the monolithic balanced modulator and thefour quadrant multiplier. You maywant to learn more of this fascinating class of devices, so we are including a list of application notesand data sheets which are concerned with the multiplier concept.You may write to Motorola on yourcompany letterhead at the addresslisted to obtain further information .

•••Application Notes-AN 531: MCl 596 Balanced

Modulator.AN489: Analysis & Basic Opera

tion of the MC1595.AN490: Using the MC1595

Multiplier in Arithmetic Operations.

AN491: Gated Video AmplifierApplications The MC1545.

AN475: Using th e MC1545-A Monolithic Gated Video Amplifier.

AN432B: A Monolithic Integrated FM Stereo Decoder System.

SWITCHTRANSITION---i f4-

SWITCH¡TRANSITION

SPECIAL EFFECTS - _, r-CONTROLSIGNAL I ~• • +lOV

~ I I-I - - - - - - - - - - - ovI II

AMULTIPLIEROUTPUT

BMULTIPLIER-------,

OUTPUT

SUM OFA&B

WITH "SOFT"SWITCHING

Fig. 9. Special effects "soft" switch.

Data Sheets-MC 1596 MC1496MC1595 MC1495MC1594 MC1494MC1545 MC1445MC1304, MC1305, MC1307MC1326, MC1328, MC1330MFC6040

ov

ov

ov

Address Information requests to:Edmund TynanSupervisor - Technical Informa

tion CenterMotorola Semiconductor Products

Inc.P.O. Box 20924Phoenix, Arizona 85036

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Solid State Rectifier StacksBy Guffy P. Wilkinson

How much did one hour and 39minutes of "Off Air" time costyour station last year?

How much money did your station spend for obsolete and expensive mercury vapor rectifier tubes?

How much did the money cost,which was tied up in spare rectifiertubes?

How much money was spent onuncomfortable engineering time toreplace bad rectifier tubes at 6 a.m.

Fig. 1. This 20 kV, 6 Amperestack replaces the 67:3.

44

How much money was wastedon power consumption for the rectifier filaments and for heaters andcooling devices for 6,370 hours?

Add up all this money and multiply it by the number of years ofyour transmitter life. That's a lotof money!

In the old days, mercury vaporand zenon gas filled diode rectifiertubes were the most efficient knownfor high power use. Mass-producedat relatively low cost, having littleinternal voltage drop and high current capability, they were the onlyanswer for rectifiers in large powersupplies for transmitters; nevertheless, they have many disadvantages.

The mercury vapor tube must beoperated within a limited temperature range, and the condensed mercury within it must be maintainedbetween 20º and 60º C. If theambient temperature is too cold,arc starvation occurs and the tubewill not fire, thus, some form ofheating is required. If the ambienttemperature is too hot, arc backswill occur and external cooling isnecessary. Spare tubes must be preheated for 30 minutes and maintained in a vertical position on theshelf. Thirty seconds of warm-uptime is required to bring the tubeup to temperature and this time islost if failure occurs.

Expensive filament transformersare necessary because of the highvoltage insulation required. Filaments bum out and spent emissionrequires tube replacement andcauses lost air time. Filament powerconsumption is costly and producesunneeded heat. Since no new equipment incorporates mercury vaportubes, fewer units are being manufactured, and they are becomingmore expensive and less reliabledue to extended shelf life. In manylocalities, they are very scarce andadditional spares must be boughtin order to guarantee availability.Today, the broadcast station still

operating equipment using mercurytubes is practicing a false economy,for new solid state rectifiers willpay their own way in a very shorttime.1t is now easy and economical

to directly replace mercury vaportubes with highly reliable controlledavalanche silicon rectifier stacks.These units plug directly into thetube socket; no re-wiring is necessary and the conversion takes onlyminutes. Such devices now have aservice history in excess of tenyears in power supplies of everyconceivable configuration.

Properly selected and protected,they will last virtually forever.They will operate in the temperature range of -65º to +100º C.They operate instantaneously anddo not require warm-up time. Filament transformers are unnecessaryand emission will not fade. Theydo not consume filament powerand produce no heat.

How It Stacks UpThe modern silicon stack is

composed of several individual controlled avalanche diodes stacked inseries in order to obtain the peakreverse voltage characteristic desired. This reverse voltage is thatwhich the stack must withstandwhen it is not conducting. A reasonable peak reverse voltage rating fora single junction diode is 1 kV.Thus, a stack rated at 18 kV PRVat 3 ampheres will incorporate 18I kV diodes in series, each havingan average current rating of 3 amperes.

Of prime importance in thisseries circuit is the requirementthat reverse voltage be dividedequally across all the junctions inthe stack. For this reason, the bestpractice is to match all the diodesin the stack for reverse currentleakage, and then shunt each diodewith a voltage dividing resistor and.a capacitor.

Nearly all individual diode failures result in a junction short,which reduces the PRV rating ofthe stack by the voltage rating ofthe diode. Because of this, a welldesigned stack will continue tooperate until its PRV rating is lowered below the PRV present, atwhich time all the rest of the diodeswill fail. To avoid this occurrence,silicon stacks should not be encapsulated so that individual diodes




Right on! Power tubes have come a ~ongway sincethe nostalgic days of EIMAC's first triode, the 150T. All theway up to the giant X-2159 developmental tetrode havinga plate dissipation of one and one-quarter megawatts.

The amazing X-2159 powerhouse can develop twomegawatts of CW power up to 30 MHz or so with up to17 decibels stage gain. It can also be used as a 60 kilovolt,1,000 ampere switch tube, or as an extremely hi.ghpower pulse modulator.

Two EIMAC X-2159s can be us sd in a 2.5 rnsqawatt, 100%plate modulated medium or shortw we trarsmit~er. At VLF,morever, two X-2159s can develop .+megawatts of CW power.

The X-2159 is a thought prove} ing example of EIMAC'scapability to produce tomorrow's tcbe today.

For full specifications on EIMAC's new

You've comealong waybaby.

super power tetrodeand other outstandingproducts write: EIMACDivision of Varian,301 Industrial Way,San Carlos, California94070. Or contact anyof the more than 30Varian/EIMAC ElectronTube and Device GroupSales Offices th roughout the world.

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December, 1971 45



]

Sl1IGl.E PHASE FULL WAVElllR10GEPAV 141.4'II. OF DC OUT PER RECTIFIERCURRENT 50'!1. Of DC! P£R Rs::TIFIER

SINGLE PHASE FULL WAVECENTER TAPPRV 314'!1. Of DC OUT PER RECTIFIERCURRENT SO'!I. OC! P£R RECTIFIER

3 PHASE HALFWAVEWYEPRV 2~'11. Of DC OUT PER RECTIFIERCURRENT 33.3 'II. OF OC! PER RECTIFIER

can be tested periodically and replaced if necessary.

This testing can be eliminatedby the installation of a neon lampacross each individual diode. Thereverse voltage on the diode lightsthe lamp and indicates that thediode is normal. If the diode shorts,or its reverse leakage exceeds thenorm, insufficient reverse voltage isdeveloped and the neon lamp isextinguished, automatically indicating a failure.

A voltage dropping resistor mustbe placed in series with the lampnot only to achieve the propervoltage for it, but to determine theamount of permissible reverse leakage possible before the lamp is extinguished. This self-testing featuresaves many hours of maintenancetime and because of their light,serve as an added reminder thathigh voltage is present.

When excessive reverse voltageis applied to a silicon junction, reverse current will start to avalanchethrough the junction at the mostvulnerable point on the junctionsurface. If the point passing thereverse current cannot dissipate thepower generated, the junction willbe punctured, thereby destroyingthe diode. A controlled avalanchedevice, however, controls the reverse current flow equally throughthe whole surface of the junction;therefore, more power can be dissipated before the junction is destroyed. This provides added protection for the diode and is a verynecessary feature in a silicon stackto combat high voltage transients.

The only disadvantage that a silicon stack exhibits' in comparison tothe mercury vapor or zenon gasfilled tube is its destruction due to

46

3 PHASE FULL ~ BRIDGEPRV P£R RECTIFIER IOS 'II.OF DCPER RECTIFIERCUllRENT 33.3 'II. Of OC1 PER RB:TlflER

excessive voltages caused by transients or lightning. However, ifadequate safety factors and goodengineering practices are observed,this condition will rarely occur.

Most overvoltage is caused byhigh voltage transients or lightningon AC power lines. Line SurgeProtectors, however, are now available to control lightning and suchhigh voltage transients. For lightning protection, these devices areplaced on the load side of the inputbreaker between the AC line andground. This is done since lightning generally strikes all phases atthe same time, and, therefore, thevoltage differential is developed between line to ground rather thanfrom phase to phase. When transients occur from other sources thatare developed between phases, thenit is practical to install an additionalLine Surge Protector across eachphase.

The most practical Line SurgeProtectors incorporate thyrite varistors which are voltage sensitivevariable resistors. The varistor hasa given resistance at its ratedvoltage; and at its rated voltage,very little power is dissipated. Theunique characteristic of the varistoris that when voltage increases, theresistance of the varistor decreasesat a much greater rate than thatof the voltage increase. Thus, thevaristor acts as an instant load toany overvoltage and is an automatic, instantaneous regulator forsuch overvoltage.

High voltage transients are alsoproduced by the collapsing field ofthe filter reactor in a power supply. The filter reactor produces amagnetic field around itself havinga force equivaíent to the power

being generated at any given instant. When the equipment isturned off, the field collapses, generating a voltage transient manytimes that of the normal peak reverse voltage. When mercury vaportubes are used, this voltage causesan arc back in the tube which isnot seen because the tube is notoperating, but such a transientwould destroy a silicon rectifier. Itis very simple to filter out thisspike with the installation of anRC filter network from the rectifier side of the filter reactor toground. The formula for determining the value of the resistor andcapacitor is:

R=EDC1DC

C = LI 2 de X 1Oº4 E2 de

Where resistance is ohms, C isin microfarads, Ide is the totalDC current drawn, and L is thetotal inductance in the circuit.The voltage rating of the capacitor should be DC voltage divided by .7 (approx.) and a 50 Wattresistor is normally sufficient.A well-designed silicon stack

should have a reverse voltage rating of at least 200 percent of thatto which it is normally subjected.The current rating should be atleast 300 percent of average current. This will assure an adequatesafety margin under nearly all circumstances.

Proper Stack SelectionTo select the proper silicon

stack replacement for a given tube,the circuit should be analyzed toprovide the proper safety margin.

Figure 1 shows the four mostcommonly used rectifier circuits,the percentage of peak reverse voltage present for each stack withinthat type of circuit, as well as percentage of total current that eachstack will supply. For example, ina single phase full wave center tapcircuit, the peak inverse voltage is314 percent of the rated DC voltage; and each stack will supply 50percent of the current. Therefore,if two mercury vapor tubes wereused in a 2800V, 1 ampere supply,each stack would be subjected to anormal peak reverse voltage of8,792V, and each stack would supply 500 mills. In this instance, the




Turnover Would Create Chaos

Evans Outlines Renewal TasksMark Evans, chairman of the National Association

of Broadcasters' Task Force on License Renewals,warned broadcast executives that they must bandtogether and fight unjust attempts to deprive them oftheir licenses or face the possibility of losing them tothose who "promise to produce programs more satisfactory to the Commission's taste."

He said the effort of the NAB Task Force neverwill succeed unless each broadcaster maximizes"every ounce of power and influence this industrypossesses to achieve a fair and reasonable licenserenewal policy."

Evans, vice president and director of public affairs.Metromedia. Washington, emphasized at NAB'sChicago Fall Conference that broadcasters are notattempting to escape their responsibilities, nor "seeking to avoid our commitment to operate in the publicirterest by one iota," but are seeking "a balancedrecognition of everybody's rights and not the myopicpursuit of one group's rights."

He noted that NAB's Board of Directors feels thefinal solution to the license renewal matter will be afederal law spelling out a permanent national policybinding on the Federal Communications Commissionand the courts.

Broadcasters. Evans said. are up against a "Coor-

dinated inter-locking national movement to displacecurrent licenses." This movement, he stated, isfinanced by a war chest of over a half-million dollars.

He said that while broadcasters are united againstthe unjustified harassment by radical groups seekingtheir licenses, they also must be united behind whatever bill is drawn up for Congressional action.The fight can be won, Evans said, because "right is

on our side. The wholesale turnover of radio and television licenses to challengers would create chaos andpublic resentment that would make it very uncomfortable for those who support it."To combat the campaign by radical groups, Evans

urged broadcasters to:- Master the facts and be articulate on the arguments.

- Sell their position to everybody: employees,family, clients, advertising agencies, serviceclubs and public service organizations.

- Establish "eyeball contact" with their Congressmen. "Letter writing is not enough."

- Fight the label "racist." He said "the only thingracist about our efforts is the people who aremaking it so in their criticism."

-A void the wheel-spinning of futile legislativeefforts.

-Stand by for an all-out battle on the issue.

Voice Identification Still Applies To Land MobileIn response to requests by the Associated Public

Safety Communications Officers, Inc. (APCO), andRY DAX. lnc., for reconsideration of rules governingoperation of non-voice radio systems on voice channels in the land mobile services below 950 MHz(Docket 19086), the Commission has retained arequirement for identification of land mobile radiostations by voice, but has deleted a requirement forautomatic sensing of channel occupancy.

In an order adopted August 18, 1971, the Commission amended Parts 89, 91 and 93 of the rules to permitregular and expanded operation of non-voice operation in the land mobile services.

APCO had asked for an exception to the requirement for station identification by voice to allow stationidentification by Morse Code and RY DAX had askedfor deletion of the requirement that non-voice systemsennploy automatic sensing or monitoring equipmentthat can prevent transmission on an occupied channel.The Commission said, in denying the APCO

request, that use of Morse Code would not affordsignificant advantages and noted that the additional

December, 1971

transmitting time required could increase potentialinterference.

In granting the RYDAX request, the Commissionstated that it had originally required automatic sensingof channel occupancy to protect voice communications from interference by non-voice transmissionsand to assure that non-voice operations would besecondary to voice operations.The FCC observed, however, that RYDAX, as

well as General Electric Company and RCA Corporation, had raised "significant questions" as to theeffectiveness and adaptability of automatic sensingdevices and said that while it would permit use ofthese devices, it would not impose a mandatoryrequirement for their utilization at this time.

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stack should be rated at 18 kV, 1.5amperes.It is very important that silicon

stacks essentially developed to replace a given tube should be ratedwell in excess of the tube in orderto avoid failure. Several 1 kW AMtransmitters use two 8008 or 872tubes in a full wave center tapcircuit providing 2800 Volts DC at1 amp. These tubes are rated for amaximum PRV of 10 kV whenoperating between 20º and 40° cand in this instance, very littlemargin of safety exists. If a siliconstack with a PRV of only 10 kVis used, then it would be destroyedimmediately by a 1O percent linevoltage variation or a no-load condition which increases the highvoltage.

When silicon stacks having 300percent safety factor are used, little or no heat is generated. If heaters of blowers were used to keepthe tubes at the correct temperature, they may be removed.

Some broadcast equipment hasbeen designed incorporating parallelrectifiers for greater current capability. Such parallel operation

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December, 1971

with silicon rectifiers must beavoided and is unnecessary since asingle silicon stack can be providedwith any current capability desired.

The voltage drop across a siliconstack is approximately the same asthat of the mercury vapor tube;therefore, the rectified voltage willbe the same. This is not the casewhere high vacuum rectifiers arereplaced. When replacing 5U4'sand 5R4's, the silicon unit will produce up to 15 percent more voltageand this should be taken into consideration.

Several station engineers haveattempted to build medium currentsilicon stacks in an effort to reducethe cost of conversion to solid staterectification. It is very rare thatreduced cost was achieved and inmany instances, complete failureresulted. Failure most often occurred because low cost, poor quality diodes were purchased.

Unless adequate means wereavailable to properly test these devices, the engineer had no way ofknowing actually what he purchased or why they failed. Experience with several sample purchases

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of so called 1 kV, 6 ampere devicesfrom several processing jobbersproved that less than 20 percentof the diodes could withstand aDC voltage of 1 kV, and the reverse leakage of these varied from10 MA to 500 MA. Placed in astack, every one of them failed.

Acceptable diodes such as theIR 6F100A on the Syntron D-140-AS, 1 kV, 6 ampere unmatcheddevices are priced at around $11each in quantities of 1 to 99. Thereverse leakage on these units canvary up to 10 MA but should beselected not to exceed 5 microamperes at rated PRV. A stack of20 of these rectifiers would certainly cost the station trying tobuild it far more than $200, forin addition to the diodes, heatsinks, resistors and capacitors mustbe acquired and a mechanicalmeans of support must be obtained.

The Diode As ATransient Suppressor

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47



Digital logic basicspart 3 of a four-part series

By E. S. Busby, Jr.*

• Ordinary two-state logic concerns itself with one wire at a timeand is fine for yielding the answersto yes/no, true/false, on/off,whether or not, etc. An array ofwires can be used to define "howmany" and "how much". Twowires, each of which has two possible states, have 2 X 2, or 4 possible arrangements. Add one morewire and there are twice again asmany possibilities. If there are Nwires there are 2N different arrangements of ons and offs amongthem.

If the wires and their states arenamed in a way everyone understands then the states of a numberof wires can define "how many".

Imagine a wire that can have tendifferent states (ten voltages, perhaps). Each state has a name,called a numeral, running fromzero through. nine. Each wire has aname, called its "weight", there areunits (1Oº), tens (101), hundreds(1O'), thousands (1O"), and so on.Thus, as we are all taught, when8092 is written we know that thereare:

2 many units-s-Z X 19 many tens=9 X 10no hundreds-e-O X 100

and 8 many thousands-e S X 1000This scheme (the decimal sys

tem) for counting things is used bypeople with 1O fingers, gears with10 teeth, and stepping relays with10 contacts. They all work slowly.Wires with 1O states are more trouble than they are worth. Wireswith two states we have. So, tomake use of two state wires, therecame to be a "binary" numberingsystem. At the risk of creatingsome confusion, two well-knownnumerals were borrowed to namethe two states. They are zero (O)and one (1). To add to the confusion the names of the wires (the*Engineer, Ampex corporation,Redwood City, Calif.

48

weights) were also borrowed fromthe decimal system. These namesare units, twos, fours, eights, sixteens, etc., the mutiples of two.

One And One Are 1OThe binary system (as well as

some others) are taught to the kidsin school these days. To them111101 means:A unitno twoA fourAn eightA sixteenA thirty-two

1o48

1632

TOTAL = 61

You think in decimals. Much oftoday's equipment operates in binary. To do the translation between systems in your head, it isadvisable to commit to memory thefirst 12 multiples of two:

1 = 2º 128 = 27

2 = 21 256 = 2"4 = 22 512 = 2º8 = 2ª 1024 = 21º

16 = 2'' 2048 = 21132 = 2· 4096 = 212

64 = 2ºTo convert from binary to deci

mal, for example 100111, first examine the right-most "place" or"bit". If it is a 1, then there is aONE involved, so add it in. If thenext to the left is a 1, then a TWO

INPiJL

ATMSIU'l'.., ..... lAfl0ntf:l5Tt0Uf1l

•••. I*···· linc ...l)TH. .•..•... l•...... lI .I... ········"t ..... H."IIu."u.,..

Fig. 1 Four-bit binary counter.

.II2'1·).••l·S•o?·••·1•1•1.l•l·t•·1·»l•l•l•I\1•4·1?l•••l·U•·••1·1•1q•1•1·1s

_ILINPUT

COUNTS O OO O TO 1001 ININD IN Bl NARY MANNERAT 1010 ITENl GATE''G'' REACTS, RESETTING B & OINVERTERS "I" PROVJOEDELAY TO INSURE RESETTINGRESET DURATION CAN BE INCREASED BY CAPACITORS

NOTE:AS TEXT EXPLAINS, THIS ANO FOLLOWING CIRCUITSWIUHAVf INPUT ON LEFT. WHILE NUMBERS IN CAPTIONSANO TEXT wtu, HAVE SMALLEST BIT RIGHT-MOST.

Fig. 2 Example of partial decoding, including reset.




is involved, so add it in. If the nextto the left is a 1, add in a FOUR,etc. In the example shown there isa ONE, a TWO, a FOUR, anda THIRTY-TWO represented, fora total of 39.

To convert from decimal to binary, for example 525, ask yourself: "Which is the largest multipleof two which isn't larger than 525?"512 fits, so write a "1" in the 512column. 525 minus 512 leaves 13unaccounted for. The largest multiple not larger than 13 is 8, so a"l" goes in the 8 column. Thisleaves 5 unaccounted for, so a "1"goes into the 4 column, leaving a"1" in the 1 column. Write zeroesin all other columns. Result:

1 o o o o o l 1 o 1 ~ 525

Figure 1 shows how the outputsof cascaded flip-flops directly reveal the (binary) number of inputedges received. In the exampleshown, the sixteenth input edge returned the counter to its startingposition. The counter exceeded itscapacity or "overflowed" at sixteen.Counters which overflow at an exact multiple of two are known as"pure binary". Counters can be arranged by feedback from laterstages to earlier ones so that theycount in a binary fashion, but return to zero prematurely.

One popular compromise between the decimal world with its1O-fingered people and the binarydevices with their two states is thebinary counter which returns tozero on the 10th count. Six of thepossible 16 states are not used. A4-bit binary "word" which neverexceeds the range 0000 through1001 (O through 9) is called BCD,or "Binary Coded Decimal".

This scheme for representingdecimal numerals is used a greatdeal where people enter numbersinto a system (with a keyboard forexample) or where decimal numerals must be displayed or printed. Itis not so much used in computation. There are BCD counters, BCD

December, 1971

decoders and BCD/binary and binary /BCD converters. Most demimal numeric displays use a BCDinput. Besides the popular 8-4-2-1binary weighting there is a largenumber of other weighting schemesusing 4 bits to describe the set of1O decimal numerals. (More aboutthese next month.)

Look at Figure 1 again. Theschematic is odd in that the inputis at the right instead of the left, asis usual. This was done to avoid apopular source of confusion. Incounters, the units output is the onenearest the input, and in left-toright circuit diagrams the units or"least significant" output is the leftmost. When writing numbers, it iscustomary to place the least significant bit right-most. You shouldlearn to visualize binary numbersarranged either right-to-left or left-

to-right. To force you to do this, inthis and the next article, circuit diagrams will be arranged with inputson the left, and numbers will bearranged with the units columnright-most.

Pick A NumberTo know when a counter con

tains some particular number, it isnecessary to "examine" all thestages of the counter to see if thatnumber's unique arrangement ofhighs and lows exists. Convert thedesired number into binary form.Keeping in mind that the unit column is the one nearest the counting input, figure which stagesshould have high (1) outputs andwhich should have low (0) outputs.Connect an input of an "AND''gate to the regular output of eachstage which should be "ONE" and

.n.INPUT

Fig. 3 Down-counter (binary).

~!AtlAITUISICOUlll'......

""'™.'I'.u

"".."..

J1WHEN"CP" IS HIGH: STAGEA IS PERMtnEDTO'10CGL("

STAGEBIS PERMITTEDTO '10GGU" AFTERODDNUMBERSSTAGE C IS PERMITTED TO '10GGLE" AFTER OOll ITHRW, 0111 tSCVENl, 1011 IELEVEM ANO 1111 IFIFTEENlSTAGE O IS PERM ITIED TO ''TOGGLE" AFTER Dill tSEVENI ANO ill Ill FIFTEEN

ANY COUNTERWITH CLOCK INPUTS All COMMON IS SYNCHRONOUS

Fig. 4 Synchronous binary counter.

49



INPUT NO. "A"

8

8INPUT NO. "B"

NOTEl.

OUTPUTOF EXCLUSIVE ORGATE IS LOW IF INPUTS ARETHE SAME (H-H OR L-Ll ANDHIGH WHEN INPUTS AREDIFFERENT

NOTE2. DO - IT - YOURSELFEXCLUSIVE OR GATE

Fig. 5 Simple four-bit comparator.

to the inverted output of each stagewhich should be "ZERO." Thisway all the inputs to the AND gatewill be high when the desired number has been counted. No othercount can produce this result. Thisprocess is called "decoding" acount. As many decoding gates maybe attached as there are differentnumbers to be decoded.

Partial DecodingOften a counter is reset to zero

as soon as some desired count isreached. In this case it is perrnissable to examine only the stageswhich should be active (1) at thedesired count. To decode 525, forexample, requires only the four-input gate attached to the 512, 8, 4,and 1 stages. If the counter werepermitted to count beyond 525,false outputs would appear at 541,

50

557, 573, etc., but if resetting occurs right after 525 there is noproblem.

Sometimes It PaysTo Wait

Using the output of a decodinggate directly to reset a counter cancause what is called a "race" condition. This effect is often encountered in logic circuits where the detection of something is used to undo the very thing that was detected.In a counter the danger is that onestage will reset faster than anotherand thereby negate the resetting signal before all stages get reset.

Adding delay between the gateand the resetting terminals, as inFigure 2, will usually assure resetting. Adding capacitors will furtherlengthen the reset period, maybeeven to the point that it's long

enough to see on a scope.Figure 2 happens to be a BCD

counter. It counts from 0000 (zero)through 1001 (nine) in a binarymanner. On the tenth count (1010).the partial decoding gate reacts andquickly resets the second and fourthstages to zero.

Cape Kennedy ConnectionMost counters "increment" (get

one bigger) for each input count.Figure 3 shows how a counter canbe arranged to "count down" ordecrement one for each input edge.The difference is that a countingedge is passed to the next stagewhen the output changes from O to1 instead of the other way around.

In the counters discussed so far,the stages were connected in cascade. Such counters are called "ripple counters" and suffer from twolimitations. The fastest speed atwhich recognizable counting canoccur is limited by the total delaytime through all the stages. Try togo any faster, and the first stage isreacting to an input before the previous count has rippled all the wayto the output.

Even when counting slowly, ripple counters are prone to producing"decoding spikes" at decoding gateoutputs. You might think that thereception of the eighth count mightlook like this: FROM: 0111

TO. 1000It doesn't. It looks like this: 0111

THEN: 0110THEN: 0100THEN: 0000THEN: 1000

with the "rippling" going from rightto left in the example. A decodinggate set for zero, four or six wouldproduce a short, but troublesomeoutput during the transition.

Figure 4 illustrates a synchronous counter. The counting inputsof all flip-flops are fed from a common source. The steering inputs,which determine whether or not theflip-flop will flip at clock edge time,are connected, using gates, to theprevious stages. Outputs can onlychange at clock edge time, andwhen several stages are changing atonce, they all do it together.




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December, 1971 51



Speed is limited by the delay ofone flip-flop and the gate delays.Decoding spikes are drastically reduced if not eliminated.

When not counting at high frequencies and when using partial decoding and resetting, a ripple counter is as good as any. Otherwise,synchronous counters are preferable.

Following, stated somewhattersely, are some approaches usingcounters to answer questions andsolve problems:l. HOW MANY?

Start the counter at zero.Make edges out of the events tobe counted. When you get curious, examine the counter outputs. Convert these output statesfrom binary (or perhaps BCD) todecimal and there's the answer.2. HOW FAST?

Start the counter at zero andcount input events. Allow thecounter to proceed for exactlysome known length of time, likeone second. (This may take yetanother counter.) The number inthe counter is then events persecond.

4A

Fig. 6 Full comparator.

52

3. HOW LONG?Start the counter at zero.

Make edges at some known frequency, like 1 megacycle. Startthe counter when one input eventis received, and stop it when thenext arrives. The number ofcounts is the period of or "timebetween" the events.4. IS "A" EQUAL TO "B"?

See Figure 5, which showsthe simplest of comparators. It isessentially an adjustable decoding gate.

Figure 6 shows a more complex comparator. It has threeoutputs, one of which is alwaysactive. It reveals whether thecounter number is less than,equal to, or greater than thecomparator's other input.5. IS "A" FASTER THAN

"B"?If an "A" arrives, count up

one. If a "B" arrives, countdown one. If both arrive atonce, do nothing. If the counterreaches its maximum value, stopcounting "A''s. If it reaches itsminimum value (zero) stopcounting "B"s.

If the counter hangs up at themaximum value, A is faster thanB. If it hangs up at zero, B isfaster than A.

This up/down counter approach is often used as a frequency /phase comparator. Whenused to phase-lock a local oscillator to some reference input, thefiltered output of the counter'smost significant stage is used tocontrol the local oscillator's frequency. Phase-lock is indicatedby the most significant stageturning on about half the time.An exact 50 percent duty cycleindicates that the two inputs areexactly 90° apart.

Words Of WarningWhen measuring time and fre

quency you cannot usually predictwhether you started and stoppedthe counter just before a count orjust after one, leaving an inherentuncertainty of + 1 count.

When measuring that which liesbetween events, like the length oftape between N frame pulses, or thelength of wire between N telephonepoles, don't forget that the first

NOTE:>MEANS "GREATERTHAN"

IF 8A IS UNLIKE 8B, ALL FOLLOWINGSTAGESARE INHIBITED.

IF 8A IS LIKE 8B, THEN 4A + 4BGETTOCONTROLTHE OUTPUT.IF 8A = 8B AND 4A = 4B, THEN2A & 2B GETTODO IT •. AND SOON




phone pole counts one before anywire goes by. For these and similarproblems, remember to subtract onefrom the total count.

Put it this way: If you walk fourblocks .. you touch five comers. Thecounter counts corners.

When starting and stoppingcounters, it is best to avoid gatingthe input signal on and off. Instead,manipulate the first stage's steeringinputs. If the input happened to beactive when you shut off the inputgate, an extra count would result atshut-off. If you must gate the input,it is best to make narrow pulsesout of the events to be counted.

Counters and the circuits whichare often hung onto them wereamong the first to undergo mediumscale integration (MSI). MSI devices generally cost about the same,maybe a little less, use a little lesspower and occupy much less realestate than the equivalent made outof separate flip-flops and gates.There are MSI synchronous andripple counters in BCD, decimal,and 12 count. Some count up anddown. Almost all have four stages.

MSI decoders typically have oneoutput for each possible input pattern, with only one output active ata time. Some can withstand the ignition voltage of gas-discharge numeric display tubes. Others can energize more than one output at atime and can switch the currentsused by the incandescent lamps ofseven-segment numeric displays.Several 5-bit comparators are available. These have three outputs available: A greater than B, B greaterthan A, and A equals B. Four-bitbinary adders and subtractors areavailable (more about this nextmonth). Most MSI devices areTTL.

New MSI devices appear on themarket at a frightening pace. Readthe ads and don't rely on out-ofdate catalogs.

How Much?Some of the variables of life are

already "quantitized". Your paycheck, when and if it changes, mustchange by at least one cent, thesmallest increment, or some wholenumber times one cent. Money isexpressed as a number anyway, soHOW MUCH MONEY reallymeans HOW MANY CENTS.

December, 1971

8V

L• 7TO 8R

L•6T08

>5R

I_g

~ R~ r~ >4H· 4 TO 8

J J JI ' 4INPUT

W MAX

~>3R

R

>1 L• 1 TO 2R

R

A~ • VOLTAGECOMPARATOR

B~A IS MORE POSITIVE THAN B.THE OUTPUT IS HIGH

Fig. 7a A three-bit (8 level) A/D converter. No counting is involved.

_íl_CLOCK

ANALOG INPUT

+MEANS INPUT IS GREATERTHAN O/A'S DC

DIGITAL TO ANALOGCONVERTER

:lO~gUT

1 J~--4l~l'----c:~ WORD

GO.rr-1----e---o

CONTROL

BI NARY COUNTERRESET PERMIT

Fig. 7b Counter-type AID conversion.

53



The words in the dictionary differ by at least one whole letter.There is no such thing as half-waybetween "card" and "care". Mostgoods have some minimum quantity, a division of which does notexist or is not important. So thereis a stick of gum, a jigger of whiskey, a page, a word, a grain ofsand, and "one each" soldier. Thequantity of these usually consists infinding how MANY.

Other variables, such as temperature, pressure, brightness, weight,etc. may be measured in terms ofsome standardized unit like seconds, degrees, grams, centimeters,etc. HOW MUCH TIME then becomes HOW MANY SECONDS(or milli-seconds, or microseconds.)It is up to you to decide what isthe smallest increment of interest.Even if you are fussy, there is nopoint in being interested in an in-

+12V

+4.4

8.75K

+4.4 .8mA +4.4

OUTPUT

RL O.lmAPERINCREMENT

8

BINARY-WEIGHTED CURRENT SOURCESDIFFERENT CURRENT LEVELS MAKE EXACTCURRENTS DIFFICULT TO GET

+12V

8.75K 8.75K 8. 75K

+4.4 +4.4

8.75K

+4.4 +4.4

R R OUTPUT

<(E-e-R

.4mA .2mA .lmA

<(

2R<: ~ 2R~ ~<(

R ~ §

.lmA PERINCREMENT

4 8

EQUAL CURRENT SOURCES WITH LADDER ATIENUATOR.CURRENTS SHOWN FOROOOl. AT EACH RESISTOR JUNCTIONBETWEEN SOURCE AND OUTAJ T; CURRENT SPLITS EQUALLYTWO WAYS. ONE WAY GOES TOWARD OUTPUT, THE OTHERDOESN'T.SMALLER SPAN OF CURRENTS AND RESISTORVALUES AIDS ACCURACY.

Fig. 8 DI A converters. In the examples shown, current is taken from the emitter viathe diode when the bit is inactive (low).

54

crement smaller than the accuracyof the measuring device, nor in anincrement so small it is obscured bynoise.

Whereas sticks of gum arecounted, temperature and pressureare measured. It is often handy toconvert one of these continuouslyvariable quantities into a voltage.For this there are numerous transducers like microphones, photoelectric cells, strain gauges, etc. It issometimes even handier to convertor quantitize the variable voltageinto an electrical number. In thisform, the variable may be displayed(as a number instead of a meterdeflection) or massaged by a computer.

Converting a variable voltageinto a numeric quantity is the job ofan Analog-to-Digital (A/D) converter. The size of the number thatmust be used depends on the smallest increment of interest and themaximum range of the variable.The unit "bit" must represent aquantity not larger than the smallest increment, and the number of"bit" must be enough to allow forthe maximum variable value.

Thus, to qauntitize the outdoortemperature from -40ºC to +60°c to the nearest tenth degree, youmust accommodate l 000 differenttemperatures. 10 binary "bits" have1024 combinations, so a 1O-bit binary number is adequate.There are more methods of A/D

conversion than there is room todescribe, but generally they taketwo forms:

l. Using a massive resistive volttage divider "ladder", with avoltage comparator at each rungof the ladder, find out whichrung's voltage is equalled or justexceeded by the input variablevoltage. Convert this "rank" intoa binary number. This methodhas the advantage of speed inthat the output number is determined in one go. It requires lotsof hardware, however.

2. The outputs of a counter areconnected to a D/ A (Digital-toAnalog) converter, whose outputis then compared (in a singlecomparator) to the input variable




voltage. Any time an A/D conversion is desired, start the counter from zero and let it countuntil the D/ A output just exceeds the input variable, thenstop. The number in the counteris the desired conversion.

It takes time to do the counting, and this is a disadvantageof this approach. It tends to useless hardware, however, and besides the D/ A part can often beused to advantage elsewhere inthe system.Figure 7 shows, in very simple

form, two D/ A approaches. Figure8 shows two popular DI A approches. Remember that a D/ Aoutput is not truly an analog output. It cannot vary continuously,but: only in steps. It is thereforea "dedigitized" voltage.

Both DI A and A/D convertersshould have an accuracy of at leastlh a basic increment. Thus when adigital number makes that one-stepchange from 011111111 to 10000-0000, the output voltage really doesgo up by at least lh a notch, andno more than 11h notches.

Once a quantity is made into anelectrical number, whether bycounting, keyboard entry, thumbwheel switches, or A/D conversion,there are some digital techniquesthat make the whole process worththe effort. That's the subject fornext month's article. .&

Recommended Readingl. DIGITAL ELECTRONICS

WITH ENGINEERING APPLICATIONS, Thomas P. Sifferlen and Vartan Vartanian.Prentis-Hall, 1970. Chapters 4,6, 7.

z. DESIGNING WITH MSI, Vol.I, "Counters and Shift Registers," by Les Brock. Pub. bySignetics Corp.

3. HOW TO USE SHAFT ENCODERS, Pub. by DATEXDiv. of Conrac Corp.

4. HOW TO USE INTEGRATEDCIRCUIT LOGIC ELEMENTS, Jack Streater. Pub. byH. W. Sams (Cat :f:/:20755).

December, 1971

5. DIGITAL COMPUTERSSTORAGE AND LOGIC CIRCUITRY, Chapt. 6. Pub. by H.W. Sams (Cat. :f:/:20131)

6. ANALOG AND DIGITALCOMPUTERS - ORGANIZATION, PROGRAMMINGAND MAINTENANCE. Chapter 6. Pub. by H. W. Sams (Cat.:f:/:20132)

7. SOLID STATE COMPUTERCIRCUITRY. Chapt. 8. Pub. byH. W. Sams (Cat. :f:/:20133)

8. Fairchild Application Notes:APP-119, "Ways to increase

speed in Large-CountBinary Counters",Jack Irwin.

APP-120, "Using the J-K FlipFlop in Small Module Counters", JackIrwin.

APP-160, "Applications of theCCSL 9301 Decoder", R. CliveGhest.

APP-164 "Applications of theftA722 1O-bit Current Source", M. Rudin, G. Erdi, R.Walker and R. Ricks.

APP-169 "CCSL 9306 UpDown BCD Counter", R. Clive Ghest.

APP-170 "Applications of the9311 One-out-ofSixteen Decoder".

9. Signetics Application Memos:"Binary to BCD Converter", J.Becher."Self-Correcting Ring Counters", Tom McCarthy"321 Dual J-K Binary Applications", Robert Juan."Up-Down Binary Counters",Joe Becher."TV Sync Generators", JoeBecher."Television Pattern Generator",R. Seymour."High Voltage Decoders withConventional Elements", DaleMrazek.

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Transient SuppressionA recent contributor to "Letters

to the Editor", taking issue withan article on "Automatic Assistance Circuits" in a previous issueof Broadcast Engineering, raiseda question that may remain unsettled in the minds of many readers.Perhaps we can settle it here.The original article touched upon

transient suppression in DC control circuits. It suggested a reverseconnected diode across a relay coil,as shown in Figure I, to shunt outthe inductive "kickback", or transient, that occurs when switch Sis opened.

Arguing with this line of reasoning, the" Letters" contributor countered with, "Actually, the transientvoltage is of the same polarity asthe applied DC and it is the Zener

breakdown characteristic of thediode that limits the voltage of thetransient." Is this true?

My off-the-top-of-my-head reaction was one of consternation. Ihad just wired a 24-volt relayswitching control center for a largeindustrial sound installation. Fortransient suppression on its 20-oddrelays, I had used inexpensivediodes with a PI V rating of 1000volts. Clearly, their Zener actionwould not come into play at reasonable voltages' Transients spikingat 1000 volts are guaranteed to beheard in adjacent audio circuits.Had I been laboring under a falsepremise?With doubts thus raised, I went

back to review a few fundamentals.If you, too, are so far removed

Cartridge Tape Splice FinderAt WIOD we built a simple,

inexpensive and easily built splicefinder. It uses a photo electric celland is installed on an elderly Cartritape 2 playback machine, usedprimarily for cueing cartridges justbeyond the splice. It can be builtaboard your regular recorder, butthere's more flexibility in having iton another machine because youcan splice cue cartridges whiledoing production work on yourregular makeup machine.

Loads are so slight that it canbe readily powered from withinthe unit it is installed on. Of coursesome component values wouldhave to be changed if the unit isother than a Cartritape 2.

The electronics (not includingthe PE cell and exciter lamp) areaboard a small angle plate attachedto the tape deck with two selftappers that could be black boxedcompletely external to the machine.The PE cell, with the lamp taped

one half to three quarters of aninch behind the eye, will probablyscan the passing tape from a distance of ~ to \/,¡ inch. Its small

56

mounting bracket could be fixedto the deck with contact cement ifdrilling is undesirable.

It's possible to adjust the sensitivity of the PE cell to see theactual splice, but a bright foil is amuch better idea for it is morepositive and allows exact adjust-

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ment of sensitivity. Put a half inchslug of bright foil atop the splicefor the PE cell to see. 3M # 51pressure sensitive 7132 sensing tapeis one type that works well. Thisis a conductive foil but its conductivity is not the requisite- brightness is the only requirement.

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from your exposure to the basicsas to be a little uncertain aboutinductive "kickback", maybe youcan profit from my research.

First, it is important to agree thatwe are dealing with an inductivephenomenon. The many turns ofwire in a relay coil, surrounding aniron core, possess appreciablesc(f-inductance. The distributed capacitance of these turns is relativelysmall, being inconsequential whenworking with DC and low frequency AC. Resistance of the wiremay be appreciable but- being bydefinition nonreactive- it cannotcontribute to the generation oftransient voltages and currents.Thus the principal factor at work isthe coil's inductance.

s

Figure 1

~o +e¡

Figure 2

When the excitation voltage isremoved from a relay coil, the resulting collapse of the magneticfield in its core induces a voltage,or counter-electromotive force(cerní) that tries to maintain thecurrent in the coil. This followsfrom the fundamental characteristicof an inductance: self-inductanceis that property of an electric circuit that opposes any change inthe current in that circuit.

Expressed mathematically for aninductance,

dicemf= -L dt 'where cemf= instantaneous volt

age generated by thecoil,

i =instantaneous current in the coil,(Continued on page 58)




Engineer's Exchange(Continued from page 56)

t =timedi . fcrt= instantaneous rate o

current changeand L =value of inductance:

a constant for a particular coil.

This means that the polarity ofvoltage that appears across theterminals of a relay coil is determined by the direction of the current through it. This voltage mayundergo any change necessary tomaintain the current. To examinethis relationship a practical stepat a time, first consider Figure 2.With switch S initially open, instantaneous voltage e across thecoil is zero, as is the circuit's instantaneous current i. Since thereis no current. there is no dropacross resistor R and the voltageat A (referred to ground)=the voltage at B=zero.

Now we close S. At this veryinstant, i remains at zero (an inductance opposes any change in current). This means that the voltageat A still equals the voltage at 8,

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58

because there is no iR drop acrossR. However, A now clearly standsat voltage E above ground, whichmeans that point B must also. Inother words, the coil's cemf e isof magnitude E and of the samepolarity, as indicated in Figure 2.

Having thus established that theinduced voltage is of the samepolarity as the applied voltage atturn-on, we'll pursue its nature atturn-off. For this, refer to Figure 3.

Assume that switch S2 has beenclosed for some time, so that asteady current I is flowing. (If Lwere theoretically perfect, withzero resistance, the steady-statecurrent with S2 closed would belimited only by the battery's resistance. Rb is included here to permita finite current.) Suppose

Rb= I ohm, andE= IO volts. ThenI= 10 amperes.

The nature of inductance dictatesthat, at the instant S2 is opened, Imust momentarily remain at 10amperes. This is true regardless ofthe value of R. Then if R is 100ohms, there must be an instantaneous voltage developed across it of

IR= IOOOvolts.

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Since the direction of currentremains unchanged (the inductancegenerates a voltage that opposescurrent change), this IR drop mustbe positive at A with respect to B.But A is 9 volts positive with respect to ground (E-1 Rb), so thecoil's cemf e is 991 volts negativewith respect to ground. This is thepolarity indicated in Figure 3.

+

Figure 3

This shows that a diode connected across the coil as in Figure 1will indeed conduct in its forwarddirection when the relay is deenergized, limiting turn-off transient voltages to very low values.The Zener breakdown voltage isnot a consideration in its operation.

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A possible source of confusionin dealing with polarities lies inthe source of voltage. When thecoil's current is supplied by an external battery and a steady stateis reached, current flows throughthe coil from positive to negativejust as it would in a resistor. However, when the external circuit isopened, the coil becomes a gencrator. and the int crnal current inany generator supplying energy toa circuit flows from negative topositive (note the direction of Ithrough the battery in Figure 3).

Diode suppression is a convenient way to obtain noise-free relayoperation in DC control circuits.However, there is a trade-off tokeep in mind: The result of limitingtransient voltage rise is a prolonging of the decay of current in therelay coil. This effectively delaysthe opening of the relay by a substantial interval. Fortunately, inmost control circuits it isn't important whether a relay opens inthree milliseconds or in 75. Onthe other hand. such delayed release is intentionally incorporatedinto some telephone switch-gearcircuits to time the sequence ofrelay operation.

And to conclude with a parent het ica 1 observation, the diodesuppressed relay control circuitthat I built has since proven to befree of audio transients.

R. H. CoddingtonRichmond, Va.

For further lnform•llon. circle d•hIdentification number on reader service card.

100. ANACONDA WIRE ANDCABLE CO.-Voice frequencysubscriber loop design principlesare described in detail in a newengineering bulletin. The 68-pagebulletin en t i tled, "Principles of

Voice Frequency Subscriber LoopDesign", is used in conjunction withtwo subscriber line calculatorsshowing the most economical combination of gauges, for a given

(Continued on page 60)


Substituting The 684The nearly extinct 6B4 (VJ 1)

tube in the fine old 1181-A frequency monitor can easily be replaced with the relatively modern6W6GT. Simply leave the presentleads connected to Vl 1 socket andjumper from pin 2 to 8, also frompin 3 to 4. After this modificationeither a 6B4 or a 6W6GT tubemay be used in Vl 1 socket. Noother changes are necessary, justcheck B+ regulated bus and readjust R68 if need be. One otherpoint, never substitute anything elsefor the F5 fusible link in the oven;not even fine copper, lead or wiresolder. F5 is a heat sensitive fuse,not an electrical fuse. It is the mainoven protection from burnout.

Eidson Electronic Co.Temple, Texas

December, 1971

rrv mrn[DJ®ITrn ©®~rrmw~WITH

"STACKABLEBUILDING

BLOCKS"Flexibility and system compatibility for TV remote controlare available with the Moseley Associates Stackable Building Blocks. Each individual Building Block is a completelyseparate and self-contained system. Building Blocks areavailable for remote control, automatic logging and status/alarm.

THE STACKABLE BUILDING BLOCKSPBR-30A/TV RemoteControl System ADP-220Automatic Data PrinterPBR-15A/TVRemoteControl System TAU-2Tolerance Alarm Unit

SCS-2Status SystemContact our Broadcast Marketing Department for full details onBuilding Blocks to fulfill your requirements.

MOSELEY ASSOCIATES, INC.SANTA BARBARA RESEARCH PARK

111 CASTILIAN DRIVE, GOLETA, CALIFORNIA 93017(805) 968-9621


59



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(Continued from page 59)distance, that meets all currenttransmission, pulsing and ringing requirements. One calculator, for theH-88 loading system, shows combinations of 22 and 24 gauge cables,and 24 and 26 gauge cables, forburied or aerial plant applicationswith central office limits of 1500,2200 and 3000 ohms. The othercalculator, for D-66 loop design,shows combinations of 22 and 24gauge cables for buried plant usewith 170~ 2000, 3000, 3500, 3800and 4300 ohm central office limits.In addition to providing completeinstructions for calculator use, thebulletin also describes design considerations of loaded and repeateredloaded loops, expected performanceof repeatered loops, one-man testsfor loaded loops, other loading systems, E-6 and other repeaters suitable for loop applications, andtabulated attenuation, resistance andmiscellaneous loss data.

101. ANIXTER-PRUZANTwo new catalogs prepared byAnixter-Pruzan show a full-line ofthe most up-to-date developmentsin both drop materials and grounding materials. Items in the 6-page

• TP-18Tape Cartridge

Winder

This rugged and dependable tape winder fills a need in everystation using cartridge equipment. Nolonger is it necessary to restrict yourcartridge operation to stock sizes, or totie up your conventional tape equipmentloading cartridges. The TP-18 handles allreel sizes (up to 3600' of 1 mil tape),winds new or old cartridges in any length.Available with or without Spotmaster tapetimer, providing precise minute and second calibration for creating exact-lengthtapes. TP-18 is $124.50, with Tape Timer$149.50. Lubricated tape and empty cartridges are also available.

BROADCAST ELECTRONICS, INC.----A Fllmw•Y•Company-----

8810 Brookville Rd., Silver Spring, Md. 20910

"Drop Material Catalog" include avariety of house drop cables, dropattachment hardware, house attachment hardware and passive devices. The four-page "GroundingMaterials" brochure lists groundrods and clamps, pipe groundingclamps and straps, ground wire,and ground wire moulding andstaples.102. COHU ELECTRONICS,

INC.-Two low light level TVcameras present a usable picturewith only 0.003 footcandles of illumination on the faceplate of thevidicon, and they can be aimeddirectly at the sun without damage.Details on these self-contained cameras are described in technical datasheet 6-579. One camera is enclosed for outdoor use, the indoorcamera has rear panel controls.

Amperex Electronic Corp. . . . . . . . . . . . . . 23Ampex Corporation -

Pro Video Div 28-37Andrew Corporation . . . . . . . . . . . . . . . . . . 43

Belar Electronic Laboratory Inc 13Broadcast Electronics, Inc 8, 58, 60

CBS Laboratories . . . . . . . . . . . . . . . Cover 2Canon Inc 5, Cover 3Cleveland Institute of Electronics 61Cohu Electronics, Inc. . . . . . . . . . . . . . . . . 1

Datavision 47Ditch Witch Trenchers Div. of

Charles Machine Works, Inc 17

Eimac- Division of Varian Assoc. . 45Electro Voice, Inc 19

Freeland Products Co 60

Gates Radio Company Div.Harris lntertype Corp. . . . . . . . . . . . . . . 9

Gotham Audio Corporation . . . . . . . . . . . . . 58The Grass Valley Group, Inc. . . . • . . . . . . . 3Gray Research . . . . . . . . . . . . . . . . . . . . . . 59

Clifford B. Hannay & Son, Inc 42

International Video Corporation 18-18A-18B

Jensen Tools and Alloys 60

Liberty Industries 47

McMartin Industries 10Minneapolis Magnetics, Inc 42Moseley Associates, Inc: . . . . . . . . . . . . . . 59

North American Philips 57Nortronics Company Inc 12

Potomac Instruments, Inc 55

RCACorp. CESDiv 46B, 46C

Sansui Electronics Corp. . . . . . . . . . . . . . . 7Shure Brothers, Inc Cover 4Spotmaster 8, 58, 60Stanton Magnetics, Incorporated 15

Taber Manufacturing & Eng. Co 10Tech Laboratories, Inc 58Telemation, Inc. . 39Telex Communications Div 51Television Computer 11

Wilkinson Electronics 46D




FM And Land Mobile

FCC ProposalsAmendment of Section 73.261(a) of the rules to

provide for licensing all FM Broadcast stations forunlimited time operation and to require them to maintain a minimum operating schedule of at least eighthours between 6 a.m. and 6 p.m., local time, and atleast four hours between 6 p.m. and midnight. localtime, each day of the week except Sunday, has beenproposed in a rulemaking notice by the FCC.

At present FM stations are required to provide aminimum of 36 hours per week during the hours 6 a.rn.to midnight, consisting of not less than five hours inany one day, except Sunday.

In proposing the change, the Commission pointedout that even though FM has become "economicallymore viable" a number of stations are operating at ornear the minimum level permitted under the rule. TheCommission said that when there are needs for moreaural service in many places, "this appears hardlyconsistent with the public interest." To the extent thatFM and unlimited AM are alike, the Commissionsaid, "it would appear that the same standard shouldapply in both instances."

In response to requests by the Associated PublicSafety Communications Officers, Inc. (APCO), andRY DAX, Ine.. for reconsideration of rules governingoperation of non-voice radio systems on voice channels in the land mobile services below 950 MHz(Docket 19086), the Commission has retained arequirement for identification of land mobile radiostations by voice, but has deleted a requirement forautomatic sensing of channel occupancy.

In an order adopted August 18, 1971, the Commission amended Parts 89, 91 and 93 of the rules to permitregular and expanded operation of non-voice operation in the land mobile services.

A PCO had asked for an exception to the requirement for station identification by voice to allow stationidentification by Morse Code and RY DAX had askedfor deletion of the requirement that non-voice systemsemploy automatic sensing or monitoring equipmentthat can prevent transmission on an occupied channel.The Commission said, in denying the APCO

request, that use of Morse Code would not affordsignificant advantages and noted that the additionaltransmitting time required could increase potentialinterference.

In granting the RYDAX request, the Commissionstated that it had originally required automatic sensingof channel occupancy to protect voice communications from interference by non-voice transmissionsand to assure that non-voice operations would ·besecondary to voice operations.

The FCC observed, however, that RY DAX, aswell as General Electric Company and RCA Corporation, had raised "significant questions" as to theeffectiveness and adaptability of automatic sensingdevices and said that while it would permit use ofthese devices, it would not impose a mandatoryrequirement for their utilization at this time.

December, 1971

"Want a Good Jobin Broadcasting?

¡.

l ''~\You'll Need a

First Class FCC License?'Matt Stuczynski knows. He's the Senior Transmitter Operator ofRadio Station WBOE. His story is typical of hundreds of men whohave used Cleveland Institute Training as a springboard to successin Broadcasting. Here's what Matt says about Cleveland Institute:"I giveCleveland Institute credit for my First Class FCC License.Even though I had only 6 weeks of high school algebra, CIE'sAUTO-PROGRAMMEDT" lessons really made electronicstheory and fundamentals easy. After completing the CIE course,I took and passed the First Class Exam. I now have a good jobin studio operation, transmitting, proof of performance, equipment servicing. Believe me, a Commercial FCC License is a'must' for a career in Broadcasting."

If you want rapid advancement in broadcasting, the first step is aFirst Class FCC ticket with your name on it. And Cleveland Institute Home Study is a fast, economical way to get one. What's more,CIE backs their licensingprograms with this money-back warranty:"A CIE License Course will quickly prepare you for a FirstClass FCC License. If you complete the course but fail to passthe exam 011 your first attempt, CIE will refund all tuition."

With Cleveland Institute you get your First Class FCC License oryour money back! Send coupon today for FREE book or write toCleveland Institute of Electronics, 1776 E. 17th St., Dept. BE-73Cleveland, Ohio 44114.

ENROLL UNDER NEW G.I. BILLAll CIE courses are available under the new G.I. Bill.If you served on active duty since January 31. 1955, orare in service now, check box in coupon for G.I. Billinformation.

' MAIL COUPON TODAY FOR FREE BOOK@eIE Cleveland Institute

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61



PROFESSIONAL ~~OOWíl~~~

VIR JAMESCONSULTING RADIO ENGINEERSApplications and Field Engineering

345 Colorado Blvd.Phone: (Area Code 3031 333-5562

DENVER, COLORADO 80206Member AFCCE

TWX 910-931-0514

WALTER F. KEANCONSULTING RADIO ENGINEERS

P.O. Box 4201Santa Fe. New Mexico 87501

Phone: 505-983·5175

Member AFCCE

CAMBRIDGE CRYSTALSPRECISION FREQUENCYMEASURING SERVICE

SPECIALISTS FOR AM-FM-TV445 Concord Ave. Phone 876-2810

Cambridge, Mass. 02138

COURTRIGHTENGINEERING

MORRIS COURTRIGHT, Jr., P.E.Automation . Applications Field Engineering

ELECTRICAL AND BROADCASTINGRoute No. l. Box 854A, Flagstaff. Ariz. 86001

Phone (602) 774-8206

RALPH E. EVANS ASSOCIATESConsulting Radio EngineersAM • FM. TV - CATV - ITFS3500 North Sherman Blvd.

MILWAUKEE, WISCONSIN 53216Phone: 414-442-4210

TODD ASSOCIATES

CONSULTING RADIO ENGINEERSAlva C. Todd, Ph.D., P.E., Principal

827 S. Summit Avenue, Ph: (312) 832-4104VILLA PARK, ILLINOIS 60181

SESCO, Inc.47 NICHOLS AVENUE

P. O. BOX 518

(206) 378-2137

FRIDAY HARBOR,WASHINGTON, 98250

Equipment for Sale"New & Used Towers, Buy, Sell or Trade.Erect. Ground wire 85¢ lb. Bill Angle.919-752-3040, Box 55, Greenville, N.C.27834." 2-71-tf

62

Equipment for Sale (Cont.)HELIAX-STYROFLEX. Large stocks -bargain price - tested and certified.Write/call for price and stock list. Sierra-Western Electric. Box 23872, Oakland,Calif. 94623. Tele: (415) 832-3527. 1-71-tfONE STOP for all your professional audiorequirements. Bottom line oriented.F. T. C. Brewer Company, P. O. Box8057, Pensacola, Florida 32505. 7-71-tfCARTRIDGE TAPE EQUIPMENT-Co~pletely rebuilt and reconditioned. Tapecaster and Spotmaster Record/Playbacks$375.00. Playbacks $250. 30-day moneyback guarantee. AUTODYNE, P. O. Box1004, Rockville, Maryland 20850 (301/762-7626). 11-71-tfUSED EQUIPMENT-Pay Cash for FM/AM transmitters, antennas. consoles. etc.Contact: Electrónica Fernández, Box 415,Hato Rey, Puerto Rico 00919, Tel.: 767-3500. 11-71-4tSale-50% off on all factory new RSCoils, Contact ors, Chokes, Switches,Sampling Transformers. Loops, etc. Stockitems. Quick delivery, Geleco Electronics, Ltd., 2 Thorncliffe Park Drive, Unit28. Toronto 17, Ontario. Phone (416) 421-5631. ll-71-2tCIRCA 1947Western Electric 506-B-2 tenkilowatt transmitter plus spare parts inventory; just retired from daily use. Bestoffer over $500. Can be bought completewith RCA BTE-10-B stereo exciter (notavailable separately) at best offer over$1,1250. (Blind box reply). Dept. 257Broadcast Engineering, 1014 Wyandotte,K. C., Mo. 64105. 12-71-ltThe University of California offers forsale to the highest bidder 2 only AmpexVR 1100 Videotape Recorders. With MarkTen heads, one playback only. Accessories: Electronic Editor. Vertical LOCBoards, Processing Amplifier, MincomDropout Compensator. Smith Tape Splicer.Minimum acceptable bid for lot $20,000.Sealed bids must be submitted to University of California, Purchasing Department.Santa Barbara, Calif. 93106 no later than2:30 P.M., December 17, 1971. For bidforms. please contact above address orcall A/C 805 961-2588. 12-71-ltFOR SALE: Two Dage B/W solid stateModel 520 cameras with cable and CCU's.Two Quickset Gibraltar tripods withcradle head and Hercules dolly. OneDage/Miratel Dual 8" rack mount monitor (tube). One Dage 585 solid state digitalsync generator with Genlock (RS-170Spec.), All in like new condition. Willsell in part or make package. Best offer.R. Stern, 15W631Patricia Lane, Elmhurst,Ill. 60126. Tel. 312-279-8482. 12-71-ltVSI-2200 Film Multiplexer and Spindler& Sauppe Model 332 Slide Projector withLens and Base for Sale. $2.250.00. SMU,TVSystem. (214)363-5611ext. 811.12-71-ltKTR-1000 COLOR TV MICROWAVELINKS-NTSC Color TV plus programaudio microwave links for studio-xmtr,CATV,etc. Rack mounted. Mfr. Raytheon.25 sets in stock, as new condition. RadioResearch Instrument Co.. Inc., 3 QuincyStreet, Norwalk, Conn. Tel. 203-853-2600.

12-71-4tFOR SALE: l. AMPEX VR-660 VideoTape Recorder. 2. 3M Monochrome Dropout Compensator. 3. AMPEX -05 IntersyncUnits 4. AMPEX Mark-111 Video Head.All excellent condition. KOREX. P.O. Box65725.Los Angeles. Calif. 90065 12-71-ltFOR SALE- 2 IVC 800 Series l" ColorVTR's. Excellent condition-Priced to sell-Call (402) 477-0533or write T-V Transmission Inc., P.O. Box #81304. Lincoln,Nebr. 68510. 12-71-2t"AMPEX" 354, lowtime heads. bridgingtransformers, factory console. first $1100takes. Box 44, New Bloomfield. Mo. 65063.

12-71-lt

ServicesREGISTEREDElectrical Engineer specializing in broacast automation and monitoring field will work with your engineer onplanning, maintenance. and design problems. Have facilities for custom equipment manufacture. Carroll W. Swain,27272 12th Place South, Kent. Wash.98031. Phone 206-839-5556. 12-71-ltCRYSTAL & MONITOR SERVICE, Frequency change, repair or replacement ofoven type broadcast crystals. Also frequency change and recalibration or repairof AM frequency monitors. and H-P FMmonitors. Fast service at reasonableprices. 30 years experience! Call or write:Eidson Electronic Co. Box 96, Temple,Tx. 76501. Pho. 817 773-3901. 9-70-tf

Services (Cont.)ADVISORY & INSPECTION SERVICEfor the CONSTRUCTION & MAINTENANCE of TALL TOWERS. Dept. 257,1014 Wyandotte St., Kansas City, Mo.64105. ll-71-2t

Help WantedField Service and Transmitter Testing:CCA Electronics has immediate openings for experienced AM and FM transmitter engineers, preferably Chief Engineers. who are familiar with the technical phase of a broadcast station operation. CCA is expanding its total serviceto the broadcast industry and requirescompetent technical people in our service growth. Supply resumes togetherwith salary requirements to: BernardWise. President, CCA Electronics. 716Jersey Avenue, Gloucester City, N.J.08030. 11-71-2tJob Headquarters for all Radio and Television Engineers. Immediate openings exist in 9 western states and elsewhere forqualified engineer and technical personnel. All categories from trainees to experienced transmitter maintenance. chief.assistant chief. live color video maintenance and technical operations. Send usyour complete resume now. The AMPSAgency, 11661 San Vicente Blvd., Suite300, Los Angeles. Calif. 90049.Telephone:213-820-2678. By Broadcasters - ForBroadcasters. 11-68-tfMICROWAVE ENGINEER. Microwavemaintenance engineer wanted to maintain450 miles of Lenkurt 76 TV in Nevada.Must be familiar with video basebandequipment, and audio sub-carriers. Company car and benefits. Salary open. Sendresume to Personnel Department. DonreyMedia Group, P.O. Box 1359, Fort Smith,Arkansas 72901. 12-71-2t

TrainingTo advance in electronics. knowledge andability are required. Grantham offerscorrespondence and resident instruction.in depth, leading to the degree of Associate in Science in Electronics Engineering. G. I. Bill approved. Credit for previous training and experience allowed.Free Catalog. Write: Dept. E-2. GranthamSchool of Electronics. 1505 N. WesternAve.. Hollywood. California 90027. 6-67-tfFirst phone through tape recorded lessonsat home plus one week personal instruction in Washington, DC. Atlanta. Boston.Detroit. New Orleans. Minneapolis. Seattle, Denver. Portia n d , Los Angeles.Proven results. Our 17th year teachingFCC license courses. Bob Johnson RadioLicense Preparation. 1060DDuncan, Manhattan Beach. Calif. 80:l66. Phone 213-379-4461 1-69-tfIMMEDIATEOPENINGS: Qualify for anyof the following positions: RCA CCTVEquipment, monochrome or color. Salesmen - TV Systems Engineers - ProjectEngineers - Supervisors - Managers -Maintenance Technicians - Video Engineers - to work either New York. Pennsylvania. New Jersey or California area.Write: RCA Rep., P. O Box 268, NewHyde Park. New York 11040. 4-70-tf

Radio Station For Sale5,000 WATT AM RADIO DAYTIMER.$150,000-29% down-$45,000 real estateoptional. Box 880. Willcox, Arizona.

7-71-5tTV STATION FOR SALE-Complete television station available for package priceof $12,000. f.o.b. KETC-TV transmitterroom at Boatmen's Bank Building, St.Louis, Mo. Equipment in package includes: 320-foot Bio-Knox self-supportingtower. 320 feet of 3% inch transmissionline, RCA TT5 transmitter driver with GE20 kw TF-4 amplifier. two Ampex VR-1000 videotape machines (one completewith Allen mod. demod & switcher) withAmtec. one Eastman 275 film projector,one GE 4-TV-86-C-l multiplexer, oneSpindler 35mm slide projector. and oneGE 4-PC-13-A-l vidicon film camera withGE 4-TC-58-A-l controls. This equipmentis now in daily use but will be retiredfrom service with opening of new KETCTV Broadcast Center November l. Thisis first and last time this equipment isbeing offered and it won't last long atthis package price. Station prefers to sellas a package, but would accept offers onindividual items. For more ínforrnatíonwrite: Director of Engineering, KETC-TV.6996Millbrook Blvd., St. Louis, Mo. 63130(or phone 863-0998). 12-71-lt




Shoppíne for lenses?Compare Canon!

Draw up a checklist that includesprice, specifications and image brilliance, then start comparing catalogues. You'll probably come up withthe Canon answer, like so many majorcamera producers-for broadcast 1"or 1 1/4" PLUMBICON® or CCTV 1",2/3" vidicon.

Stack these two Canon popularityfavorites against anything else on themarket and see what we mean.The Canon TV Zoom LensP17X30B2 has an impressive1:2.5 relative aperture atfocal length range (440-500mm), in spite of its17X zoom ratio. At 30-440mm it's a remarkable1:2.2, offering the same performance as our P10X20B,specially designed for maximum versatility with three different rangeextenders.

Both are ideal for a variety of situation, including dim lighting and openareas like field events.

Here are some other examples ofthe wide Canon line:

ManualName Range of Focal Length Zoom Ratio Maximum Relative Aperture

n~"PLUM81coN ¡P11 x 3082 30-500mm 1 : 17 F 2.2PlO X 20 20-200mm 1 10 F 2.2

l" PLUM81CON IPV17x248 24-40Cmm 1: 17 F 1.8PVlO X 16 16-160mm 1: 10 F 1.6PVlO x 158 15-150rnm 1: 10 F 2.0

l" Vidicon IV10xl5 15-150rnm 1: 10 F 2.8V6 x 16 16.9- 9Smm 1 : 6 F 2.0V5 x 20 20-lOOmm 1: 5 F 2.5V4 X 25 25-lOOmm 1: 4 F 1.8

%" Vidicon IJ!Oxl3 13-130·11m 1: 10 F 2.8J 6 X 13 13- 76mm 1: 6 F 1.9J 5 X 15 15- 75mm 1: 5 F 2.1J 4 X 12 12.5- 50mm 1: 4 F 1.8

Servorized/MotorizedName Rangeof Focal Length Zoom Ratio Maximum Relative Aperture

1Yi"PLUM81CON I Pl OX 2084 20-200mm 1: 10 F 2.2l" Vidicon I VlO X 15R (OCJ 15-150mm 1: 10 F 2.8

V6 X 16R (AC/DC) 16.9-95mm 1 : 6 F 2.0IV4 X 25R(AC/DC,EE) 25-lOOrnm 1 : 4 F 2.5

® N.V Philips of Holland

• CANONU.S.A., INC.: 10 Nevada Orive, Lake Success, Long Island, New York 11040.U.S.A. (Phone) 516-488-6700• CANONU.S.A., INC.: 457 Fullerton Ave.. Elmhurst. Illinois 60126, U.S.A. (Phone) 312-833-3070 • CANON OPTJCS& BUSINESSMACHINES CO., INC.: 3113 Wilshire Blvd .. Los Angeles. California 90005, U.S.A. • CANON AMSTERDAMN.V.: Gebouw 70,Schiphol Oos t. Holland • CANON LATIN AMERICA, INC.: Apartado 7022, Panama 5, Panama • CANON !NC.: 9-9, GinzaIi-cnorne. Cbuo-ku. Tokyo 104, Japan Canon




A production conrole*for $312 !

Eureka! A complete remote and studio production console for a fractionof what you'd expect to pay for a console with comparable features andperfonnance! Simply purchase a new Shure M675 Broadcast Master andthe extremely popular Shure M67Professional MiicrophoneMixer. By combining these two units*, you get inputs to handle microphones, turntables,phone lines and tape machines- with cuing provision on line and magnetic phono inputs. Result? A versatile low-noise, low-distortion broadcastproduction console for in-studio, remote, and standby assignments; acomplete CATV console; a studio production console. All for $312! Forcomplete technical data, write:

ShureBrothers Inc., p222HartreyAve.,Evanston,Ill. 60204. ~*Each model is also available separately: M67 - $162 net; M675- $150 net.

Circle Numb~r 3 on Reader Reply Card



Broadcast Engineering. - americanradiohistory.com · 2019-07-17 · DECEMBER, 1971175 cents...

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Transcript of Broadcast Engineering. - americanradiohistory.com · 2019-07-17 · DECEMBER, 1971175 cents...