July 1977Copy nr.: 8 ■

OPERATING MANUAL

FOR

DIRECTION FINDING ANTENNA(PROTOTYPE)

LIST OF CONTENTS

P a r a g r a p h P a g e

1 . 0 . G E N E R A L I N F O R M A T I O N 1 - 2

1 . 1 . I n t r o d u c t i o n 1 - 21 . 2 . E q u i p m e n t l i s t * 1 - 21 . 3 . O p e r a t i n g p r i n c i p l e s 1 - 31 . 4 . G o n i o m e t e r c i r c u i t d e s c r i p t i o n 1 - 1 |1 . 5 . P r o v i s i o n a l s p e c i fi c a t i o n s 1 - J +

2 . 0 . A S S E M B L Y A N D S E T T I N G - U P 2 - 12 . 1 . G e n e r a l r e m a r k s 2 - 12 . 2 . M e c h a n i c a l a s s e m b l y o f a n t e n n a 2 - 3

3 . 0 . O P E R A T I N G I N S T R U C T I O N S 3 - 13 . 1 . S e t t i n g u p 3 - 13 . 2 . F a m i l i a r i z a t i o n p r o c e d u r e 3 - 13 . 3 . O p e r a t i o n a l p r o c e d u r e s 3 - 33 . ^ . U t i l i z a t i o n o f a n a u t o m a t i c d i r e c t i o n fi n d i n g r e c e i v e r 3 - h

LIST OF ILLUSTRATIONS

F igu re

1 - 1 O u t d o o r a n t e n n a s e c t i o n v i e w 1 - 11 - 2 G o n i o m e t e r u n i t c i r c u i t d i a g r a m 1 - 52 - 1 O p e r a t i o n a l s e t - u p 2 - 2

FIGURE 1 - 1

OUTDOOR ANTENNA SECTION VIEW

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1.0. GENERAL INFORMATION

1.1 . In t roduct ion

The prototype direction finding antenna system is designed tooperate in the 45 to 50 MHz frequency range.It consists of the actual fixed antenna section to be set upoutdoors, and a remote goniometer control unit.The goniometer output will go to any suitable signal strengthmonitor receiver such as a HRR-18. The monitor receiver determinesthe direction of signal arrival in combination with the goniometerBEARING control knob position.As an alternative the outdoor antenna section may be used on its ownto feed into an automatic direction finding receiver such as theHRR-26.The antenna configuration, a pair of crossed horizontal dipoles witha vertical whip at their center, was chosen to simulate the generalappearance of regular apartment building common antenna systems.A provisional photograph of the outdoor antenna section is shown infigure 1 -1 .

1.2. Equipment list

The prototype antenna system delivery consists of the followingitems:

1 goniometer control unit3 antenna pre-amplifiers SRA-3S3 power supplies UWP-663 coaxial cables 40 cm in length1 coaxial cable 80 cm in length3 coaxial cables 15 m in length1 antenna mast section 140 cm in length, 5 cm diam.1 antenna center assembly with 3 fixed coaxial cables.4 half horizontal dipoles with each 2 glands and 2 swivels1 vert ical antenna rod1 antenna cover cylinder1 cover top lid with gland and swivel1 cover bottom l id4 red-marked stainless steel machine screws and spring washers M31 blue-marked di t to

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1 set of spare machine screws and spring washers M31 socket wrench 13 mm1 hex wrench 5 mm1 wooden gland positioning tool6 manuals

1.3. Operating principles

The outdoor antenna section comprises two horizontal dipoleantennas which are oriented at right angles, i.e. one is in aNorth-South direction and the other is in an East-West direction.Each dipole output is passed through a low-noise pre-amplifierand an extension cable to one of the stator coils in the goniometerunit. Within each stator coil a magnetic field wil l be producedwhich is related directly to the amplitude and phase of the signalintercepted by the corresponding dipole.Two dipole antennas feed two independent stator coils which areassembled at right angles. The combination provides a magnetic r.f.field distr ibut ion wi th in the stator coi l area which is a c lose repl icaof the r. f . fie ld that prevai ls at the antenna s i te .If within the stator coi l area a small pick-up rotor loop is rotated,i ts r. f . output wi l l resemble that of an actual loop antenna rotat ingat the outdoor antenna site.The rotor loop output wil l show a figure-of-8 directional patternin dependence on the rotor orientation and the direction of arrivalof an incoming signal.By monitoring the maxima and/or minima in the rotor loop output onecan find the direction from which the intercepted signal came, exceptthat there is a 180° ambiguity, i.e. "front" and "back" maxima arethe same.In order to solve this ambiguity a third so-called SENSE antenna hasbeen added. It consists of a vertical quarterwave whip at the centerof the previous horizontal antenna cross.It exhibits an omnidirectional pick-up pattern and provides a phasereference for the previous goniometer rotor output signal.When added to the previous rotor output, it will enhance one lobe andoppose the other lobe, such that a clear distinction between "forward"and "backward" can be obtained. For a given amplitude of this addedsignal the rotor direct ive pattern wi l l be modified into a cardoidwith one maximum in the "front" and one null in the "back" direction.

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1.4. Goniometer circuit descript ion (see fig. 1-2)

The center of figure 1-2 shows the actual goniometer element.It has two crossed stator coils.Each stator coil is matched by external components to providea proper termination for the N-S or E-W antenna outputs.Within the stator coil area there is a rotor assembly controlledby a frontpanel control knob designated "BEARING".The rotor assembly comprises two crossed pick-up coils. The outputsignal from one of these coils is used, via its own matching meansand a 6-6-6 dB signal combiner, to feed the signal strength monitorrece iver.The second rotor coil output is not used bu is terminated in amatched dummy load. Its purpose is to preserve a constant terminationfor the two stator coi ls irrespective of the rotor assembly orientat ion.

The "SENSE" antenna output signal must be added to the goniometerrotor output to resolve the 180 bearing ambiguity.The sense signal is introduced via the previously mentioned 6-6-6 dBsignal combiner.The added signal must be of the proper phase and amplitude to obtainthe desired amount of bearing preference. The SENSE path thereforecomprises a frontpanel-controlled step attenuator and a frontpanel-con t ro l led de lay - l i ne .The delay line is built up from binary related lengths of coaxialcable which can be switched in or out of the circuit by means offrontpanel switches.The sense signal addition can thus be set up as close as 1 dB inoamplitude and 5,5 in phase related to the desired value.For quick comparison during the adjustment the SENSE signal can beswitched on and off by a toggle switch on the frontpanel.

1 .5- Prov is iona l spec ificat ions

Frequency rangeAntenna polarization

Equivalent noise figureDirection finding azimuth coverageBearing accuracy

R.f. impedanceGoniometer unit antenna input VSWRGoniometer unit bearing channelsinser t ion loss

45 - 50 MHzhor i zon ta l f o r bea r i ng , ve r t i ca lfor sensebetter than 5 dB at antenna terminals360°consistent with determination ofmaximum in directive angular response+/- 7,5°nominally 50 ohmsless than 1.5

maximally 13 dB on main lobes

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Goniometer unit maxima/null ratioGoniometer unit maxima error

Pre-ampl ifier ga inPre-amplifier input VSWRMaximum coaxial extension cable lengthSupply power

Operating temperature range

maximally 8dB with attenuatorat zeroat least 21 dBless than 0.7 dB over 360°bearing range27J +/- 0.4 dBless than 1.360 m of RG-58consistent with three SRA-3/UWP-66 combinations.antenna section -20 C to +60 Cgoniometer unit -10 C to +50 Cpre-ampl ifiers consis tent wi thSRA-3 specificat ions.

Outdoor antenna dimensions

Goniometer unit dimensions

approx. 290 x 290 x 165 cm-o v e r a l l

3approx. 10 x 12 x 20 cm .

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2.0. ASSEMBLY AND SETTING UP

2.1. General remarks (see figure 2-1)

The general layout and set-up of the direction-finding antennasystem is as follows:

a. The actual antenna section must be sited outdoors, i.e. on aroof top.It is recommended to use such a mast extension length that thecentral antenna section is at least 2.5 m above the roof topsurface.The area around the actual antenna should be as free as possiblefrom intervening or reflect ing objects or structures.A clearing of at least 10 m from such objects is strongly recommended.In order to normalize bearing determinations it is advised to orientthe antenna system such that the folded dipole half marked with al i t t le whi te tape flag po in ts t rue Nor th .If necessary, use guy wires to improve mast rigidity.

b. Three coaxial cables, 3-5 m in length, emerge through the lowerlid of the central antenna box.These cables should plug onto the inputs of three SRA-3 low-noisepre-amplifiers. The three 15 m coaxial extension cables should thenbe plugged onto the three SRA-3 amplifier outputs.The extension cables are led or passed through to the goniometerand receiver control posit ion.All these elements are color-marked, keep green to green, red to redand blue to blue.For temporary environmental protection the plug-to-receptacle junctionin the open air should be sealed with tape, silicone rubber orplastic bags. A more permanent protection could be provided with somekind of closed box with the cables emerging through the bottom.If necessary, the extension cables of 15 m length may be extendedfurther by additional RG-58 cables provided that the total cable rund o e s n o t e x c e e d 6 0 m i n l e n g t h . • ■Cut these extra cables exactly (within e.g. a few em's) to the samelength .Seal the plugged connections.Color-mark these new cables carefully using the same standards as theexisting components.

c. The three cable ends, when they have entered the control and monitorposition, are plugged onto the "PRE-AMP" inputs of the UWP-66 powersupplies. The "RCVR" output receptacles on the UWP are connected tothe three antenna input receptacles of the goniometer unit, usingthe three 40 cm coaxial cables supplied.Be sure that the color-marks on extension cables, on UWP-66, on 40 cmcables and on goniometer are really matched.

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d. Use the 80 cm coaxial cable as supplied to interconnect thegoniometer unit output receptacle marked RCVR to the receiverr . f . i n p u t .Connect the UWP-66 power cords to an appropriate a.c. outlet.

e. When the antenna system, without the goniometer unit, is usedin conjunction with an automatic direction finding receiver, suchas the HRR-66, the output ends of the three ko cm interconnectioncables should be run from the three UWP-66 outputs to the threeHRR-66 inputs.Notice the appropriate functions as follows:

- The blue-marked cable is the SENSE antenna output.- The green-marked cable is connected to the horizontal dipole

(marked with a white tape flag) which runs North-South and thushas maximum signal pick-up from directions East and West

- The red-marked cable connects to the dipole which runs East-Westand thus has maximum signal pick-up from directions North and South.

2.2. Mechanical assembly of antenna

The outdoor antenna is shipped in parts which have to be reassembledon the spot. The following instructions for assembly should be followedin the order given.

a. Locate the nylon-and-aluminum central antenna assembly block.Locate the long single-rod vertical whip.Locate a blue-painted pointed 3 mm machine screw from the bag of screws.Insert the whip end which has a small hole in the side into thenylon coaxial hole of the central section. Take care not to damagethe brown transformer wires through which it has to pass.Orient the whip such that the previously mentioned small hole in theside is lined up with the blue-marked hole in the nylon member.Then insert the blue-marked 3 mm machine screw with its spring washerinto the blue-marked hole and use a screwdriver to fasten thescrew into the bottom end of the whip side wall.

b. Locate the 4 folded halves marked green and red. Check that each tubeend carries its swivel and its gland, the gland being approximately5 cm from the end.Locate the red-painted pointed machine screws from the bag of screwssuppl iedUse the 13 mm pipe wrench to loosen the stainless steel screws on thebottom end of the central assembly aluminum member a few turns such thatsome space prevails between the two round aluminum halves.Locate the big plastic cover, without l ids, and posit ion it around thecentral assembly block. Mind the inside marking "TOP".Carefully noticing and minding the color markings on folded dipole halvesand on the central assembly block,insert the dipole halves through theholes in the plastic cover and then in the aluminum and nylon holes ofthe central assembly block.

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Insert and fasten the red-painted 3 mm pointed machine screwswith their spring washers in the red-marked holes of lugs andnylon block.Thereafter, use the 13 mm pipe wrench to fasten the red-markedstainless steel screws at the bottom of the aluminum centralassembly block. Tighten them in steps working around.

• Use the wooden rod supplied to move the glands on the foldeddipole halves such that they nest in the holes and recessesof the big plastic cover.Then fasten the corresponding swivels in a few passes around.Do not use tools, manual force is adequate. It will be foundthat the plastic cover and the central assembly will be self-center ing dur ing the fixat ion.

, Locate the plastic cover bottom lid and pass the three coaxialcables through its 6 em center hole.Then screw the bottom lid with manual force only to the bottomof the big plastic cover.

Locate the plastic cover top lid, move it over the vertical whipand screw it onto the big plastic cover with manual force only.Then locate the last swivel and gland, move the gland over thewhip unti l l i t nests properly in the recess on the plastic top l id.Use the swivel to fix and seal the whip to the top lid.

Locate the 143 cm long mast section and insert the 5 cm diameteraluminum bottom end of the central assembly block into the mastsection that carries two M5 pointed screws.Then fix these machine screws with the supplied 5 mm hex wrench.This completes the reassembly of the outdoor antenna system.In case of need a set of spare machine screws will be found withthe de l i ve ry.

Fasten the supplied 143 cm long mast section to the customer'sstructure which will bring the antenna central assembly up to thedesired heigth above the roof top surface.Upon delivery one of the folded dipole halves carries a litt lewhite tape flag. It is recommended to orient the antenna structure suchthat this dipole end points in a true North direction in order tolet the goniometer bearing scale read true geographically relatedbear ings.

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3.0. OPERATING INSTRUCTIONS

3.1• Setting up

The setting-up procedure and the assembly of the demountableantenna have been described in section 2 of this manual and thegeneral layout is depicted in figure 2-1.The following procedures assume that these steps have been completedand that actual direction-finding on target signals is now imminent.

3.2. Famil iarization procedure

In order to get acquainted with the equipment, with alternativeoperat ing modes, with possibi l i t ies and with l imitat ions i t isrecommended to do some test runs on a controlled signal.For this one may set up the target transmitter to be used at a fixedspot e.g. several hundred meters away and preferably on an unobstructedpath between transmitting and receiving locations.Activate the transmitter, the receiver and the goniometer pre-amplifierpower supplies. Tune the receiver to the transmitted signal and thenproceed as follows:

a. Move the goniometer front-panel switch marked SENSE into its OFFposition. This leaves only the horizontal antenna dipoles in operation.Now rotate the goniometer BEARING control over 360° and observe thattwo maxima and two minima in received signal strength are found.This represents the figure-of-8 direct ional pattern of the hor izontalantenna means.If necessary, adjust the receiver gain such that the receiver isoperating linearly and at no more gain than necessary to make theobservation.

b. Read the BEARING angles for which the maxima and minima in signalstrength occur.It will be found that one maximum corresponds to the actual directionof the target transmitter and that the other equally strong maximumis displaced by 180° in bearing.Also, the two minima in signal strength will be found to differ by90 in bearing from the direction of maxima.It will be clear that such a bearing determination leaves a 180°ambiguity in the true target direction. This can under circumstancesbe acceptable if some foreknowledge about the possible whereabouts ofthe target is avai lable.

c. One observation that can be made is that the minima in signal strengthcan be determined more accurately than the direction of maxima.The direction of maxima, due to a fairly broad nose of the antennalobe, is mostly derived from a mental averaging between bearings wherethe signal strength falls off perceptibly on both sides of the maximum.

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Usually, in the interest of accuracy, one would determine transmitterbearing from the minima, taking into account their 90° angulardisplacement with respect to the true bearing.If however the intercepted signal is very weak, one will have toaim for the maxima and accept the decreased accuracy.

d. In order to solve the 180° ambiguity mentioned above, the SENSEcapability has been added.This feature al lows the or ig inal figure-of-8 pattern to be distortedinto a cardoid directive pattern that has only one maximum andonly one minimum.During the present trial run this capability can be set up asfo l l ows .Adjust the BEARING control knob to the signal maximum which is known tobe the false one (back instead of front).Now move the goniometer switch marked SENSE over to its ON position.Manipulate the SENSE AMPLITUDE attenuator switch and the SENSE PHASEswitches such that the monitored signal strength becomes as low aspossible. It will be necessary to go back and forth between these twocontrols a few times in order to attain maximum signal suppression.During this procedure the BEARING control knob should be left alone.If this condition of maximum suppression of the back lobe has beenachieved one can check and see that 360 rotation of the BEARING controlwill produce the desired cardoid pattern, providing one signal strengthmaximum in the correct target direction and one minimum in the opposited i rec t i on .One may also notice that the determination of bearing of the signalmaximum is slightly more difficult due to the fact that a cardoidhas a broader lobe nose than the previous figure-of-8 pattern.Determination of bearing from the signal minimum may not be sodesirable because, due to imperfect suppression adjustment, the singlenull may on closer inspection consist of two neighbouring nulls(imperfect amplitude balance) and/or the two nulls may be unequal andbe displaced sl ight ly f rom the theoret ical d irect ion ( imperfect phasebalance).

e. There may be two ways to avoid the 180° ambiguity and to retain thebetter accuracy of the sharper figure-of-8 lobe nose.With the SENSE adjustment set up as in the previous step d. , onedetermines the general target direction by means of the cardoid patternwhen the SENSE switch is in the ON position.The SENSE switch is moved to its OFF position and one concentrates only .on the maximum lobe thus indicated and tries to find the best bearingapproximation from the figure-of-8 lobe.

f. Another way to avoid the ambiguity and retain best lobe nose sharpnessis as fol lows.With the SENSE adjustment set up as described in the previous stepd, one simply increases the SENSE AMPLITUDE attenuator setting by some6 to 12 dB. Thereby the bearing angular pattern will become somethingbetween a figure-of-8 and a cardoid.

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In that case the actual target direction is indicated by thestrongest of the two maxima that are found when the BEARINGknob is rotated over 360 , thus providing an unabiguous result.Furthermore, the lobe nose has a sharpness which is nearly equalto that o f the or ig ina l figure-o f -8 pat tern .

It is believed that the operator, having gone through these procedures.will have acquired a feeling for the ways to obtain the best resultsfrom the available means.Because of its importance it may be repeated that during the wholeprocedure the monitoring receiver should operate in its l inear region.No a.g.c, i f avai lable, should be used.It is also a fact that, when judging signal strength aural ly,the best discrimination will be obtained with the lowest acceptablesound volume..

3.3. Operational procedures

The previous familiarization procedure represented an ideal situationover a wel l-control led r. f . path and a stat ionary target.Actual operational conditions may be less favourable.It may serve to describe some of the effects that produce the differencesuch that they may be recognized and be taken into account by the operator.

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a. The actual r.f. path between transmitter and receiver may not be adirect one, but may be along various reflections from buildings,s t ruc tu res , e t c .These indirect paths may vary rapidly for moderate changes in targetp o s i t i o n .The operator will then find that the signal strength varies andflutters and that the precise angle of arrival moves around some mean.He can counteract this to a certain extent by rapidly moving theBEARING control knob back and forth around such a mean and mentallyaveraging to the most likely mean position.

b. The setting-up of a true cardoid pattern adjustment depends criticallyon the field st rength rat io of hor izonta l ly and ver t ica l ly polar izedincomint signals. The target antenna characteristics are somewhatarbi t rary and thus both ver t ica l ly and hor izontal ly polar ized fieldcomponents will exist at all times. The ratio between them willhowever be affected by the target aspect and by eventual inhomogenitieson the path.One should therefore not expect that the cardoid pattern will beretained under all conditions. The best that under actual conditionscan be expected is a clear distinction of the stronger front lobewhich takes away the 180 ambiguity.At a low incidence rate and under adverse conditions one may find thatthe front and back lobe occasionally change position.This is in the given set-up unavoidable and only a regular and prolongedobservation period will help to avoid wrong conclusions from thisanomaly. It is such that a single bearing observation should not bet r u s t e d b l i n d l y.

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c. The presence of reflecting structures near the outdoordirect ionfinding antenna wi l l affect the ul t imate bear ingaccuracy adversely. As an example it may be mentioned that alaboratory test set-up in which the antenna was located approximately8 m. in front of a building and well below roof level gave riseto bearing errors of up to 8 or 10° with a rotational periodicityof 45 between successive maxima or minima in deviation.

3.4. Ut i l izat ion of an automat ic d i rect ionfinding receiver

The antenna system without the goniometer unit can be used inconjunction with an automatic direction finding receiver with scopepresentat ion.The proper connection mode is described in sec. 2.1. and depicted infigure 2 -1 .The automatic receiver is at an advantage not only for its instantaneousindication which under adverse propagation conditions helps to sortout the mean bearing from fluttering indications, but also because it onlyreacts to SENSE signal phase and ignores SENSE signal amplitude.For operation of such an automatic direction finding receiver,such as the HRR-66, reference is made to the corresponding manual.

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