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A PUBLICATION FOR THE RADIO AMATEURESPECIALLY COVERING VHF, UHF AND MICROWAVES

VOLUME No.9 AUTUMN 3/1977 DM 4.50

ULM 70

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VHFCOMMUNICATIONSPubll ,I lH by:Verlag UKWSEAICHTE Hlnl J . Oohlul aHO . Jlhn,lran. 1 0-8523 BAIERSOORF .Fed . RIp. 01 Gem1any . Tal,phon.. CO 91 33)!5!l, 850 ,Pub" ' ''',r,:T. Billln, H Dohlul .Editor, :Ter ry O. BIII.n, G 3;Va I OJ0 so . rnpoollblilor Ihl textRobe rt E. Lentz, OL3 WR. rnponllbl,lor Ii'll lechnlc.ll cont."tIAdu r t l, lng mlnag . r:T. BIUl n.VHF COMMUNICATIONS,tr.. lnt. rnatlonal lIditlon of Ih l Olm'llln publication UKWBERICHTE, II qu.r1lrty Im ltaurrad io mlgazl". npecl"ly c l t 'rlog lor th l VHFIUHF/SHF technology. II I, pub liah.cl InSp ring, Suml'Mr, Autumn , and Wintar , Thl lublcrlplion price 'I OM 11'.00 or "allonal equivalent per y r, Indiyldual copl,r. . . . . . i l.bl . It OM .50. or equivalen t, Neh . Sublcrlpll on"ord 01 lnd....ldu.l copla. pureh._ 01 P.C.boIiraa and ad vl r t iMd apecill componlnll.ad rtiNm,nta and contrIbution, to the m . g U I ~ .nould be addrHHd 10 thl nilioo-I rep . . .""talive .e Verteg UKW.BERICHTE 18nAll rlghl. r... ~ AltPrintl . tranilitioni or IdrlCU only Wth thl wrillin approvll 01 lhepublllhif.Printed In the FIIC! , Alp . 01Glrmlny by A, Allchenblch KG . Krellngllr.39 . 8500 Nutlrnblrg

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...... J. 00II c..o_lIoIt a .n - -n WIl!!j.tlo,11010,l1li; ~ K . , W I I E ' " 11 .1.._l" 'O IlIO, 1'OOIWtVIC,JlG . r.. J....u8Il1O_0 1M. . . . . . . . . '''"'0 .,1..," G1!,,",. f ll . fOIl1U01 11. "C'l OlIO-l0'QlT nCQ '-,,,IE Htl....." ". OZ, Ul , ~ Q 1 ~ , ~ III"1GITUI. " ,* ,"0 ' I'M.-oCMt l _ MIotoIl. ,.IM.'''' 'NU.Y , L,.,t ""'"---...g UKW-M1lICHTI H, 00IIIull oHQ . .,ItMtIr ,I '. tJ.III3 ....'IIllIlDOll .f. ,OIlu-MS.Ilon.. . . ' ~ _ ~ 3001 . . . . . . .0--_ 1"- -121) .11," ,,~ 1 ~ 1 o O l I 1 ....__ ... I ~ . ' o l l l OI , f l . ..... 0lIn. ''''OAEIl, ~ l . I . J 1 I(DUW, Til , O I I I O O - , . . . ~ ""'N', ~ ICT .I"O . . . . m .KMOlM""a100. Til t1 . . . . ,, ' l ITtIU .r,l,(l J QUI Via ~ It.1-I01)o11,1ll.Ufl). r . IOItI 11 ' '.I .Conlo CottI"or)' ' '811, W -. Ull CW,t_ .DUOILN'lGI."-"'-_ lPOOIM ~ , , _ lL 1400. ' ,0 ,eo.M.WlEUMONl. , . ., IClHttIoMIno n...,.LA' Y'Q ~ 10. "'13201 LYaAKIEII ."'*'_ S 110001SA. ~ 1"0 b ml. "IOKA"I"IIESIl.M lOCO. T. . . . . . - 22-1 ' "Ju/Io ... " '- 4IoftIo. u.. C.l .....0"1101 .0-- Cot1IIIlI. . Til N I3 .......-.. .... ' D T T . ~ " I-neol V'fl.-Ll"lGt te l , ~""""1ro: qO lM '...... , ~ ~ . K _ t\.lI'lICH, lI ._2U-'I ; ~ .lOIUCH .\/H, COt.O.II.NC4T1(lfolI. ~ l __ 110. Wlllllnglon ~ Wolllft9llln ..,.v.-.' OOIroUJNIC4T101'4 II. . . . . . . .- . . , .. 111.1 t:Q."...,- . W' ucz..1...,.. ........., 1 I T t I ' N " I . 1 t ' t " POI . Til. n. .... "'"n.o 0rrI000fI&. 'I1HIllOOVHCOIIa. L......-

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A PUBLICATION FORTHE RADIO AMATEURESPECIALLY COVERING VHF. UHF AND MIC ROWAVESVOLUME NO.9 AUTUMN EDITION 3/ 1977

I. Sangme isler , OJ 7 OH The 10 em FM Transceiver . ULM 7 0 130 142H.J. Franke. OK1PN Part 2: The ReceiverH. Bentivoglio , OJ0 F'WH.J . Brandl Selective Frequency MUltiplier! 143 151OJ 1ZBH.J . Brandl A Simple Bandpass Fil ler l or the 70 em Band 152 156OJ1ZBG. Hoeh VAGI ANTENNAS _ Princ iple 01Operatio n and 157 166Ol 6WU Op timum Design Cn ter iaT. KOlpi n Further Data lor Conslru ction 01Horn Anlenna, 16'OK 115 l or the 10 GHz BandB. Heubusch , DC 5 ex A Transceiver lor 10 GHz 168 178DUng , A. Hock , DC 0 MT Part 2H. Knauf , DC 5 CVA. Reuler Unaa r Capa citance Mater 179 1 83DC6 PCG. Hofl schildt Tha AFC Loop - A Simple and Cheap Method 184 . 188OL9 FX of Obtaining Stable VHF FrequenciesEditor No tes and Modif ications 189

A VHF COMMUNICATIONS 3/1917 129

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THE 70 cm FM TRANSCEIVER ULM 70..Part 2: The Receiver

by I. Sangmelat . r , OJ 7 OH H.J. Franh , OK 1 PN . H. BenlJ'Iogllo , OJ 0 FW

Part 1 01 this article gave a description 01 lour poss ible variants 01 this UHF FM Iranscelverlor the 70 em band (Edltlon 2/77). The concept 01 the receiver has already been 8ltplainedtogether with the block diagrams . The receiver module is used in all lour variants , wi th allghtmodUleallona lor the synthesizer version D.A photograph 01 the comple ted receiver board is shown In Flgur. II. II Is possible lo r thisboa rd 10 be u90lld on Its own , since ils audio output is in the order 01 100 mV. Some leal uresof the ci rcuit are 10 be discussed In deta il together wilh the overall ci rcul i diagram 01 thereceiver given in Flgur. 7.This is lollowed by the construction details lo r the PC-board and ellgnment Information lorthe receiver module.

2. CIRCUIT DESCRIPTION OFTHE RECEIVER2.1. Olclltl tor Ind MultiplierThe cscrnetc r must be stable enough thl t the trequency error only emcunta to one 10 twotenths 01 the receive bandwidth. e.g. a maximum 013 kHz. In me case 01 normal temperatureand voltaga fluctuation , In order to ensure that It is not necessary to keep retuning thereceiver. In principle. it would be possible to use a VFO, however. it would be very expensive.Especially Ihe temperature compensation would require special meesures. and considerablepatience and time. Onty a crystal-eontrolled oscillator is suitable lor a really reproduceableunit.In order to obtain th is in the easiest possible manner end with the grealest reproducaabillty,an osci llator circuli was selected without Inductance where the crystal oscill ates In a parallelresonance circuil. This circuit represents a compromise between switching and pulling . Inmany transceivers. oscillators Cln be found that I re diode-switched and possess ten or morecrystals. However. they are very dilticult to modulate end It Is virtually impossible to pull theIrequency using veractor diodes. On the other hand, lhere are good VXO-circults equippedwith a single crystal (1) that are so ennreuu 10 switch that It would be simpler to use a separate oscil lator lor eech crystal.The crystal frequencies are in the order 01 16 MHz and afe thus In the chel peat price range.Unfortunately. these crystals are not available with dellned Irequency-pulli ng Characteristics.The lowest crystal Irequency requi res three trequency mUltipliers (x 27) In order 10obtain tne70 cm band. Inspile 01 the bindPi SS l ill er coupling between Ihe Sliges. It is not possible tocompletely avoid spurious signals.The crystals are connected to the collector 01 the oscillator translslor T 10 via switchingdiodes . The collector current o ~ through the diode thai is connected to the positiveoperati ng Voltage via lhe 5600 reeietc r. The other diodes are blocked and are only ellective

130 - " VHF COMMUNICATIONS 311917

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' :,' nc:, IfOUfl . . . . ' I I.,.In da CIf l ulflclenl d rive II available, the pr8vioualy described baM von.g. divide, ca n be deletedand Ihe op timum ope rating poln l adjull.d with the aid 01 the lower t.al, tor and ermtterr l llo " Thia laves. number 0' componentl and results In the circuit given In Figure 4whiCh no longer requires an emitter ,...1'10' and the operating point ia adjusted wit h theba. . . .min.r rwlator ABE. A n-oatw. voltaoe 01 0.4 10 1V II generated I cro.. Ihis r raterunder drive conditiOns due to lhe baM current. This can Nilly be measured ullng highl m ~ . n e e ~ l ! I f by p(aCng I o w - e . ~ c l t a n e e RF chOtte in Iront of lhe probe . The ....Iueof ~ ' RBE ro, certain oPerallng polnt Is. of COUI'M . dependent on the f,en lillor . Thecollector circuit rs conneeteCI .. w.. thown lor Ftgur1! 3.Flgu ,. 5 ahowt th e , , * h o n ~ blttwMn the r e s i l l ' ~ value 01 Re or RBe and the outputVOltage or output power 01 the mulllphef'. The most lavorable value t. det.rmlned wlll ' llhe ' Id0 1 a trimmer poten tiometer and the next I'llghelt ....lu . 01 the Itxed rniltor i, then uMCI in theeirQJit. A ....llIe betow !hI ' optimum point could IMd to a deteriOration 01 tl'l. multlpl i .r . tl teleney due to I o l e r a ~ and temperatura .fleets.

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, \ VHf COMMUNlCATK)NS 3 /1977

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2.2. SelecUye MulUplier equ ipped wtth Flekl ft lKt Tren" alo rFigure h ~ ttle circuit Or a multiplier d..igned by DC1MK using a junc li on l ield efleetIransiSlor . Thia eircuu operates with a cer1ain quiescen1 currant and is therelore suitable formultiplication 01 low RF voltages. The Nchannel FET generates a negaUve bias vottageacro ss the reaistor Rg. It Should be pOssible to optimize the operaUng pOint by alignment 01Rg, however, thl, wa, rwttried by DC1MK.

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3. SPURIOUS REJECTION AS A FUNCTION OF THf PROVIOfD SELECTIVITYf ig ure 1 ahowl the bu ic ,pectral disp lay 01 the output aignal 01 a mult ip l iar chain. SeveralUnes will be seen on both aid.. 01 the requ ired frequency I. N ch 01dlNerent amputucle. Theirapaclng corresponds to the Input l requency 01the multiplier chain.Thia spec trum I, generated, for inatance, when a 18 MHz aignal ia doubled 10 36 MHz, and tha18MHz component Is rwt completely auppressed. The ne.1 doubler then reeelv" a 36 MHzsignallhat la modulated with the 18MHz algnal and thua generatea a 12 MHz aignal that ia Intum modulaled wi th 18MHz. and II the selectivity la not autlicient alao at 36MHz. The neddoubler then generatea Ihe required Irequency 01 144 MHz, wh ich ,a modula ted in turn with18MHz, 38 MHz and 12 MHz compOnents, In addition to thla, the harmonic, 01 144 MHz araalso pre'ent In the output algn, 1.

I I I21

' Fig. 1: Output apectlulII 01a "-qua ney lIIutl lpUar t "alt'l

148 A VHF COMMUNICATIONS 3/1977

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The German Post Off ice lays down a maximum apur ious outpu t 01 2511-W lor amateur radiotransmitters with oper l l ing frequencies 01 over 30 MHz: and up 10 2$ W ou lput power . Ath igher outpyt power 1 . , .ls. the spurious r . jectlon 01 . t I...t 60 dB Is required. For t " . r.d ,O.msteur with limited mealUrlng l acllitles. It Is ...ery Interesting 10 know what amount 01 fitt er.Ing la required In order to achieve a eportcu nd h. rmonlc slgn.1raject lon 0160 dB.Thuthor .nd DC2CV h..... worked tog . t"er to gain .xperl.nc. with mul tlpll. r chaina lorseveral pro jects . A .pectrum analyzer lor Irequenclq up to 1200 MHz: and a dynamic range of70 dB was ..... it. bl. tor th. spurious sign . 1measur.ments. The resull l ar. now to be deseneee.3.1. Frequency Doubler wIth SIngle Reaon.n' CIrcuItTh. Il,..t measurements w.re made on s IreQuency doubler chai n with a single resonant err-Cul t . t the output 01 each stag . Th. construction was m.d. as dea

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OJ 1IS ., " " on,.. .".I . H H ....JI _., ".., lu n ,II ." '" " '" '"' ''"'1_ " '" 1",

1111 ",.... r'" ,., ,., r ' '"lorFig. , : Fr.qu.ncy munlpll.r c t l. ln wlltl p.rallal and . arl ru onanl cIrc ul i ,

On allamlning lhe Ipurioul rejection al Ihe base 01 Ihe second doubler, il wal lound Ihal avery slrong component 01 the Input frequency (18MHz) was 11111 preMn" It seeml thaI thecombination 01 parallel and 18rie l resonant clrcu i t l wal not Ible to suppresl lhe input I r .Quency or the doubler sulficlently.3.3. Frequency Mu ltiplier with Two-Stag. Sandpa.. FlIt . rIn Ihe mean!ime, DC 2 CV h.d ConltruCted a frequency multiplier chain Irom 24 MHz 10144 MHz using two It'Q81 l imU. r to that lhown in Figure 3. A capac ltlvely coupled two-It.gebandpasl l ilter il used lor ..Iactlvlty. The Inductances .re enclosed In Individual screenedcans which .re screwed on to copper eoetee ground surlace, which 18rv.1 It grou nd lorthe whole circuit. The lPurlOUI rejection of over 60 dB W.I achieved Ullng thll conetrucncn .Atter this success, the author .110 modilied Ihe l irst two doublers 01hll circul i lo r bandplSI!ilter coupling (Flgur. 10). Although the Inductancel were unl creened end were mou ntedsimply on a copper-cc. led bo. rd, .nd allhough the grou nd conditlonl w.re moal certainlynot so ideal as DC 2 CV's const ruction, a spurious rejection 01 over 60 dB W.I allO mea.ured.Figure 11 shows the bal lc Inl tallatlon 01 the multipl ier ch.IO In TEKO boll type .. A. The18MHz crystal and uaoclated trlrhmer are mounled in the bottom lelt-hand corner. A VXOand VOltage ltablllzer c: ircui! 'or 7.SV are mounled beside thi, . The d..ignation l VI to Vpshow the positIOn ol lhelranlislors when the circuit Ihown In FIgure 10 II uNdoThe pOl itlon01 the Inductances II given In Ihe term 0' circl... The ground l urlace runl around the edge01 the board Inclu(hng the VXO.Wilh th ll aUlhOr', prototype, the lu I doubler wu not modified lor bandpaaa Im.r coupling 10that the board did nol need to be modif ied. Due 10 thil , the 72 MHz compOnltnta wereIlronger than neceaaary In Ih. output l ignal lpeclrum. H o w ~ r Ih ll wit not 100 Importantsince they will be suppretHd by lhe 2 m bandpass l il ler (1) at the output of the tranamitter.BandpaSllllter COYpling will be used for all lreQuency doubler atlgea for luture conllrucUonl .

- 148 0\ VHF COMMUNICATIONS 3/ 1911

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If one compares the liller circuits 01Figu res 9 and 10, it will be seen thai only two exira capaci tors are actually requi red. How8\'er, the circuli 0' the second bandpass tuter stage with II Icececruve Input and output co upling Is l ar mora llul lable lor suppressing lrequaneis l belowthe required harmonic than a series resonant circuit. The good result obtained using teeeebandpass l illers show, how Important It is 10 auppraS!l the Input frequency 01 the lrequencymullipller Ilage In order 10 obtain 8 good spuriOUll rejection.In orde r 10 slmp li ry the daslgn 01 the band pass l ilta, l or any required frequency, Flgur. 12shows 8 frequency-independent diagram where the capacitance values are not given but thei rreacnve Impedance. The requ ired value l lor the application in Quest ion can be calculated' rom tneee valun . The InductanCll! should be designed lor resonance. This circui t is valid lorope rating voltages in the order 01 10 V and lor currents 01 approximately 5 mAoA capacitive current divider circuli Is used lo r coupling the subsequent bipolar transislor ontothe seco nd bandpass liI ter circuit . This means that a part 01 the resonant circuit current IItapped ofl and l lows through the trsn sistor Input. This leads to lower capacitance value thinwill be present with the cepacltive vollage divider and the lower capacitance can be verylarge under some conditions and posses..s I consldereble intrinsic inductance.

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4. DISADVANTAGESOFTOO LOW A COMMENCEMENT FREOUENCYTo finalize, the dlladvantages 01 using too Iowa commencement frequency lor the trequencymultiplier chain are to be discussed. When using Ine.:;penslve 9 MHz crystals, the l irl tspurious line above 144MHz lalls Into the business radio band and can be sufficiently strongto cause Inter1erence to neighbouring buslne. . radio . yl teml . A few Individual cases 0 1 thisheve been known when using an Inlermedll1e frequency of 10.7MHz. It may be good prectlceto use even a three-stage 1iI1er for the first frequency multiplier In order to suppress theadjacent spurious lines.A turtner disadvantage 01 using a commencement Irequency of 9 MHzwas lound when constructlng the 70 cm repeater DB 0 TR 1'1 Rosenheim. Since the spacing between transmit andreceive trequeneles using the European standard amounts to 8.5MHz, the l irsl spurious line9 MHz below the transmit frequency overloaded the receive con verter. This problem wassolved by modify ing the Irequency multiplier chain lor a commencement frequency 0 1 18MHz,

5. REFERENCES(1) H.J. Brandt : A Simple Bandpass Flltar lor the 2 m Band

VHF COMMUNICATIONS

LINEAR AMPLIFIERS for 2 m and 70 em

Dealers enqui ries welcome toUKW-TECHNIK Jahnstr ,1406523 Baiersdor1(W,Germany)

Clean linear operation due tooptimum biasing and use 01CTC transistors BM 70-12 orCM 40-12 resp.BandOutputInputCurrentSize (mm)

145 MHz 432 MHzSO W 40W10W 10 W10 A 6 A130.:; 56 .:; 200

U K W TEe H N I K . Hans Oohlus oHG08523 BAIERSOORF . JahnslraBe 14Telephone (09133)855,856 . Telex: 829887Bank accounts: POi tsche

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A SIMPLE BANDPASS FILTER FOR THE 70 em BANDby H.J. Brandt, OJ , ZB

t . IHTRODUCT ION

Th IIltar operates acCOrd,ng to the ..me pr ,roc,pIe the 2 m bandpaa lo iter OttICribed lfl( 1) SlflCe the ,lomen5lon. 01 the cu e . r . conlldet".b ly mo f.vor.bIe IOf the 70 em b,lrod.better frlter chlractenst,C& IF\lro lhe 2 m vef"SlOn wet, 10 be e.peeled HowevI_. th,. ' . roOIcom ptellly lrue In pracllCI

t .t . Loc . tlon of the ConnK1o,..It w found when conllrucllrog thl f i r " pro totype thaI II wu root poulble lor thl conf'OlC lOI"Ito be p lacid anyw-he.e .eq ulred . II reproducible cha'acteri. hcrl to be ob tained , Furthermore. thl narrow .ides 01 thl boll arl no t IIrong l roough lo r thi . For Ihi. realOn. 8NC.connec tors with lIange should be uNCI . which .re Ih.n mounled o ro the ba.. pl. t. 01 thelilter boll .1.2. S p u r ~ u I R. aon. ne. 1Line cl rcultt .lways ha........... .1 tIIOn.nces . Wllhoul C.paCltl.... load . such reaon.Inc.. willoccur a l .11 odd multip'" 0 1 '1.. / 4 In the c... 01 Ihl 2 m bendp... l,lte r Ih. Io l"lt .puriou.r. aon. nce was in ellcesl 01 1 GHl due 10 th. Ia'ge C.paciti. . . . .ho rtening 01 thl line eucou..nd wa. Ihe.elore 01no import.nce.In the c... 01 th e 111"11 prolotype of fhe 70 cm l01I. . . Ipprolllmltely the ..me hne length w uNCI .. on 2 m but the capac ltl.... ~ wu r e d u ~ The Ill"It spunous ~ wu Inthe orcMf 01 1Xl1)MHz . in other wordl . t the thlrcl harmonic of the 70 cm blind , It wupoulble Ullng a low induetl\l9 groundIng 01 the Inmmer cap&Cllors IOf th.S r.aonance 10 be1h1"1d 10 apptOlumalefy 1700 MHl . whICh II in lhe order 01 the fourth harmonic. A1llnemptt10 tuppr... thiS spurious ~ I ~ were wllhou t 1Ui:c... In the c u e 01 thIS Simple. I ) ' m ~trical '.Uer construction . In order 10 ensu,e tha i IhiS r-.onance wu II IN.t berw.en lhefou rth and IItth harmonic. 11 WII only po",ble 10 ' Ihe in,.,., Conduclor 10 be Ihorten.cl' ' 'ghtly and to accep t I t1ightly higher InNrtion lou .

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2. CONSTRUCTIONThe u me l i ......rpl. ted OOK I, used lo r Ihe 70 cm Il l le r a l lor the 2 m 1lter delcr ibed In I t ).The dim llfl l ioo l are 94 mm K 50 mm K 25 mm hi$lh. The loee lion 01 lhe panl II given InFlgur . 1. The two l ine circuits are constructed from 2 mm diameter, silver plated copper wire.For . bandwid th 01 10 MHz, th ey are spaced 16 mm from another . Tha Input and cu tcc tcoupl ing is made ul ing 1 mm dia . silverpla led copper Wire. This input coupling i l piecedfrom tne Input Or output eocket to me 50 0 pOll tlon on Ihe resonant l ine, where It Isso lde red Into place. A emeu coil (3 turns , 3 mm inner diameter, epprnx. 4 mm long) II to befound et one end 01 the inpu t and output co upling that is solde r8(l to the inner conduc to r o tthe SNe connector. These inductances represen t fillers lo r higher frequenciel.Silver. plated solder 'ags are uSftd lor the lowinduc t,ve grounding 01 the trimmerl . These taglare screwed to the base plate and bent back over the nu l as anown in Flgur. 2 Alte r th ll . thetr immers are mounted InlO place . The conneclion 01 the rotallng plelel is then connec ted tothe bent so lder tag and soldered tote place.

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The co ld end 01 the tine ci rcuits Is I lig htly lIa llened and placed Intc bent sllverplat8(l soldertags. These are held in place by the inner mounting screws 01 the BNC conneC IOrl. The linec ir cuits and solde r tags are then IOldered together. The l pacing between l he tw o line c ircuitsI I adjusted easily by bending the IOlder tags a l required. The ~ u l r e d noles in the base plat.are shown in Flgur. 3. and Flgur. 4 gives Ihe poI itlon 01 the alignment ho las in th. coverpla le .

2.1. Main CompOn. nts1 Filler bOK, silve rplated , type 94 .60.04 Solde r tags2 air.paced trimmers 5 pF lor ch usis mounling2 conial socket l type BNC With I lanoeSilver.plated copper wh.. 012 mm dia and 1 mm d,a

~ VHF COMMUNICATIONS 311977 . 153

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Th, same .Ilgnment method ahould btl uMd a. "I" deterlbed lor th, 2 m bendp.lu liller in(t l. Figure 3 shows the Ml.cUvity curve m H a U r ~ on a . _ p t l ~ u e n c y Iptem whenahgn.a lor mInimum VSWR In th, range 01 ~ MHz to 440MHz. , ~ . , \ VHF COMMUN ICATIONS 3 /"77

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V-, , , , ,

.,

fig . I : Phalogrlpll 01_ 01' " 'e lu ll'lOr'1 prototyp..As can be seen In Flgur . 5. Ihll lecond and third ha rmonic Of Ihe 70 em band Ire aupprlllllldby mere Ih an 50 dB. Sulficillnt luppreslion is also given tor tha lourth and fi fth harmonic.These . r . dependant on the spu rioul ronanC8 81 1900 MHz. which will be ahilted somewhatIf Iher. are any dlHerences In Ihe mechanical ecnstrocuon . Th18 11118f represenlilhe optimum01what can be Obtained with mll'al plate and wir .Spurious resonanc have been I problem with .arli.r publlcationl and deSCrIptions 0' lillef'with fl lson ani l ine. (Relefences 2. 3). The rejection in C I l S l 0117 00 MHz could only be imprOVed by providing I coax ial low-pass l iller with . cut-o Il freQuency in 11'11. order,

~ VHF COMMUNICATIONS 3/ 1971 155

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It will allO be seen In Figur. 5 lhal th. utter also luppr..... an lubharmonlCI 01 th. 70 cmband , as ...... 11 as any un .....an ted harmonics 01 the 2 m band Th il advantage 01 1'1. bandpasaIiI te r ..... '11'1 respect 10 a lo .....pa.. nner is especial ly impOrt.-nl lor tranlmillers usIng aIrequency multlplicahon princlple . In crillcal Iccahons, the auppr...ion 01 tha TV b,lnds IIIand IVIV could be 01aulslance.Th. Insertion IOU 01 tha 1lt. r amounls 10 0,4 dB . Th. 3 dB IrltQuancies ara In lhe order 01415 MHz and 450 MHz. A pho tograph alone 01 lhe authOr'a proto lypes i l givan in F1Qu,e t ,

4. REFERENCES(1) H.J. Bra ndl. A Simpla Bandpass Fitter l or Ihe 2 m Band

VHF COMMUNICATIONS 7, Ed/flon 411 975, Pages 244.249(2) H.J. Dohlu l : eoaxial LowPass Fil lers lo r VHF and UHF

VHF COMMUNICATIONS 2, Edition 3/1970, Pagel 166 t7S(3) K, Mai .....ald : A Bandpass Filter lor 145 MHz using PrInted InductanceaVHF COMMUNICATIONS " Edilion 411969, Page. 205.208

NEW I NEW IPOLARISATIONS SWITCHING UNIT for 2m CROSSED VAGISReady-to-opera te as deSCribed ,n VHF COMMUNICATIONS, Complele In cabinet ..... '11'1 threeBNC ccnnectcre. Especially de'lgned lo r use Wll h c rOlsed yagls mounled a. an _X_ , and fedwll h . qua l-I.ngth leed81" . FollOWing . i .. polar isation. can be tel8(ted : verneer. bcnzcntat.Clock ..... lse ci rcu lar , anllclock..... I Circula r, , lanI45 and slant 135 ,VSWR: ma... 1,2Pow er: 100 W earnerDimensions : 216 by 132by 60 mm ,

Insertion 1011 : 0.1 10 0.3 dBPhase error : appro ... 1

156 -

U K W - T E C H N I K . Hans Dohlus oHG0-8523 BAIERSDORF . JahnstraOe 14Telephone (09133)855.856 Telex: 629 887Bank accounts PoslKheck Nurnberg 30 4M Meeomm.rzb.lnk Erlangen 82001154

~ VHF COMMUNICATIONS 3/1977

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VAGI ANTENNASPrinciple 01 Operetlon and Optimum Design Criteria

by O. Hod l, DLI wu

Vagi antennas are well known In the VHF and UHF l lald since they .lIow directi onalantenna with relllsonable gain to be obtained In a I lmpl. manner. However, one " olten disappoInted with home-made Vagla. and 8'1' 1'1 sometlm with tho available on the mark el .Thla arti cle is to show how design errOr, can be .void..:!, and whi t performance " 10 beexpected .

1. UNIFORM VAGI ANTENNASThis type 01 antenna was origi nally descr ibed by H. Vag i In 1928 (1). and pOl lU lIed ne. r ly all,.... leafu,es of mo

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The delay component of an element and tne current enarglZed Into It ara beth allered togetner witn Its lengtn, wniCn means tnlll two demands are opposite In tne case 01 longantennas: In order to limit tne pnase snil l , it is necessary lor Ihe element s to be shortenedu nt il l in al ly no noti ceable current Is able to Ilow. Tnis means thaI the lengtn and gain 01 aYag l antenna Is limited.Ehrenspeck and Pt)hler , as well as meet 01 the other antenna specialists. ellamlned unllormVag i strvcturee. that Is antennas having constanl director spacings and lengths. The lollowingcan be summarized lo r Ihls type 01 antenna :1. There Is an oplimum value 01 the pnase speed and tnus the tOlal delay 01 the wave Irontlor each antenna leng th. The most lavorable delay increases with Ihe antenna lenglh. how ever, only up 10 a value 01 apprOlllmalely 105- or 0.3) , . This is oblained al an anlennatength between 3 ) , and 4 ), and remains ccnetant tcr longer anlennas.

2. The phase speed V along a dirK tor chain Is dependent on the lenglh, Ih ickness andspaci n g of Ihe elements. The,e ara an Inllnile number 01 combtneuons Ihal lead 10 Ihemost tevcrebre value of V. When using etement spacings of 0.4), and lass. me samemell imum value o l lhe gain witt be achieved .

3. The mexfmum gain possible is only dependenl on the anlenna lenglh if Ih e mos l lavorablevalue of V has been obtained.

4. No noticeable gain Increase will be observed at grealer antenna lengths Ihan 6), : themaximum gain value of a conventional Vagi stru cture is in Ihe order of 14 dB. Flgur. 2shows this relationship, as welt ss measured values 01 several anlennas available on lh emarket . and also some hom e-made antennas. The number given In the designation givesIhe number of elemenls.

I D- -,:,: : ~ - -. -0 --, ~ - - !.- -~ . . i. 1-- : ii: I - - ~ ? i" V / f/, /

O6wu'" - ,Fig. 2: a . ' n of l . " l .nt.nn..... function of th.lr I.n"th

m...ur....." ! ' : DL 1BU; 0 D L ' WU 158 . \ VHF COMMUNICATIONS 3 /1977

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2. NON-UNIFORM VAGI ANTENNASSince the above Information II valid for uniform Yagl structurel, Ihll led to eltperlmenlationwilh non -uniform entennal to obtain fUrlher Improvements, Due 10 the large number of parameters. further eKperimentallon Is very dillicult However. II has been found thaI II Is morefavorable for the delay to be concentrated In the vicinity of tne radiator and Ihll to bereduced tcwerce the end 01 Ihe anlenna (3. 4). The curren f ccmccnent of Ihe elementlshould also be reduced logether with Ihe distance from Ihe radialor (4). Bot h effects cen beoblalned together when using a continuous reduction of Ihe element lenglhs and Increase 01Ihe spac; lngs.These measures have Ihe effect of reducing the minor lobes and widening Ihe main lobe withrespect to these of a uniform Vagi anlenna. Mu imum gain Is oblained as a compromisebetween directivity and suppression 01the minor lobes.It Is also necessary for the disconiinuities al Ihe open end of lhe sntenna and al the radiator10be COmpensaled since Ihey can lead to interference elfecls on the travelling wsves Ihat areprevalent wilh _lIodeslgned antennas.II Is true that lhe above considerations have been part ially assisted by compu ter slmulalion.however. It has been found that further eKperlmentation is alwaya necessary. For this reason.the proved knowledge about unilorm antennas. which are a good epprcxtmattcn also for Ihemean values 01non-uniform antennas. are eKtremely uselul lo r use as basic values.Even Ihough, it seems that the maxlmum Increase in gain to be eKpected Is apprOKima tely1 dB . over that given by Ehrenspeck and POh ler, even atter all Improvements have baanmade. This means Ihal the maltimum gain Ihat can be achieved with a single. conventionalYagl entenna. should not be much higher than 15dB.This shows Ihat ed ram" eeutrcn Is required when higher maximum gain l igures are given Insome publical lons. e.g. (5, 6). Usually these are then gain figures Ihat have been calculaledIrom the beamwldth. or values Ihat have bean falsmed by ground reuectroo. Errors In Iheorder 013 dB are Quite common. Gain measurements are 10 be discussed later In Ihls article.After completing the manuscript for this article, the Information given in (9) became available10 the author. In this article, controlled end reflection was used 10 obtain a furthe r, smallincrease 01gain, however, the design seemee to be very ermcer.

3. HOME CONSTRUCTION OF YAGI ANTENNASHome ecnatrucucn of antennas Is Slill vary r_ardlng, especially when large antenna arraysare to be constructed . Model anlenna systems on the 70 em or higher bands l implify thedesign . and the final results can be recalculated for the required Irequency. However, anyonewho wishas to const ruct well-known designs, 10 modify them, or 10 recalculate Ihese forether Ir, quencies should know Ihe allec t 01all construc tion parameters on tha operation ofthe antenna. Seemingly slight deviations can cause a complete lailure IThe lmpcrtant dimensions are: antenna length. element spacings. elemenl lengthS. elemenldiameter, and also the thickness ol lhe boom,

... VHF COMMUNICATIONS 3/ 1971 - 159 -

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3.1. Elem enl Lenglh end Olem ele,Figure 3 Ihows the dependence 01 lh e elemenl lenglh e l e lunC lon 01 Ihe element dlemelerlo r re llector , redieior end dlreclors (meen velue lo r en directo rs). when lh e Olher dimenlions01 Ihe antenna are elready kn own . It mey be surpriS in g 10 Me tha i u II not Ihe an lenne lenglha n d e l eme nt &pacing Ihal II used a l paremele r bu t only Ihe number 01 elements.The reason lor Ihis is in the reciprocal releUonship bel_n Ihe phase delay and elementspacing (1), Since the meet lavorable del ay remains precllcetly con,l ln t wll h long anlennas(as wes al ready menttonec in secUon 1). the curvel for tne same number 01 elements coinci de , Th l' I' no longer valid lor I hort an tennas ( ::Iii 1.52) bU llhe app rOlllmation II uselu l In allcases.

'"

, I II /'" , 1 k~ . -:e !I- = I --

I11/ II I -' ' ,-II tt - I-i- f - 1- 1-I I[:k /7 I I1 -, - 1-1 , ~ - ""~ / - .

V 1// -/ / / / Ii-- / /.-

"L "'I , I / />I """I"/ ~ Df. nttt -" I-~ -' -I--! a '"i I

"

"I'"'"

. 160 ~ VHF COMMUNICATIONS 3/1977

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II will be seen Ihal the . I . m . n l diamelar dependence ol l ha dir.Clor lenglh i n c r e a N ' wllh I h .number 01 elements, and i , la r greater Ihan Ihal 01 the radiator and reI lector _Thl' L' becauNIh . radialor and r.flector are r.sonant circuit, ope rated Virtually in resonan ce, whereas Ihedi rector, are IIrOngly detuned capac.hv.ly , On incr.a,lng the dlame l. r , lh. a will d.crease.which mean, th .t lh . oeluning mUSI be lu rther increased in order to oblain Ihe um . phaNposi tion. When using Ih. Mmi-Iogarlth mic scal. used here . il i , .asy to see Ihat a ,hortenlng0 1 approximately 7 % in lh. cas. 0 1 the radia to r and reuectcr and approxima l . ly 14 % In lh.case cttne diracto, . is requir.d when inc r .asing the . I .m . n l diamet.r by t. n l im. . .The curves 01 con ,tent reectenc e 01 an individual dlpote etement. as tak. n Irom an anglneering tab la, are given In Figura 3 a , dashed lln.a . Th . ,olld l i n . , are experim.ntally derl ...edcurves 0constant el.ment perto rmanctl, It wUJ be seen Irom Ihe gre.1, imilarlty in Ihe curvelhal it is mainly ilS reaClance lhal la import.nt lor the operation 01 an . le m .n t. T hi ' mean,thai when it ia r. placed by an .Iement h....lng a dl llerent di.m.ter, the original reactancemust be res loted, The real componeni 01 the impedanc., e.g. loIS and radialion resi,tanc.,have a v.ry amall d.pendenc. on lhe length and diameter in the ...icinity 0 1 ).12.The lenglh ld lamet. r diag ram is Ihe r . lo r. . . . .ry advan tageous wh. n m .king calculation, lo relements 0 1 d il l. r ing diameters: th. valu .s 01 langth . nd di.m . ter (I" d,) should be lound lorlh e know n elemenl , through th is point anOlher curva " Interpola ted parallel to the n.a reslcurves given in Ih. diagram and the new values lor the diamete r dt and leng th I, read 0 11 all he required poin t.Jl the element lengths diller nOliceably. this c.lculation must be m.de lo r eaCh elemen l . It "usually .u lliclen t to calcu l.te th. dll1erence between Ih. old and new .....r. g. I.ngth .n d tocorrect the indlvldu.1 .Iern." t leng ths correspondmgly. By the way. the length tol.ranc. 01 .nindividual .Iemant is relatively la rg . a . long as th. m n v . l u. is m.in t.in.d WIthin abOut0.5%.No sig nllican l ettect ol thI.m .nt di.meter on tne gain cou ld be observed Wth antenna, upto .. ),. DI. metel ' l l rom 0.003), to 0.015), were . ...mined . However, a 1011 0' gain was observed wi th very thin bra n .Ieman ts. which was prob .b ly caused by skin . If.ct losses.

3.2. EHec t of tha Boom Dlam . la rVi rtually no infonnahon can be found on the .lfact 01 thlem.nt mounting. Som.tlme. It ismenucnec that . pproximately 2/3 01 the boom diameter thould be . dd ed l or .Iements I h. tpass through a metal lic boom .Experiment s were li rstl y made by comparing calculated and measured rason.nc. pOSlllons 01varl ous an l.nn a, in order 10 obtain tha requ ired Inlo rmation . how....er. thi , was really inacc urate and only showed a gene ral tendency.For thi s reason. th. author dec ided to carry oul h i, ow n measuremants. T h. daluning 01 amatched Ih ree-elemenl an t .nn a on alt . rlng Ih . d la m.t. r 0 1 the (long) boom in Iha Vicinity 0 1the dir. ct or was compensated lor by reluning the di rector . ThiS reaull.ci in th. curve gl ....n inFIgura 4. whICh ahould be ,ufllcienlty accurata lor praeltca' application . No .lIeel 01 theshape 0Ih . boom (ci rcula r. rec tangular, or U-shaPltdl could be found Tna elament diametarseem. to ha.... linle Inllu.n c . a , long as n remains below bOOm dl.met.f .

~ VHF COMMUNICATIONS 3 /1977 - t61

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.0].,

'. or /.OL 6 WU /0 U V -

./? V /I 0.0) . /i> ~1%/.. V /on

/ V.. //Ul, / ./----V "'P"-

t!lf

Fig. 4: Inllu.nca 01 m.I.III1:: boom on r..on.nt I .ng lh 0' , I ,m,nl t pl.r

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Two simple methods have been proved in practice: the antenna to be op timized Is used astransm it anteona connectecl 10 a very long teeeer (3 dB loss or more), or IS receive antennaconnectecl to a good terminating resistor . In both cases. the antenn a Is tr immed lor mextmumreceived voltage. The fine sllgnment Is then made with the aid 01 a reuectcmeter. il reQuired .In th is way , it is not poss ible lo r the antanna to be matched co rrectly, but be comp letelycetuneo .3.4, O. ln Me uremen t .axect measurements on antennas are very d il l icult, especi ally gain measurement s, Thedemand s made on such measurements are given In lEC 138 and DIN 45003. Especially themeasures given in this standard to avoid interlering ground reuecnoes are usually completelyIgnored In the case 01amateur measurements. Usually , II Is only poSSible lor us to be able tomeasure the matChing, and the horizontal po lar diagram, e.g. the Ediagram in the casa o fhor lzonlal po larisation. Sinc a Yagi antennas possess a relatively close relationship betweenthe E and the Hdiagram as can be seen in Figure 5. this allows a certain cri terion lorestimating ttle gain. II the measured values are. however, placed in the gain nomogram (6),one will obtain a theoretical upper l imit of the gain , but these values are most certainly toooptimisti c lor practical appltcatione. since the diagram anumes no-loss antenn as with outminor lobes. It is especially with very long antenn as tha t the minor lobes Increase with lengthand thu s the losses,

,

O'Dl 6WU\ ,\

'\ 1of- l \ \""-'"~,r - ~ ~0.

ltng lh _o10

)

,5,9

'111, 5: B..mwldth 01 Yagl al'llann .. a. a '" nc:llon of thl anlll'll'll 111'IfI11I(mla n ",.Iu Irom num.rou. rallrlnc:l. and ma.."red ",. lu..). \ VHF COMMUNICATIONS 3/ 1977 163

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3.4.1. ENect of 1M Minor lobel on t/'I. OlinThe b" i l 01 III g,lin " l Imit" l a k ~ Irom the polar d'lgram '1 thl bumwldlh 0 01 th . m'lnbNm (Ingl. between the 3 dB potnll). The a n l ~ n l il then . . . .umed to be In the c ~ t a r 01 a~ Ind !hII rlhO 01 the surface ll1umtnaled by Ihe main beam to Ih t SUrflce 01 Ihtc o m ~ I ' tpIWfe (iKllrop iC rad.alor) II . . tablilhed In lhe caM 01 the ume Inpul power. andneg llg.ble minor ~ !tie ga.n COIncKMIto 1M rKlprocal of the surfKe ratIO.S l ~ the energy flOw denSity II not constanl w.lh ln lhe ma.n IDba. correchons will berequired lor trw . I l K I ~ surfac. arM according to ' he auume

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Since P PH + PN i l conilanl . only a corresponding ly reducad component 01 the tOlalenergy ' I available lor tha main beam, and Ihe g l in will be reducad to the some reno.The dec rease in gain amountl 10:

GR -Wilh ou r example wll h SN/5H 5.6. Ihe following .1 vllid :

R5.6 (7.5 dB)10 (10.0 dB)20 (13 .0 dB)50 (17.0 dB)

2.0 (3.0 dB)1,6 (2,0 dB)1.3 (1.1 dB)1.1 (0.5 dB)

II will be seen thaI wh.n the minor lobe suppr.ss ion II only 7.5 dB . 1 In thil c. . . . h.11 Iheenergy will be -10$1- In Ihe minor lobes and the maximum gl in wilt be reduc.d by hall.It one a. ,umes Ihe tenowing data lo r the prototype antenna: " E " H 24, and NN 13 dB, lhe lollowlng gain calculaUon will result:

Gi 55 ,7 17,5 dB (ral. Isotropic radi l lor )GO Gi - 2,14 dB 15.36 dB (reI . dipola)GO reel. GoIR 14 .26 dB (ref . dipole)

This valu. coincides well wll h the measured gain values 01 long V.g l anl.nnal . For clarihcalion, II should be noted that the above . ...mple i l very typical , howev.r, lhe poI.tlon andwidlh of tha minor IObea vary. Tha tendency ii , howaver, very cle lr: the a!tact 01 the m inorlobes inc reaMI together with the dIrectivity. II II also nOI polllble lor Iha back beam andhigher-order minor lobea 10 be alwaya neglecled.Precl icel .xperience gained l ince l irslly writing thil art icle t.nd to indicate thaI the glin car-culaUon acco rding to the Tal/Pereira axpr...ion (8) ara IOm.whlt lew . The glln formulaaccording to Kraul given In the l ame paper IG 4 I t ("1 x ",) ] aeemingly coincld.1 with Ihemeasurements more accurlle ly, In the above exampl ., GO red . would be 15.34 dB.

When plotting the polar dlag rama and making comparativtl anlenna rna.auramanll, It la varyImportant that a good mllchlng 'I made. MOi l racelver Inpul l cau... conaidarabla mllmllchto the l eedar wh ich can cauae a detuning ettect on Ihe antanna wh. n uamg tho rt leederleng th . This can be avoided when ualng a 10 dB all.nualor.The au thor used an e x p a r i ~ n t l l arrangement lor tha pr.lImlnary ellparlmarola ualng analuminium boom of Ulhaped prOfile. The .Iement l w. re told.red into brall blocka andcould be Ihlhed along tha boom. The dim.nsloos ara v.ry handy wharo l h... allperlmerolliremade in the 70 cm banci. Tha datennined lenglhl and lpaclnga w.,.. than Illed in a cardIndex .

, \ VHF COMMUNICATIONS 3 / 1977 165

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T.. larg. relllctiOn lree anlenna m.uu ring range 01 Ih. German Pa.t Office wal ~ I I " , ".vallabla lor act measu reman t . A typIcal e.ampla I. !hat a 2 long unilorm Vagi con.Ilructed according to data given by Ehranspeck indica ted a ga in of t t .O dB .nd Ihu. Ihoweclonly. devlalion 01 0.15 dB Irom I " nomina l valu. given In Figur. 2 A 1l)-elemenl Vagi 01I" ..ma length derived lrom this I/'lOwad a gain 01 11.5 dB wIth a tlMmwidlh Increaa Irom34", wllh mInor lobe IUppreuion inc, . . . . , by neerty 10 dB. In e o m ~ r 1 M M ' a sariel producedanl...,na av.ilKlle on the market of twICe the length only prootlda

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FURTHER DATA FOR CONSTRUCTION OF HORN ANTENNASFOR THE 10 GHz BAND

by T. K6lpln, 0 1< 1 ISSevera l mechanical dimensions were gi ven in (1) lo r the construction 01 horn anlenn lorthe 3 em band . Construchon JU lt using lhe.. dimensions 'I not Ilmple. several other value,are rfIQuired lo r cun ing the pialII' and bending . The,. velu. . .re 10 be given in the lollowinglable. They are bliNd on Information given in (1) and are thu s valid l or a me. n ope ral lngfrequency 01 10,3 GHz. The 'eed 'I mlde With WR 9O-wavegulde. which has the Innerdimension s 01, .22 .86mm, b - 10.16 mm.

SilM 8 Lenulh L He;Qhl HA He

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A TRANSCEIVER FOR 10GHzPart 2

by 8 . Heubu.eh, DC 5 ex .Dr.ll\9 . A.Hoek, DC GMT H. Knauf, DC 5 CY2. GUNN OSCIlL\TORThe microwh'a oteill. lor IS the mai n module 01any . n ~ ...., lor the 10 GH: band . In ord.r10 OOI 'ln long . hne--ol'liQhl pallna, 10 GH: a N C e l ~ .r. practIcally only lolled in lhe certable moo . ThIS means lho1t only ban.,. . . elin be uM

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11 a Gunn element i. placed in a sullable position in the r. lOnator. It w ill lnergize lh i.oscil lat ion . The resulting trequ. ncy I ' primarily d.l.rmined by Ihe geometric dlmen ' lon . otthe cavity. The capaCitances . nd induct.nc.s 01 th. Gunn .Iemenl alao h.ve certain , butrel8lively sm.1I effect. Since th... are d.pendent on thl operaltng vonage. th.y can be u..dfo r erectronrc tuning 01 the oscillalor. II the oscillator i. to be woee ove' Wider Irequencyranges. It wil l be nec.ssary 10 vary the dim.nsion. 01 Ih. re. onalor. Sinc. Ihls I. dlll lcu llmechan ically, It Is usually the e c i m . n s l o n s that . r . alter. d, lo r examp le, by InsertIng metal pin . Thi. incr..... Ih. induc tance or the reBOnator ; iI , on Ih . other hand, adi.lec tr lc pin I , inserted Into Ih. resonalor . thl, wil l . It.r Ihe capaCllanc . A chang. 01 Ih .relOn.nt Irequency ot the re&Onator will take plac. in both c.ses . Exper imenll have .hownth . t when u.ing metal ICr.wt for tuning th i t can often lead to frequency Jump. dUI tocontact d lff iculliet to the ouilid . 01 th. caVity, which can only be avoided when uting arather .xt.nsl.... construction. T.Il on (PTFE) ICrttWI h.ve been found to be v.ry . uitable. andeucw very clean , conllnuou. tun ing With high r.produClbility . The lOst ot other plaaUcmaterial, II usually too high and the oscil lator will etten not .v.n olcillat .Flgur.. 12 . nd 13 ,how. Gunn oscillator cons tructed according to this pr inc iple. Il l. basadon a recommendation of Or, O. ln E....n G 3 APE,

One of the two conducti.... walll has been removed and formt an aperture (Iri.). throughwh iCh the AF-eoerOY il fed to th . w.vegu lde. Th. MCond PInel i. v. r iab le and I. uMd loradju.tlng the resonanc.. The dlmenaion. ar. cr itical. and any d.viatlon. can cau.. largefrequency d....iatlon . Th. r . lOnator can . Ithe, be made 'r om a piece 0 1 wavegu ide orsolder.d tog.ther from ind l...id ual pieces 01 brass plate. The lafter II somewhat d llflcult due tothe large amount of tolder lng , The metal lic mast of Ih. rnona tor .hould be grea t ..possib le In order to ensur good ahort- term "ab ility with 'espect to temperature neetueuoos.Since Ihe Gunn elemen l I. eXlremely low .impedlnc. in operation, II virtually r.pre..n l l I.hort-Clrc;uil lor lhe wavegu ide. Ttll, me.nl tha t it mu.t be vIrtuall y mounted on Ihhortci rcuit pan.l . Sinc. th l . I I nOI pou ible for mechan l t, l l and .Iectrical reaten., th. d.tcr lbedA VHF COMMUNICATIONS 3 /1977 - 169 -

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cavity resonator has a length of one complete wavelength. The Irequency-oelerm lning lengthis now the spacing between the panel and Gunn element. In practice , It has been found lhalit Is advisable to keep this distance IOmewhat smaller than given In Figure 12.

JCounter ny! MS

Ciunn , l ,m nl

PTFE d,u

2 '.,1: : t,'.,. -+

PTF( d,sc2 5 ~ n n 'nlo pili "

--,---,E]=::j9l>-i--,J _Waveguide f lange2 Diode holder

J Tuning pin4 Shor t-circui t piston5 Iris

F1g. 1S: Qunn o ,e lll,tor 'nd eonllNCtlon

Tha Irequency is then somewhat too high and the requ ired frequency can be adjusted using0.5 mm or 1mm thick brass space, . between Ihe Ilange and trte. These space,. must havethe same shape as the flange. II Ihe Irequency Is 100 low, a ccrrecuce II virtually ImpossIblewith normal means. In this type of construction, the ehert-clrcult piston has little el lect on thefrequency 0 1 oscil lat ion, but has a great elfact 00 the output powe, . For practical operationlater, It Is better that the piston be replaced by a f illed short-circuit panel at the correctposition.The following is Important lor mounting the Gunn element:One connectIon Is grounded , normally the minu. pole ; the other connection must be connected to ttle elllernal operat ing voltage. Thl. Is usually fed In in the form of a bypass

- 170- ~ VHF COMMUNICATIONS 3/ 1977

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AsUc,.,.JT.

~.

ifdi

IlpaI

"-,

-lO-

r-

,.

,

tenatran6

"

s

""--.

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ceceencr. whose dielectric Is thin pla lt ic IoU; PTFE (Tellon) II recommended . Since theGunn element can oscillate together with any Inductance, e ~ t e r n e l Inductances ere verydangerous, I ince parasitic oscltletion cen oc cur at conl iderebry lower Irequencies. whichcould then deslroy the erement. For Ihl , reeson. the oacmetor should be bypassed withlow-inductive disc capacitors direclly edjecent to the Ol cHietor.

3. POWER SUPPLY AND MODULATIONAccord ing to the menulacturer. and the power raUng. Gunn element l requi re operallngvoltage, In the order 01 7 V to 10 V. This voltage should be stabilized since any varialion 01the opereling voltage will cause nuctuationl 01 the output lrequency. II e banery vollage Of12 V is available, a simple Itabllizer circuit compriling e pass tranl lalor end zener diode willbe sullicien!. The operating current dreln !low ing through the Gunn elemenl emounll to emallimum 01 50[) rnA et en RF power 01 50 mW. II one ia uti l l ied wilh en output power 015mW which is sulficient for communicetionl even over greeter dlltanc.., the current drainwi ll only be epprOllimalely 200 rnA. A sulleble Itabilizer circuit i, given In Figur. 14

T1Ie 140O C ~ M ' 001 -u ~ !), '. ~h' " . Cl C" ltlO}I- " -,"0 I IhI

""

The fact that small voltage variallons at Ihe Gunn diode cause Irequency variations meansthat it I, possible to use this l or Irequency modulaUon. The 'upply voltage la thus led via thesecondary winding 01 a transformer and lhe primary s i del l connecled 10 the moduletor .A Irequency deviation 01 more then 50 kHz will be obteined with e modulating voltage ofap prOlllmelely 0.2 V.A loudspeaker Iranslormer from en old trenalSlor redio can be used es modulellng tranalormer. The Iowlmpedence winding (loUdspeaker connection) i , connected to Ihe modulator.The op erating vorlage of the oscUlator I I led vie Ihe high-impedance winding. Thl, cirCUitallows a clean end clear modulellon, whose quality i l conllderably belle r than when using enope rati onal ampillier, Flgur. 17 ahows the circ uit 01 a l ultable modulator which II able 10comple tely drive even the higher-powered Gunn elemenlS. The new Integra ted ampUfierTOA 1037 e!lows an r e m e almple ceee trucucn: normal dynamic microphones can beuN dIt Is neCeu.sry for Ihe modulating cable to be grounded with respect to RF vollages in ordarto evold parasitic oscil lation. In order to enlure thaI the bypaSI capaci tor does not 'hort outthe hlghe, moduleting l requencies, III tepacuance Ihould not be greete, than 4.7 pF. Thiscapaci to r should be mounted as naar to Ihe oacltlalor connection aa possible.

- t72 - , \ VHF COMMUNICATIONS 3/1977

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_ _ _ _ _ _ u _

At. 1': 'CobcN.d DC0 MT 00 1 f)g. 11; 1'C.fMNo", DC0 MT001

OC Itl M10 02 Hut sink

5

3pf.

l OA lOll (I ~ 6 I[ 1 47p [6

Pt 6c I I oPtO ~ 1 7 [3 [4 C7 470 J,J Louds

~4n7 68n treesRl :l-' [ I RI [5 R3 R4

lDDkC 47p 56 In 100 5n.6PI

1 . l

A VHF COMMUNICATIONS 31lln 173

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4. PREPARATIONSBefore Iwltching on, it il yery Imp o rtant to ... whether tM Gunn diOde I, co rreclty pllcedInto th e holder, l inc e the wron g polarity will d" t roy the Ileml nt, The ope rl ting Yolt .g . i,' irsll y . dJusted to thl l o w nt Yltue ( lpproJC , e to 7 V). Sinc e the current d rl ln YllUH 0' y . rlOUIGunn diOdei lIuetuete grN tly. no orlentatoon y.lue u n be glYen ' Ot the curren t d rlln. How....-r. It shOuld no t be more thin 100mA In th e cue 0' 5 mW etlmente. II the YOltao' il thencarelully i n c ,.. . . ." the cu rrent will li", tly Ii.., but will then till on I f ' C r N l l n g th e yolllQl 174 A VHF COMMUNICATIONS J J 1 ! i ~ n

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further. The required operating point il to be round jua. belore ma..imum cutrent. A l implediode probe can be uMd to check to see whether oscillation takel place. Thi l diooe pro be ilrequired later .. ml..er. The microwave diode (lUc h aa type t N 23 ) la placed In the center 01the waveguide. On. pole II connected vi bypua capaci to' to m.ter. Flgur.a 20 .nd 21give detai l l 01SUch I probe thai can be very uMtul lor adJu ltmenl 0 1Gunn olc ill l tO".

T flon d,se

'--- - " "--- 42".

,

So"~ ; : ; ; ; ; : : r ~ sold.t '4

'"...

!'lal.,.,o.( bfc.n 63

- ~ -

14 diode mount

,JE., ,1'18.0 .),..J ,

Bross 6l -$- + T,llonPart 1 PartZ~ VHF COMMUNICATIONS 3/ 1917 175

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The maS! ....Itabilt type 1N2 3 II . . , .lIabie Vlrtu.lly rterywhet1l The . .ner foUow ;ng thedeaign.lion indlCIIt. tNt noi.. h g u ~ .nd the further lhe letter II in IN alphabet. the ~ ,will be the no-. 'IOU,.. S i ~ tM ....lun 01 the diOOel .pl'MCl c o n ~ It illrecommended that ......,..1 dIOdes be purehaMd In oreter 10 Mlt th e arM ha v.,'", In. bestChar. ctaristlcs : highest lront-to-back r.l lO. highest dloda e u ~ l . low.t noi.. AlthOugh t ~look a llka. the diOdes type 1 N 21 or 1 N 4UI .,. not ....'t.b. . Sinea they _ 'a constructed 10'd ,t1.,.nl frequenctes.u . w....egu. . CompoMnlaProfessional wawgulde components . , . onen to be found on the surplus m.rket, Of cou rse.bra.. tubIng with a rectangul.r CroM-MC tion can also be uNd , and oll,n 'ept'HenlS lhemost Ine. pensive solution , How.....r, tha dimensions . , . oMen d,fI.,ent Ih.n th. t 01 thes tanda rdized profession.1 w....egu ides making combinations dlfllcult.REFERENCES(1) SIEMENSAG: Linnr, SCh.llungen. O.t. Book 1975m(2) 0" O. E..ans : Lacture.t tha VHFUHFConven tion In Munich

To be continued .

MEMORY KEYERMK 1024Mamory kay., ...,lIh lou, Ind , pendent memoria. 01 251 Bit,ach. Can be eomtMned tooblaln a memory ~ h 01_ 102. BIL

Pu . " b u110 nl 1o, M lacl lO" 01 .....mory Ind ttlrt . r-..t I ~ ttOP Squ.." ..... ,1'IOd 0 ' " " , ,-Iuloml!,e BUIII ,n Ose ,I'- ,O' W,Itl ...I ' l ible I,aquenty ,nel VOlu ..... Bulll ,n 1 P H II Wi ll I I ~ " 10 ' , , p a l ~ " BUIII,n l" nl ll lOI 0 ' ~ I I Y Iwlle",ng M.. IWlletl,ng powl l r"n, . .IO, mOClI ISOV I 2 " R mod i 700 V l OS A Opa'IMg VOlta;. 220240 VAC, 0' e . 14 V bln l ry O,m ln"on, 14()mm &0mm . 18Smm Wl lg hl 23 . "

178 , \ VHF COMMUNICATIONS 3'1977

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L INEAR CAPACITANCE METERby R. A.u la" DC I PC

This capaci tance meier II very simple to conslrUCI a nd's lu ltable lor measuring capacllinc in the range between approlllml 'ely 2 pF and 1",F with an accuracy 01 :t 3 , . . even capacltors with . certain polarity can be measured. The scale 01 the meter need nO be changed if moving coli mele, wilh lu ll-ICl le deflect ion 01100 ~ or t rn.... 's uNd . ,inca the capaCllanceacal . i' Un r. The wir ing I I kept to min imum by mounllng the range SWIlch directly on thePC-board .

' 1'1. 1:Ttl. lnla"rated timer CIrculiHE 555. with a n - m a l cIrcuitl or u. . .. M_ ftop

,.-I , . . ....I ,",,.. ,"1' I ~ II i,I ,_,, lI CI

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u DC 6Fe

u,,"1-_H-_ + L _ ...J...J......_Fig. 2: OUlput pul... 011M Yonoflop

II equat ion (1) I, placed lntc equahcn (2j , Ihe lollowlng will be obtained :1.1 11R I C .UOUrnean I ,

This means thf,t Ihe mean vi lua 01 the voltage result ing 'tom Ih. pulse chain 'I directlyproportional 10 I"" ca pacItance to be me.sured . The mean voltage ia now Ind icated on amoving coli meter that Is able 10Integrate the pulse, . In order 10 achieve this , It la n. cal leryfor the frequency of the trigger oscilla tor 10 be sultiei.olly high: In our case 500Hz.

DC6FC 002 Bereich/Range ,f , SOO Hz S s , a ~ PI3)1 ~Rl ee R2 RS , 5Dk M 10' ,. 12 V

T1 2 NE co LQmA2N 2646 T2 I C35 555 PI6 ,., I Rl2M- I " '"Cx "t On R' _ C2 PIS PIt.ell,. R3 100 100 R6 M R13P" e ePI P2 P3 " ' ) "" "I2 Pt1

180 A VHF COMMUNICATIONS 3/1977

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OperaUng voltage:Operating cu rrent:Measuring ranges(lull-Ic ale):

Flgur. 3 , hows lhe Cl rCuil dllgram 01 Ihe complele clpacllance m. ler . A unlJunCllon Irl nsisior (T 1) i . used as 0sc:1II110r, which produ ces nlrrow pu t... wilh I lrequency of IpprOIlImllely 500 Hz. The frequency Is d.pendenl on lhe RC-Unk R 1 I C 1. Trln . l. tor T 2 cony.rt.Ihe pUIN S to Irigger pul.... ,u ltlble lor the integrlled Ilm. r circuli NE 555. The RClinkcalculated according 10 aq uallon (1) con.i.l . 01 the range re. lslor. R 7 to R 11 Ind Ihe ca pacllance 10 be m.asured. which Is connec led betw&en connections pt 5 and PI 6. The m. l .rhaying 8 lullacale deflection oI l mA Inlagrelealhe output pulae, . Trimmer potentiomeler P 1Is proYlded lor aUgnment 01 luU-acl l. eeuecuon . Since Ihe cirCUit PONeIl.S an Inlrln.lccapac itance of approximately 25 pF, It Ie necessary lor the zero polnl 10 be compenUled In11'1 . two lowest ranges 0 1 100 pF and 1 nF. This il mlde el.clricelly uling resillo ra R 12, P 2I nd P 3. Potanticmel.r P -4 II I'SO prCl'l ided which IIlOWl the connection lead capacltancel 01disc and rotary cepac itora to be compensated lor In Ihe moat ..nlltlv. measuring range. Thilpo lenUom.ler II accesa ible elliernally.As can be seen In eq uation 2a, the operating vollage Uo I nd the Irlgg. r lreQu. ncy. or Itspe riod duration tz have an eu ect on the Indication. For thl, r. ason II Is nee....ry lo r mem 10be atable .

2. SPECIFICATIONS12 V. stabili zedapprox. 40 mA1. 100 pF2. 1 nF3, 10 nF4. 100 nF5. 1 I/oF

Smallest capaci tance vllua: ap prox, 2 pF

3. CONSTRUCTIONThe circuit shown In Flgur. 3 I. accommodaled on I PC-beard having the dimen.lonl 55 mmII 70 mm. Flgu,. -4 shows this I lngle-coaled board Ind the componenlS locaiioni . The boardhas been deslgnlled DC6 Fe o o ~ Th. aulhor 's prototype Is accommodaled in I TEKO bOiltooether wilh a amall power l upply. Figure 5 $hows I drlWlng of the lron t pInel. The largerthe meter. the mere accur lte will be the m. as ured valu...3.1. COmpoMnl D.tsllsT 1:T 2:11:R 7 -R l1 :C 1:C2. C3 :

2 N 2646or TIS.,Be 237 or olher NPNAF transi. torNE555 V(SlgneUca)ca rbon reslltOrs, 1/6 W, 2 %-4 .7 nF plast ic loll cepecllor, spacing 7.5 mmCeramic diSC capacitora

~ VHF COMMUNICATIONS 3f1977 - t81

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P 1;P2, P3 ;P4 :Meier:SWitch :Cliblnel:

10 kO (or 100 kO lor 100 lAAmeterl trimmer potentIOmeter , spacing 10/5 mm100 Q tnmmer potentIOmeter, &paCing 10/5 mm5 kQ potentIOmeter100 IAA Of' 1 mAo40 mm ... 40 mm Of 60 mm ... eo mm2 ... 6 change-over SWitch, 6 mm aha"TEKO PI P3

!.

OC6FC00' 0 G . ., G0 "~ : ~ . ~ ~ , ~ ~ ~

p ~..~ ~ 0e-, B-*u ,G )~ 0- o ~ ~Ill . "~ ( ~ ~ A~ Tl -=;;;l (OJ-fOil ~ "=- "........ -mJ;;

.. NuIlPI,,nkt ..lO Op Z.ro

0 '" C)o.1----" ' DOn'.A0 CX@ e

DC6FC 00' (.J.. ..

1112 , \ VHF COMMUNICATIONS 3/ 1977

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4. ALIGNMENTThe o,clliator I, Ilrstly a l i g n ~ to 500 Hz :t: 75 HZ by 'll.changing r ', I,IO' R 1. "Itar thi, . a'tyrollall. capacitor 01 10nF :t: 2.5 '" (Siaman.jlhOuld be connected to ttla input and cc tentiometer P 1 aligned '0' lull ,cala In maaluring ranga 3,This Is lollowed by adju,tlng tha z.ro points In tha two lowar rang., With trimmer rei litor,P 3 and P 2. P 4 'hould be In a cantral polltlon. The alignment I. than complat a.5. REFERENCES(1) Signatl cs data and applicati on sheet lor timer S55(2) C. Hall: Dlrect.reading capacitance matarHam RadiO Magazine, Vol. 8 (1975), Edition 4. Page ' 32 35

MINIATURE VHFUHF RECEIVERSand Scanners for Both Professionaland Amateur Applications

UKW 2UHF 1

UKW 12 AliiMOClul' I,on mOCloI '"'........'on.Accl l lO' '',UKW12 FillMOClul. t,on moot '"urlln"on.~ r , "UKW 2Modul. hon _ '".......,lIon.AcCl l lO""FI I lu. . .UKW.MOClul." on moOt '"'........'on."'CCftlO ,,"UHF IMOClul. hon mOCloI '",!'nInllon.AcC_ ' , "F " lu ' "

12 c ~ . " " e 1 ","'I.lu...'. . . ."d 'ee. '... ." ; t 101 ' 38 MHI" 2 ...... , 68 ", ... . )3"''''AnI." ". " '0"0"' , ball."Y c""II"12 c ~ . " " """I. ..... VHF _Fill 'e e......

u e n c . ., , ; t 70811 MHI , ~ toll'll" 2 "' .68 ...... . 33 ......"" I " ohone. ba t!..., cl'Ie'll"2 c ~ . " 1mlftlelu" VHFflll .ee . . . . . .f .-o . , .nq 7Q8II to1HI U Q- l 70MHI120"''' ' .60 22 .......An.. ..n. , " rpr,on.e , !>lItr .., e""II"P " ' b 01 '" II,lIlnll ","0-10 . .. 111 ', .. Clil el l . "" .1 YHFFM .U""....c.I . . .F,eque"cy . .noe 70811tol l'll . ' .0. ,70 t,!HI1'2 " ..."' .32...'"Ani , I I rp/1Or>. , l"n . "Y c""III '1cr UH' _''''' ...1_1. . . . ,ee" ",' .-o cy ' :150 - $12MHZ120"' 6(1 22 ......An ,pr.o.ne. !>lItt.'Y e""l l""'110 'Iall.. I I _-C ........I .ee. . . . 'PoM'b,I,1y0 ' ,. ..tall,fIO_ ' 10. . . 1111 ' ' ' e.1I

" h . , 01 lhl ...,n" lu " 'ee" . . . . 0.5 ee 1 I 2008 S,NO'ltfibuto, enqU"'" welcomeo:l

U K W T E C H N I K Hans Oohlus oHG0 8523 BAIERSOORF . JahnstraBe 14Telephone (09133) 855,856 ' Telex: 629887Bank .ceoun. . : Po, l ten.c:k Numbotrg 30 . $t1 . llSl!I

eomm.rzo."k ( rla"1il." 8 2 0 - 1 1 ~ 183

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THE AFC LOOPA Simple and Cheap Method of ObtainingStable VHF Frequencies

by Q. HoffschUdt, DL I FX

Nowadayl , the requ ited loctIl oscillator gn al i l ulua lly u. .ng Ir equency synthesiS or .n PLL-oICIUalor . A PLL-oscillalor ia normally prelemtd dua 10 lha bellaf speclra l purity 01 lheoutput l ignaLSuch an oscillator usually opera'.. , Ih. reqUired output lrequancy (VCO, anduses. phase or frequency ccntror lOOp. In tne case 01 phase comparalor, me res,dual erroris only a phase error. and Ihe relallvl accuracy of Ihe output frequency corresponds 10 Ihatof the telarred lrequency, il Irequency (llvi(lltr. ar' uud in lhe control l yllem. In Ihe casl 01a frequen cy comparator , the residual arror will always be freQuency arror. For th l l raason,tne trequencv control lOOP is ma inly only used in automal lC frequency conuct sySlema. suchas ollen found in VHF/FM broadcast receiver. where an lutremely high IreQuency accuracy isnot requ ired, II the control loop is correct ly designad Ind when modern lnl8graled CirCUitsare used , the residual freQuency error can be so small lhal it is more than sulhcient loramateur rad io applications . There are also a number 01 interesting pouib il illes lhal are notpoSSIble when using a phase locked loop: voltage-Itnear tumng (LMO), generation 01 any Irequency spaCing, as well as conatant IreQuency ahll! lor repeater operl l ion . Such a Irequencycontrol lo op is to be discussed and exp lained in Ihls art icle,

OLI U."I > H W ~ H@:j,."..Fill . t : Block dlag,.m 01 the Irltqu8lloCr _ lrol loop.Th, ~ t l o m e .. ",Nd lor Hn8.r-.oIl8118 tIlnl",. 8 .01l8ve dl.ld8rco"nec1ecllo UREF . . "'Md lor lIeneritlOn 01 8 tertlln Ireq"'l lloCr 8p8elng,

1. PRINCIPLE OF T1iE FREQUENCY CONTROL LOOP

The con, ldered l requency control loop Ihould cover a range of approximately 500 kHz in Ihe2 m band . A block diagram Is given in F1gur. "Jt will be teen that it Is the circuit Or a PLL-oscillator. The lrequency of the oscil lator (VCO) ilmiXed With a crystal-ccotrolled frequency. and the r..ulltng output frequency led 10 a discriminator. This converts lhe dif ference frequency 10 a voltage that iafrequency-proportlona l.This la then ted and filtered In a low-paas filler which la not ahown In the diagram. Thi l DCvoltage is leel 10 a tomp.lrltor Ind compared 10 In external DC-voltaQ8, The outpu t voltageof the comparator Is used 10 lune lhe oscillator 10 the nominal Irequency.Thl, means that the outpulfrequency la not only locked to a cryalel-eontrolled frequency, butalso 10 a oc.VOltlge that can be vlried within a relatively wide range. The frequency liabilityand accuracy that can be obtained are mainly dependent on the charlc teril l ic. 01 Ihe dll criminator uled a, frequency-volt age converter,

164 - , A. VHF COMMUNICATIONS 3/1977

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2. ntE FREQUENCY DISCRIMINATORA monc-stebre multivibrator (Monollop) is suitable as discrimln8l0r. An example 01 lh ls Is theIntegrated TIL-elrcult type SN 74121. The operation of this lC can be explained With the aidof the pu lse diagram given In Flgur . 2.

r - J r - J ~J L........J L ..,,, ,'....--." " ' = = ~ ---,. . . .. . .w '.."" ,' . Fig . 2:Pulle dleg ram of litefrequency dltc rlmlnalo r

II a pulse Is led to the Input. a pulse having a constant length will be provided by the output.The length 01the pulse Is dependent on the AClink connected externally.

u U. , I, (1)I, T I,I 1 (2)I, T I,U u, x I x I, (3)

The mean value U ot the output VOltage Is direc tly proportional to the input Irequency. thusthe operation 15 strictly linear, If the relerence DC-vollage at the comparator is varied Unearly,or in steps. the frequency 01the veo wlll lollow this Unearly, or In steps,

3. FREQUENCY SHIFTThe poss ibility of providing a consiant Irequency shil l 01, lor tnetence. 600 kHz lor repealerope ration. Is shown In Flgur. 3. In this esse. the reference frequency Is placed between thetwo required bands. A control loop that has been designed for the lower band (repeaterInput) can also be made stable lor the upper band (repealer outpul). Since the output frequency lies abo.... Ihe cryslal frequency. it Is neceSlary for 8 phase reversal 10 be carried outat some position in the control loop. This can be carried out most favorably at the discrim inato r by switChing between output a and output t5 (Inverted outpul). The conditio ns areshown In Flgu, . 4,

r-'! r 2..:1. OLi n._ -1-I11III__ ,."...... ....-.......... ........'".Fig. 3:Po..lblllty 01 oblaln lnga oonatan l l, eq uenqo I hlf'!(e.g. &00kHI)

~ VHF COMMUNICATIONS 3/ 1977

..._1I.'",".. ...,., "

FIg. 4:f11l le llo n,hlp , at Ihe pul..dlacrlmlnl!J.0r on , . llChlngIrom a toO 185 -

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4.3.1. OffaetVoltlige end Curren'It la only Ihe temperature dependence 01 theH p.8ramete,. that Is 01 Interest lo r the l requencyItabillty, It Is assumed that the temper,ture dependence II 10 IAv rc . Thil value II usually notexceeded aven when ullng Inexpenalva comp.arltora (operallona l ampUier, ) . II 5 V DCvoltage I, requ ired , t the comparator Input to obtain I tun ing ranga 01 SOO kHz. a vollagevariali on 01 10 IAV will eluse a frequency varlaUon 01 1 Hz. corr l lpondlng to a relahve IreQuency verlatlon 0' 0.067 x 10'rc.The temperature dependance caused by the OflHt current I, 01the , arne order.

6. Ue I 6. Us I, In the oraer 01 50 IJ.VN ; th l , mean, : an operating voltage variation 01 1 V willha". the same effect I I 50 IAV input voltage variation . II it is once again a l lumed that 5 V arerequired 'or !he tuning range 01 SOO kHz. the OIpendence 01 Ihe opef l ting voltaga on thecomparator is calculatad to be 0.33 x to'tv.4.4. Effec' 0' the Releflnee VollageI' the d iscriminator and relerence ara fed 'rom the ,a rne voltaga lOurce. no additional arror,will occur In addition to tha above. since tha variation 01 the ralerenca vottage will have theume magnitude as It'll variation 01 the output vonage 0' tha discrlmlnl tor. This malna thl tno dilleranee vollage Is axhibited at the complralor Input .

4.5. Frequency Error of the Control Loop - Residu al ErrorAI was mentioned in the IntrOduct ion. a IreQuency error wilt alwl y' be praHnl as r..idu l lcontrol arror in the CU I 01 I IrlQuency control loop ,The frequency control loop can be assumed to be an amplifier with leedback hnk as shown InFigure 5, As in the elM of an amplif ier the follow ing relat ionship exists:

fb 11 + l l xGF" , OLt Fl

FIt. 5: Thl fr....nc' tonlrolloop. . Impll liar wlltllalClbaekwhere Ib leedback l i etorwnere a fractiOn 01 the output voltage used lor leedback;In our ceH the ratio 01 the discriminator output vonsge 10 the vareclor diode vottagerequired lor a del ined tun ing 01 the oscUiator.o Oaln 01!he comparator wlthoullHdback (OPln loop)," VHF COMMUNICATIONS 31t9n 187 .

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NOTES AND MODIF ICAT IONS1. NEUTRALISATION OF THE 500 MHz PRESCAUA DJ ePI 005A tendency to oscillation was observed with some models 01 the 500 MHz prescale, OJ 6 PI005. II Is observed when the Input connector is unlermlnated as lUckerlng counter read-cutIn the order 01250 MHz, and is even visible when the supply voltage of the OM 335 has beenswitched off. This ettect was firsUy thought 10 be caused by low-quality SP8515. however, Itis caused by especially good type s. II will be seen In the dala sheet that the maxtmum eenetl ivity of Ihe SP 8515 is in tha order 01 250MHz. For this reason. the manul. cturer. (Plessey)state thaI a tendency 10oscilla!lon In Ihia frequency range is poll$ibla.Any tendency to oscillat ion can be neut ralized simply by placing a resistor between Ihe inputof the SP 8515 (pin 10) arid ground. The reslslance value musl be found eKperimenla lly foreach individual Ie. Aller swil ch ing oi l Ihe supply vollag e 01 24 V, one commences wil h avetce 01 100 kO and me value is reduced until a Sable 000 read-oul is available on Ihecounter . Even w ilh Ihe lowes t possible values In the order 01 15 kO. the sensitivity 01 theprescaler will hardly be affected: lo r instance trom 2 mV 10 3 mv al 400 MHz.In add ition to these measures, the lollowing should also be observed:The outer conductor 01 Ihe coaKlal cable between the Input eccket and board OJ 6 PI 005should be grounded at both ends .The output 01 the module shoul d not be connected to a high impedance Input . but di rectlyco nnected to Ihe counting gate (usuelly a 74S00).Since Ihis tendency to oscillation was not observed with any SP 8515 types used in the prototypes and belore publication of Ihe art icle, no room Is available on the board lor th isdamping reslslor . However, il can easily be mounted on ei ther side 01 the board betweenpin 10 and ground.Another unwanted effect Is that a harmonic 01 low trequencv signals wil l be Indicated al inputvo ltages over approximately 1 V. This overload enect can be avoided by using an eKlensivecontrol ci rcuit using PIN diodes. In order to avoid this. it should be nOled thai the preecalershould be driven with the lowes l possible voltage, or via an attenua tor,

2. A TRANSCEIVER FOR THE 10 QHz BAND

In the case 01 the Gunn diodes type 008 -68 A suppli ed by the publishers. Ihe anode Isconnected to the heat sink (Ilange). This side must be connected to the minus pole 01 Ihepower supply. II the output voltage h om the modulator Is negat ive. a galvan ic coupling 10 th isGunn -elemen t will be possible. II not , a tran sformer mUll be used as described by DC 0 MT.

3. DC 8 NR LINEAR TRANSVERTER 144MHz - 12M MHzAn output power 01maximum 1 W can be oblained by tuning Ihe coupling links in Ihe linearampillier to lhe reQuired Irequen cy. This can be obtained by providing amall copper loil strips01approxlmalely 5 mm x 10mm to the hot end 01 the coupl ing link a, which are Ihen luned byaltering the capacitance of Ihese strips to the screen ing wall s. Inductance L 3 should betuned to 1152 MHz, L 5 and L 7 to 1296MHz.. \ VHF COMMUNICATIONS 3/ 1971 - 189

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MA T ERIAL PRIC E L I ST OF EQUIPMENTdescribed In Edition 3/1977 01 VHFCOMMUNICATIONS

OJ 0 FW 001PCboardSemiconductorsMlnik.illMlniki l2

Crystal f illerCrystalSel 01crystalsComplet e k it

RECEIVEROJ 0 FWOO1OJ0 FW OOtOJ 0 FWOO1OJ 0 FWOO1

OJ 0 FWOOIHCt8/UHC1B/UOJ 0 FWOOl

(double coated. lhru-con lacl sj(10 tran Sistors, 1 IC, 11 dIodes)(7 coUse's, 21errill chokel , 5 Irimmer cap .)(50 ceramic bypass ceps., 2tlnlalum caps "18 ceramic caps., 53 r .alstor. , 1 tr immerpolenhomeler )(10.7 MHz)Channels R 69 72, R 72 75. R 75 78.R 78 81 , R81 84 , R8.4 87, cry" l ls eachAny fou r 01above crystallwith above parta (Incl. t 01crystala)

Ed. 3/1177OM 32.OM 79.OM 52.50

OM 38.OM 30.-OM 16.OM 60.-OM 21$.-

OM 77 . OM 11 . -

Ed. 311177OM 6,50OM 9,50

(wI thout plan )(without plan )(1 TDA 1037. 1 Gunn d iOde oeG 6844 A.1 diode 1N 23 E)

DC 0 MT 001/2 wi th above parta

OCOMTOOlDCOMTOO2DCOMT

Kit

DC 0 MY 0011002 POWER SUPPLY and MODULATOR lor GunnOaclllator.PCboardPCboardSemiconductors

OJ 1 ZB 002Kit

70 em BANDPASS FILTEROJ 1 ZB 002 (1 silver-pteted case ,Ilver-plaled solderlags. 2 trimmers, 2 BNC connectors . Silver

plated copper wire)

Ed. 311177

OM 41.-

DC 8 Fe 002PCboardSemiconductorsKit

CAPACITANCE METERDC 6 FC 002 (wlt l'1 printed plan)DC 6 FC 002 (1 IC, 2 Iransistors)DC 1 FC 002 with abo.,.. Plrtl

Ed. 311177OM 9OM 10,OM 11.-

Verlag UKW-BERICHTE, H. Dohlus oHGJahnstraBe 14 - 0-8523 BAIERSOORFWe. t-Germany Telephone (0 9191) 91 57 or (0 9133) 855, 856

Blnk I ccounl1; : POi tacl'1eck NOmberg 30455--858 Commerzblnk Erllng.n 820-11S4Stadtaplrkuae Erlang.n 54)1 . 51 Aailf. i.enb,ink Ertangen 410.0&0

- 190 - A VHF COMMUNICATIONS 3/1977

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COMNI R-10101120 Channel VHF Alrband Receiver with SynthesizerFEATURES : 1120 channels tOt NAVICOM wl lh 25 kHz spacing Eu et frequency select ion 01MHz and kHz Electronic dig ital r dOlJt Sm.U and handy Extremely M nslli .... doub le superhe t For AC and battery oper, tion (Connection cables provided)SPECIFICATIONS :Frequency range :Rece ive channell;Channe l spacing :MOdulat ion mode:Sensiliv ity :Bandw idth :Intermediate frequencies:Osclll8lo ,.. :Spu rious and Image re jection :Control Ume (AGe ) :Built -In . ,htcl lve nolae blanker :Input connector:Temperature range:Audio output:Built in loudspeaker:Operat ing ... o l t l i ~DC-cu rrenl dre ln:Dimensions :Weight :Supplied accessori.,:

. \ VHF COMMUNICATIONS 3/ 1977

108.000 1 35.975 MHz112025 kHzAM (A 3)< O.SIIV 1 20 dB (S -+ N)/N15 kHz10.695 MHz / 455 kHzt et: PPL-aynlh lz. r, 2nd : crystalBelter then - 60 dB0.1- 0.5 .e .pec ial ly designed lor mobile use50 C, 80 239- 2O"C to + 6O"C> 1.5 W I < 5 '" distortion8 C. approx. 60 mm dia.13.8 V % 15 '" I 220 VAC 50 Hz0.8 A160 x 56x 250 mmapprox, 3 kgPower line cable , ballery cable ,lelescope anlenna, mobile mount

191

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NEW ANTENNA ROTATINGSYSTEMS from UKW-TECHNIK

Anlenna rotating system . 1 described In 1/19n ofVHF COMMUNICATIONS

. , .. - -!--1I

1'101.10 . UIlW MIOl l_AC VOlTage 220 V I 50 HIVott19- 10 tOtIIlOI"

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