iivc. - to-way · introduction in this booklet, we preserll '10 gernlaniurll diode...

$: IIVC. - To-Way · INTRODUCTION In this booklet, we preserll '10 gernlaniurll diode applications, hied ant1 1,ro\.cn, which tlitl not appear ill the scveral crystal l,oolile~s publishetl$

CRYSTAL DIODE

Circuit Kinks

MORE NEW USES

FOR G E R M A N I U M

DIODES

Sylvon ia Electric Products lnc., Semiconductor D iv . , 100 Sy lvan Rd., W o b u r n , M a s s .

INTRODUCTION

I n this booklet, we preserll '10 gernlaniurll diode applications, hied ant1 1,ro\.cn, which t l i t l not appear ill the scveral crystal l,oolile~s publishetl pre- viously by our Corrioany. \\It believe tlie engineer, service technician, transtnillirlg rarlio arrlateur, and liobbyist all will find items of inlcrcst ill this new collection of circuits ant1 dala. I t is believed further that the ilenls conlainetl in tllis Looklet will provoke furllier t l iot~gli~ and cxperinlerita~ion on the part of readers-activi~~ wliich will leatl to tlevelopment of even more applica~ions of the already prolific germanium tliotlt.

In recenl years, the crystal ~ o l t m e ~ e r and mis- cellaneous crystal meters have altained an itlenlity of their own. For this reasori, a separate chaf,ter lias been devoletl to melers. Increasing acceplance of he gerrnaniurn tliode in TV reception likewise has occurrerl, arltl a tlescription of successful circuits in this category appear i r i Chapter 3.

This bookle~ is oKerecl w i h tlie earnest wish that i t will bring prac~ical idea5 L O radio-television technicians everywhere.

SYLVANIA 1ILEC:TRTC: PR0DUC:TS. IIVC.

TABLE OF C O N T E N T S

... lr~troductior~ 111

1,ist of Illustrations \ i i

CHAPTER I Crystal Meters and Meter Accessories 1

1.1 Linear Voltmeter for I j l l i l t - i~~ I r i s t r ~ ~ n ~ e ~ ~ t a t i o n . 1.2 Tube- Driven Linear C:rys~al \ ' o l ~ m e ~ e r . ~ . 1.3 IIigll-ltc=iatance Cryslal V o l l n ~ e ~ c r . 1.4 Sq~iare-La\$- D. C. V o l ~ ~ n e l e r . 1.5 Ballistic Ale~cr lo r Single T~ : I I I . -~~I ILs . 1.6 S i n ~ p l e A . i:. A I i l l i v o l ~ r ~ ~ c ~ e r . 1.7 'rra113- lorn~er-Cou~,let l ;\. I:. ~ I i l l ivo l tn~c tc r . 1.8 A u d i o - F r e q ~ ~ e r ~ c y Micro- vo l~er . 1.9 D. C. Aleler Compressor. 1.10 Pcak-lo-Peak 'I'elc\.iiior~ . Vollrneter I'rol~e. 1.1 1 Full-n'avc Current RIc~crs. 1.12 Sr~ . ie - - ( :o~~- r~ecled Diodes for Fliglr-\'oltaFe A . (:. Rle~ers .

CHAPTER II

2.1 I r r ~ ~ ~ r o v e t l l.o\v-ldc,vrl I,'rcquc~~c.!- h l u l ~ i l ~ l i c r . 2.2 1lsr111011ic .-\cce~~lualor lo r Excilers. 2.:; Sinil~le Cuei t~g Itecei\.cr. 2.-4 Al111)lifier I'roteclive Ilelay. 2.5 (:a~.rier-0l)ernletl l:ecci\.er ilI111i11g Sys- [ern. 2.6 Voice (RIodulalion) Con~rol let l I<el:iy. 2.7 l l o l ~ i t o r Ile- cci\.er for Eroadcas~ ' I ' ra~~. ;rni~trr 1.ocalior1. 2.8 ,431 Ilecei\.er Noise 1.irni1c.r.

CHAPTER Ill ?'I. nrlrl Radio Serrire 1)c.t-ires 1 0

ii.1 'I'\- A I I ~ ~ I I I I : ~ O r i e r ~ l a l i o ~ ~ hleter. :3.2 S e l l - C o ~ ~ ~ a i n e t l I.'icld S l r c ~ ~ ~ t h hletcr. :3.:; l ~ c n ~ o d u l a t o r Prolw for 7'1. Oscillo;col~e. i3.11 ' I ' I I I I ~ . ~ ~ (:r!.stal-'l'!.l)c: 5ig11al 'I'racer. :2.5 'I'ele\-i.io11 \'itleo I)c.~ccto~.. :5.6 IAI.'l\' Di:crinli~~ator. :3.7 FhI Dyrian~ic I J i n ~ i ~ e r . T\' (:as- cadc 5yr1c Clij)l~er. 3.9 ACC Peak Detector. il.10 T\ ' \'c~.tic:iI I'ulsc Se l~ara tor .

CHAPTER IV

-l,.l A r n I ) l i ~ ~ r d e hlodulalor. -1.2 Ilridged-T I'llase llotlulator. -1.3 Sl)ike Gel~cralor. -1.1 I'ulse (;c~lerator. d.,i Sa\vtootl~ Generator. 4.6 Gerrtianiunl Triode I'orver Sup1)1!,. 4.7 RIiniature Light- lntel~s- it)- hIeter. 4.8 I n d i c a l i ~ ~ z Audio I.'requel~cy hleter. 1.9 V o l ~ n ~ e - Selec~ive Circuit. -l..10 Gern~nniurn Diodes a3 CIII.\'C' S ~ r a i ~ h t e n e r s .

O n n l i n i o t u i e diode, w ide color bond designates cothode end of

diode

I n a l l Sylvanlo circuit dlogramr rhowing germanium diodes, the bar of the diode symbol rep re^

rents the cothode. On Syivonlo G e r n l a n u m Diode shown obove, the cothode end is ~ndicoted by a color bond ond the lobel

"CATH"

I-IST O F ILLUSTRATIONS

F r g t t ~ (. R'UIII~IC~I~ Title 1'11,qe

I:i211re 1.1. ~ r r i c ~ s - l y l , t ~ l.i~~csar \'01tn1c~tc~r for 1<uiIl-i11 l ~ ~ ~ l r ~ ~ r r ~ c * ~ ~ t : ~ l i o l ~ . . . 1

1" i~ure 1-2. S h u n ~ - ~ y [ ) c > I.ir~c.ar Vol1111c)tc:r for Iluill-ir~ Instr~~rnc,ntatior~ . 2 I 1 I ; ' ~ ~ l l - t ~ r i t l ~ t ~ Tut)c.-tlri\c.~t Yoltn11.1c.r for Scxnsitivc. A.I.'.

AIcasurt~ri1ot11s ....................... . . . . . . .................... .......... . )

1." I ~ L I T I . 1- 1. Hall-1)riti;c. Tul)~*-dri\,ctn Vol~mc%tc.r. for Sc~r~sitivc. -2.1.'. hleasurcrnc~nts )

1:igul-e 1-5. High-resis~a~lc,c Crys~:~l \Jol~rl!t.tc.~. ...... .. . . . . . . . . I I;igurc. 1-6. Srlr~arr-I,a\v U.(:. \'ol~mc:lc,r ............. ........ .. . . . . . . . . . . . . 5 1:igur.c. 1-7. Ballis~ic hlctcr lor Sir~glc Trar1sic:lts (i

Figure: 1-8. S c ~ r i c ~ s - t Y l ~ : .\.(:. Millivoltrnc~~(~r ............ . . . . . . . .. . . . . 7

I.'igurc 1-9. Tr.ar~sforruc.r-coul)led A.F. 3lilli\oltrnclc.r. ............... . . .. . . . . . . . . . . . . . 7 1:i;urc. 1-10, Audio-Irc,quc.r~cy hlic.ro\.ol~c.r 3

i r C 1 1 1 . 1l.C. 3Ic,~cr (:ornprc.ssor . . . . . . . ............... ..... ... 9 I'iyurc. 1-1 2. I'ctak-to-l)c%ak T(.I(.\.isio~~ 1.01 trn(t11.r I'rol~c. ... . . 0

I 1 1 I7ull-way(. Currc~11t hlctcr Circ~ril.: 11

i r 1-11. Scxric.s-diotlc Ar.r.nl~~c.r~~crlt for Hi;l~-\c,ltnpc. A,(: . \ ' o ~ I I I I ( ~ I I ~ ~ ~ . . 1 2 I.'i;urc. 2 11nl)rovccl Idow-lcxvc.l Frcqucr~c.!- \111l1i l~lic,r . . . . . . ... .. . 1 3 1:igurc 2-2. Rnrrnor~ic Ac~c:clnluator for E:\c.i~c.l..+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 I

T"igurc 2-3. Simt)lr Curing 12cc.civrr ..... . ............... . . . . . . . . . . ... . . 1 1 Figure 8-4. Amplific.1- I'rolcctivc Rrlay ....................... .......... .. ......................... . . 15 I;iji~~rc 2-5. Transrnit1c.r (Carr ier) Ol~c.rn~c~d Tlcc,c.i\.c.r R ~ I I I ~ I I F .S~SI( , I II . . 1 6

F i g ~ ~ r c 2-6. Voic,c: t l l o d u l a t i o ~ ~ ) (:otll rollcd Ilclay ...... ........ .. . . . . . . . . . . . . . 16 FiY~lrc 2-7. Moni~ol.ir~; 1lc:cc~ivc~r Tor 13roatl1,nsl Ts:~ns~nitlc.r I.oc.i~[iol~. . . 17 1:i;urc: 2-8. Iml)~llsc~ Noise 1,imitc.r ............. . . . .. . . ....................... .................... . . 18 1"igurc. 3-1. T.V. . \ r ~ ~ c n r ~ a Oric .r~tnt io~~ h11.11.r . . . . . . . . . . . . . . . .... . . . . . . 1 0

1:i;ul.c. :<-2. D r r n o c l ~ ~ l a ~ o r Pro111. lor 0sc~illoic~11~1c~ . . .... ... ..... .... 20 I.'i;ul.c> 3-:<. Tuncd Sig~lnl 'Trac.13r .............. ... . .. .. . . . 'L I I - 1 . Higl~-cfl;c.ic~~~c.~- \'idc>o I)c.~c.cto~ .. . . ...... . ... -- 9 9

i ~ r - 5 . T:.24.-T.V. T)isc,rirni~~:~~or . . . . . . . . . . . . . . . . . . . . . . 2:;

I 6 I:.RT. T ) ! - I I : I I ~ ~ ( . I,irnilt*r . . ........ . . . . .. .. . . . . . . . . . . 2:: I.'iz111.(, :3-7. 'I1.\.. (:IIS(.:I~C S ~ I I C . CIipl)cr ................. .... . . .... . . .. . . . . ... . 2 1. l, 'ig~~rc, :<-F;. A.(:,(:. l ' c ~ ~ i k U c ~ t c ~ , ~ o r ~11111 .4111~)lifi(~r for T.\'. . .... . ......... 2 I I - 9 . T.\:. \'c,rtic.:ll I'ulsc. Sc.l):~ra~o~. wit11 T . i ~ ~ ~ i l ( ~ r . - i r r \ c>rt(.r . . .. .. -. '> 5

I , ' ~ ~ I I ~ I > 4-1. ( ; ~ ~ I T I C I I I ~ I I ~ I I l)io(lc .411~l)lit11tl(~ >locI111:11or .. . 2( I I 2 I1rid;c~tl-'l' (;c>rn~:~r~iurn I'l~asc. 4lod~rl:1tor ....... 27 I.'ip~~r.c* 4 3 . Spikc (;c.~~c.rn~ol. . . . 28 I"i;urc. 4-1,. I'~11sc: Cc,~~c.rntor . . . . . . . . . . . . . . . . . . . . . .

tl ,. b LO

Fip,u~.c, -1,-5. S a w ~ o o t l ~ (;c.r~c,ra~or . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 9 I:ig~~rc. ~ l - 6 . ( ; c , r ~ ~ ~ n r ~ i u r l ~ Triotlr Po\vc.r SII[I~)~! . .. . . . . . . . . . . ... 2 9

FiX~xc. 1.-7. h l i ~ ~ i a t u r c I > i g l ~ t - i r ~ t r ~ ~ s i t y R ~ I C I . 30 I.'igurc, 1-8. Ir~dic.alin; Audio Frc:rlue~~cy hIc*ter ................................. .... . :< 1 i t I . C a l i h r a t i o ~ ~ Data lor thr .4utlio Frcquc~lcy J l r ~ r r . . . . . :3 1

7. . I.'irure 4 1 0 . VoltaKc~-sc~lrc~tivr ( . ~ r c u ~ t . . ........... ................ . . . ... . . . . . . . . :3 2

CHAPTER I

CRYSTAL METERS A N D METER ACCESSORIES

1.1 LINEAR VOLTMETER FOR BUILT-IN INSTRUMENTATION

0-IOV A-C SIGNAL

R M S INPUT -----t-- 1 c:;;;;;y&-

2 0 , O O O n WIREWOUND POTENTIOMETER

Figure 1 - 1 . Series-type l i nea r Vol tmeter f o r Built- in Instrumentation.

A small, wide-frequency voltmeter is useful on the panel of another instrument, such as a radio-lrequency or audio-frequency oscillator, for continuous monitoring of signal output. A built-in meter of this type eliminates necessity for an external voltmeter.

The simple series-diode crystal volt- than 10, the meter will riot be linear, meter circuit of Figure 1-1 is suitable therefore the builder must not aim for for s u c l ~ built-in instrumentation. The low full-scale deflections rinless he is 0-1 d. c. milliammeter indicates 0-10 willing to draw a special scale for the volts r. m. s. directly. This voltage meter. I n r. f . aignal generators and in range is satisfactory for most audio 0s- audio oscillators, the voltmeter also cillator applications. If the output cir- may be connected to the input termin- cuit of the oscillator is reasonably lo\\ als of the output attenuator in the in- impedance, response of the voltmeter strument. This will permit standardiza- circuit will be perfectly linear down to tion of the signal to a prescribed value 0.1 volt (1/100 of full-scale dellection at the attenuator input. of the milliammeter). The d. c. return necessary for proper

The voltmeter input leads may he operation of the crystal diode must he connected directly across the oscillator completed by the output circuit of the output terminals when the o u ~ p u t volt- instrument to which the voltmeter is at- age will not exceed a maximum of 10 tached. Ordinarily this return will be volts r. m. s. For higher output \.slues. obtained through the secondary wind- the resistance of the calibration con- ing of the output transformer. No d. c. trol potentiometer may he increased as component must he present in the in- required. At lower full-scale voltages strument output, otherwise the meter

CALIBRATION

2 0 , 0 0 0 n WIREWOUND POTENTIOMETER

Figure 1-2. Shunt-type linear Voltmeter for Built-in Instrumentation

will be deflected erroneously and the diode a r ~ d meter may be damaged.

If d . c, is present in the instrument o ~ ~ t l ) u t , o r i f rlo d . c. return ~ a t h for the diode is provided 11y the instrument output circuit, the shun1 vultmeter circuit shown i r ~ Figure 1-2 nlrlst he used. While this ci.rcuit is romervhnt less de- sirahle, from a loading standpoint. than the one given in Figure 1-1. itr cali1)ration is the same as thc former circuit.

1.2 TUBE-DRIVEN LINEAR CRYSTAL VOLTMETERS

S e ~ ~ s i t i v e a . c. v o l ~ n ~ e t e r s coml)ir~e a h i g h - g a i ~ ~ , \vide-l)arrd signal amplifier with a rectifier-type rrleter indicator circuit. S u c l ~ meters are widely used i l l

lal)oratories for the measurement of audio signal le\,els tlowr~ to rnillivolt ranges. The e x l ) e r i m e ~ ~ ~ e r may con- htruct a s iml~ le , s c ~ ~ s i t i v e a . f. voltmeter of t l ~ i s type by corlnecting a h i g h - g a i ~ ~ audio a~lrplilicr alleat1 o l a suitable lirlrar crystal voltr~leter. 1,inearity within the an~pl i f ier rrray I)? improved by means of suitatlle ~ ~ e g a l i v e feedt~acli. The sensitivity of this arrallgemer~t is a function of the overall p i 1 1 of the amplifier. T l ~ c crystal voltmelcr circuit is operated at n voltage h i ~ l 1 er1o11g11 to insure good linearity. 'l'hi. latter lea. ture allows use of a common metel.. such a s a 0-1 d. c. milliammeter. 1vit11- o ~ l t a special scale.

17igures 1.:: and 1--1. sl~olc. fested cir-

A ~ i n g l e - ~ ) o i ~ ~ t calibration of tile voltmeter will s~~flice, s i ~ ~ c e response is linear. 'l'he full-ccale point is the most r1esiral)lc. Apj)l y a krlowr~ 10-volt r. m. s. s i g ~ ~ a l to the i l ~ p ~ ~ t leads of the meter circuit he ~ ~ o w e r - l i n e f r e q u e ~ ~ c ~ will 1)e satisfactory) a ~ l d adjust the '

catil)ratiorr cot~trol poter~liometer to ,

bring the ~ ~ o i n t e r exactly to the l-milli- amper r point or1 the meter scale.

c l~ i t s for an~jllifier-reclificr type meters. 111 tach ca.e. he full-wave crystal voltmeter circuit is ca~~ac i tance-cor~pled to the an~[) l i f ier outllut ztage. A full

I [)ridge (4 diodes) is employed irl Fig- ure 1-3, and a hnl1-bridge 12 diodes) in Figure 1--1.. The full Ilridge meter has nl~proximately twice the sensitivity of t11e Ilalf-l~ritlge; however it requires four tliotlez wl~ich (for ]lest results) should have n ~ ~ ~ t c h e d ct~aracterislics. A Type 1N:?15 d ~ ~ a l diode In:iy be used in the half t ~ r i d ~ e ( 1 " i ~ u r e 1-4.) with two matched 1 0 0 - o h ~ n resistors..

Tllc ou tp l~ t ctage nlav he tile [lower tulle n o r r l ~ a l l ~ e n ~ ~ ) l o y c d il l tlre arnpli- her. In mozt o~r~~)l i f ier .< 1)11ilt esl)ecially for audio vo l~mete r 11-e. ho\vever. the o u t l ~ ~ t tube usllalIy is a triode-con- rlectecl hAK5 or GAQS ill a . c.-operated ur~its, or a t r i o d e - c o ~ ~ ~ ~ e c t e d SS4 in hat- lei-!.-ol~erated models.

AMPLIFIER lCCC T C Y T \

- -

Figure 1 - 3 . Full-bridge Tube-driven Voltmeter for Sensitive A.F . Measurements

VOLTAGE AMPLl FlER

AMPLIFIER (SEE TEXT) t--

Figure 1 - 4 . Hal f -br idge Tube-driven Volt-

meter for Sensitive A . F . Measurements.

111 eacll cil.c~lit (Figures 1-3 alltl 1-4): the electrolytic condenser sllo\vn in ~ a r a l l e l \\.it11 t l ~ e meter may I)e used or omitled. I I i t is used, dellec~ion o l the voltmeter \ \ , i l l he 1)roportional to the peak value or the applied signai voltage. If it is onlitted, [he dellectior~ of the voltmeter \rill I)e prol)ortional to he average valllcs of thv sigr~al roltagr.

T o calibrate a tube- drive^^ crystal \ oltrneter, apply an accurately-known a . c. voltage to tlle amplifier input and set the amplifier gain control lor desired meter deflectior~. I"or example, a 10-millivolt signal may he applied to the amplifier, and the gain set for Tull-

0-1 D-C MILLIAMETER

1 ELECTROLYTIC (SEE TEXT) I i l oon t-

scale deflecliou of the 0-1 r l ~ i l l i a ~ ~ ~ - meter. The metcr then \ \ t i l l read 0-10 millivolts. The procedure the11 is re- peated Tor e a c l ~ desired range of lhe meter. '1.0 s \ r i ~ c h rarlges at \\'ill, range resistors arc illstalled \vl~icli corre- spond in value to the resistal~ce seltings of lhe gain control tl111s deter lni~~crl .

1.3 HIGH-RESISTANCE CRYSTAL VOLTMETER

A common objection to the ordinar!, crystal-type a. c. voltmeter is its relatively low input resistance. This characteristic limits the instrument to measurements in low-impedance circuits if calibration accuracy is to be main- tained.

-

IN54A IN54A

A-C INPUT

Figure 1 -5. High-resistance Crystol Volfrneter.

'l'l~e i~~s t rurnen t resistance can he increased advantageously by use of a low-rarlge curretlt meter. The most sen- sitit-e ~nicroammeter obtainal~le i l l t l ~ c conver~tional ~)a r~e l - type case has a range o l 0-10 rnicroamljeres (AIarion 5 3 R N ) . This meter permits a voltmeter sensitivity or apl~roximately 100,000 ohms per volt. Figure 1-5(A) shows the circuit of 3 crystal voltmeter with sucll a desiral)le high input-resistance characteristic. Two high-back-resistance dioclcs ('I'ypc. I US1 4 ) arc. c.orl~~r.ctc.d i r r series to provide the high order o l rr- verse resistance required \\-hen higli-resistance multiplier resistors are to he 11sec1 i l l a voltmeter circuit. The basic circuit, a i .sllo\vn ill the 5ketcl1. gives lull-scale deflection of the n~ic roam- meter \\.it11 1h \.olt r. rn. 3. input. Be- cau.Ge of t l ~ e u l~usua l l \~ low current dcn- sity, resl)oll=e of the circuit is not linear a ~ ~ d a special meter scale or calil)ration c11art must he prepared.

Tlie rnultil~lier resistors required lor var io~ls voltage ranges must be \vorked

out e s p e r i n ~ e ~ ~ t a l l y by the builcler. since their exact values \\.ill depend upon the individual gcrmtlniurl~ tliotles used. The multi1)lier lor thr 1-I-olt range \\.ill be close to 88.000 ollnls: 988.000 olirns lor 10 volt>: 4.9 Inep ohms for 50 volts: 9.9 megolinls for 100 volts; 21.9 megohrnj Tor 250 volts; arid 39.9 rnegollms lor 500 volts. Re- cause of the estrenlely Iiigll values ol multiplier resistors required beyond 500 volts: it i j not advisable to extend the instrument range beyond that full- scale voltage. In a multi-range i11sti-u- ment, the multipliers may he switched in the conventional manner successive- ly into tlle circuit, as shown i n 1'i:ure 1-5 ( B ) .

The high-resistance voltmeter may be used at radio l reque~~cies . as well as at audio and po\ver-line lrequenciee The voltase source under teat must ~ 1 1 1 ) -

a d. c. return lor t l ~ e voltmeter circuit to allow the Ilotv of d. c. currenl through the meter.

1.4 SQUARE-LAW D. C. VOLTMETER

Square-lalv a. c. voltmeters have 1)een available for sometime. Similar instruments for experinlerltal d . c. operation are rlot readily obtail~able. A square- lalv d . c. \.oltrneterl in ~ \ . l l i c l~ meter dellection varies al)prosimatelp as the square of the at)I)lied \.oltager is useful lor checkirlg accuratel!. small \.oltage changes on a single meter scale. Volt- age changes: o l imporlant interest in certain tyl~es of experimelltal \i,ork, t l ~ u s lrccome more readable than on the comrnorl lillear d . c. vol~meter scale.

The non-linear res1)ol~se of a germanium diode at l o ~ v currellt densities may be utilized in the deve1ol)ment of a square-law d. c. voltmeter 1 ~ y employ. ing the diode as a series resislor in a simple meter circuit. The diode is C ~ I I -

~ ~ e c t e d to ]~:iss current i l l llle forward dirt~c.tiori. Ty[)c. 1N:11 4 gi\ tbs nl)[rroxi- 111atel y square-law respollsc i l l the fo r - \vartl vollage raage 0.1 to 0.2 volt. I t is necessary, therelore, to bias Llle diode positively to 0.1 v. and t l~en to apply he utllcrlo~vr~ (1. c. voltage in series \\.ill1 lllis hias. The re.-llorlse curve may l)e correcled to square 1a\v b\ mearls of a low value of linear series resistance.

I'igure 1-G is lllc circuit of a corn. plele square-la\\. d. c. voltrneler. Thc 1\:i 1.4 is 1)irisctl Lo 0.1 \ O I L [)o.;iti~.c~. tl~c- ooirlt at \ \ . l~ich sq~lare-lalv o11eralio11 slnrl.;, 1)y nleana of the vo l~agc divider I{,-I:,. Close a d j u s l m e ~ ~ t of this voltage is obtained by means of t l ~ e BIAS CONTROT, rlleostat, R,. Tn order to

keep the circuit resisla~lce low, so as not to reduce the steepness of the diode resporise cur\~e, the 0.1-\-olt bias is develol)ed across a 1-011111 resistor, R,. Also in order to keep the circuit resistance low, a lo\v-resistarlce indicating microammeter is necessary (100 ohms or less internal resistance). Since the 1 \:: I .A ( . I I I . \ t h i. - o r~~c*i \ ha1 .tc,csl~c>r t h u ~ ~ square law in the 0-100 microampere operating range, a $mall amount of series corrective resistance is provided in the circuit by the CURVE CON- TIZOL rheostat, I < , .

The circuit is adjusted i n the follow- ing manner: ( 1 ) Short-circuit tempor- arily the D. C:. INI'UT terminals. (2 ) Set rl~eostat I t , to zero ollms. ( 3 ) Con- nect a lo~\?-rauge (I. c. vacuum-tulle voltmeter or a 20:000 ollms-1)er-volt d. c. voltmeter across resistor 12,. (4) Set rheostat I<, for a 0.1-volt deflection of the test voltmeter. (5) T l ~ e microammeter will indicate alll~roxirnately 20 microamperes at this point. This is Lhe "false zero" of t l ~ e cr!.stal voltmeter (6 ) 1Zcn1ove the short circuit and apply arl acc~rralely-krlo\vn 0.1-volt d. c. po- tential Lo tile D. C. INI'UT terrnir~als. Observe the correct j~olari!y. ( 7 ) Note the rneler dellec~ion. I f tllis reading is not 8 0 microaml)eres ( lour Limes the false-zero readill;) ; irlcrease the resistance setting of rheostat R,, short-circuit he D. C. I S P U T lerminals, and reset rheostat I<, for 0.1 volt deflection of the test voltmeter. Kote new false-

CURVE CONTROL +o 5 0 ~ - WIREWOUND RHEOSTAT +

D-C INPUT ' 1 - 1

BIAS CONTROL - 7 LOW-RESISTANCE 0-100 D-C MICROAMMETER (GENERAL ELECTRIC TYPE UP-9)

~ I I I / ~ V (NO 6 DRY CELL) BOTH RHEOSTATS ARE RADIO VOLUME CONTROL TYPE

I o n WIREWOUND RHEOSTAT In.

Figure 1-6. Square-Law D . C . Voltmeter

ON-OFF SWITCH

I WATT

E3 -

zero reading. (8) Again, remove the short circuit and apply the 0.1-volt signal to the INPUT terminals, noting new microammeter reading. (9 ) When CURVE COKTROT. rlreojtat R , is e t properly, and BIAS CONTI<OL rheo- itat R, adjusteil lo r 0-1-volt hias, the application of a 0.1-volt in1111t l~oterl- tial ( r e p r e a e n t i ~ ~ g a 2-10-1 increa.se i r ~ diode voltage) will prod~lce a 4-10-1 increase in microammcler dellcclior~. 'r11e te3t voltmeter the11 rnny 1)e tliicorr- riected from across I<,. I f l l ~ e of~erntor. 1)rrfcrs that lt~ctcr tlcflection i tar t froni

rrleter zero rather than from a false- zero le\-el, he rnay buck out the false- zero clirrent I)y means of a d ry cell and rheo i ta~ .

Voltages in excess of 0.1 may be checked readily by means of n voltage divider with 0.1-volt output taps. \Whenever he instrument is l ~ o t in Iise. ollelr h e ON-01.'1*' switch, since the I ~ i t i i currc~rt drain tllrough resistors I<, arrtl I < , is 100 mi1liaml)eres. A No. 6 dry C C I I is necessary to supply h i s ~ m o r l l ~ t of cllrrrtll relial)ly a11d eco. no~nically.

1.5 6ALI.IS'rIC METER FOR SINGLE 'TRANSIENTS

INPUT 0

D-C V T V O L T M E T E R S H O R T - (SYLVANIA P O L Y M E T E R ) ClRCUlTlNG SWITCH ? T 2 5 V D C

Figure 7 -7 . Ballistic Meter for Single Transients

I. ' igl~~-e 1-7 -11o~vs tlre circuit of a sim- [)le rectifier-storage capacitor "front end" lor use ahead of a tl. c. vacuum- I I I I ) ~ voltmeter, s r~ch as llie Sylvania I'olylneter, to "catcl~" ral)itl, one-shot trnr~iit .~lts. Tlrc arrangemer~t shown will irltlic.atc a l ) l ) r o x i ~ l ~ a ~ c ~ l the peak val l ~ e of pc)sitive, 1ro11-rel'etitive pulses. Nega- I ivr I ) I I ~ . ~ C J call 1)e checked 11)- reversing [lie polarities of bolh the germanirlm tliotle and thc electrolytic capacitor.

A la.<t, 11ot1-rer~etitive ~)ulnc charges

111a1('1y to the 11ul.<e peak voltage. 'l'he large ca1)acitor l~ol t ls the charge due to 1l1 i . i voltage for an interval long elroupl~ to c ~ l a l ~ l e the 01)erator to read tlrc. n~cter . After the reading is ~akcrr, t11e . - l ~ o r ~ - c i r c ~ ~ i t i ~ r g sivitc11 is elo.<e(l 1110.

trrer~taril!; lo tli.<chnrge 111c ca1)acilor ir11t1 r e t r ~ r ~ ~ t11(: rr~ctcr to zero. The i l l -

~ t l . r ~ ~ r i c r ~ [ niay I I C calil)rnted for fa51 t ra r~s i rn t .~ i r ~ i t i i i l l ! . t11carr.s oi L I I I 05.

cilloscol)c Irnvit~y .I vol~apc-calil)rn~ed

1.6 SIMPLE A. C. MILLIVOLTMETER A .;i~nl)lt: a . c. millivoltmeter circuit

Tor a. I. aird r. f. measurements is i l ~ o w ~ ~ in 1"igure 1-8. The basic range or Illis circuit is 0-10 millivolts r. m. s. c ~ ~ ~ ( l a 5l~rcial l ea l r~re of tile circr~i t is its lit~cari~!.. 'This scrl.<itive raugc nlay Ije ex~c~ltletl 11y means of suitable multiplier resi.;lol.s connected in series wit11 11ie r~egative ~er rn i r~a l of [he microam- rneter. M r ~ l t i ~ ~ l i e r resistance values must be worked o ~ i t e ~ ~ ~ e r i m e n t a l l y ,

siuce their exact values will depc~ltl upon individual germanium diodes.

A~)l)roximatcly [\vice tile sl)erified -c-r~iitivity of 10 nlv. rnay be obtained I)y ernl)loyi~lg a .?.-diode bridge rectifier ir~;tc,ntl of the s i~ lg le diode sho \vr~~ i t 1 I:igure 1-8. It is important that tile tnicroa~nlneter have low internal resisl- auce; that is, 100 ohma o r less. Thc lal)or:r~ory-tyl)e (Icrleral Electric meter il)ecificd affords a srnsitivitv or 100

I N 3 4 A MICROAMMETER (GENERAL ELECTRIC TYPE DP-9, MODEL 8DP9AKKI)

A-C INPUT

I I

Figure 7 -8 . Series-type A.C. Millivoltmeter.

InicroL olta per scale dii ision. This is a relatively low-ilnpedancr

circuit. The output circuit of the voltage source under test must supply (I

d. c. return for the millivoltmeter circuit, otherwise the llow of d. c. from the diode and through the microarn- meter will 1)e 1)locked. No d. c. may be

present in the signal under measurement: other\vi+e erroneous deflection of the rneter will occur and the meter ant1 diode may be damaged.

When a high-impedance input is required, the millivoltmeter circuit rnay be preceded hy a simple cathode fol- lower stage.

1.7 TRANSFORMER COUPLED A. F. MILLIVOLTMETER

P U S H P U L L

D-C MICROAMMETER LINE TO PUSH- P U L L GRID TRANSFORMER

Figure 7 -9. Transformer-coupled A.F. Millivoltmeter.

Audio-frequency millivolts may Ije measured in low-irnpetlarlce circuits wit11 the millivoltmeter circuit s l~own in Figure 1-9. This a r r a n ~ c ~ n c r ~ t cm- ploys the high turns ratio of n line-to- p ~ i s h j ) ~ ~ l l grid translormer to stell thc lorv voltages u l ~ to values lligll C I I O L I F I I to actuate the diode and rnicroarr~rneter. A standard, p : ~ r c I - m o ~ ~ ~ t i r 0-50 d. c. ~ ~ ~ i ( , r o a r ~ ~ n ~ c , t c . r i.. ~ 1 1 - 1 . t l . I ' l l ( , 'I.\ 1 \ 5 0 \ ; ( ' ~ I I I ; I I I ~ L I I I I (lio(lcs ~ ) r o i ; ( I ( . - I I I : I \ ~ I I I L I I ~ rts(,ti l i ( ~ l ( , I I I , I . ( ~ I I ~ [or ;I y i \ iigllnl i111n1t \o l tn~c-.

I'ull-scale deflection of the rneter is obtairled with an i n p ~ ~ t signal of 10 to 15 millivolts r. m. s. An individual calibration m~ls t he made. The res1)nn.x is not linear al thol~gh i t is very ~ iear ly so. The transformer Inlist I)e a I~ igh-

quality u~ld io conlpor~ellt i lu\ l r~g wide frequency response if the instrument cali1)ration is to holtl throughout tlle audio soectrum.

I - The l~as ic range of the instrument

110 to 15 mv. lull-scale) may he ex- tended l)y means of appropriate multi- 11liers connected in series rvith the negative terrnir~al of the meter. 'rile resistance values of these multipliers must be worked out experimentally for the p r t i cu t a r diode artd meter used.

1Jse of the trar~slornler-coupled milli- vol~rneter shown here will l)c restricted to low-inlj~edarlce voltage .;ollrces (50 ohmi or Icss) . Wiler~ higll-inll)edunce i r l l ) ~ i t is required, the millivoltrrretc~ circuit nlay be I j reced~d ~ v i t l l a s i n ~ ~ ~ l e cutl~ode follo\ver.

1.8 AUDIO-FREQUENCY MICROVOLTER

""+ Y VOLTMETER CALIBRATION CONTROL 0-1 D-C M I L L I A M M E T E

Figure 1 - 10. Audio-frequencyMicrovolter, ,

Simplified Circuit.

This instrument is used to obtain known output voltages from a n audio oscillator and is useful for checking gain and other characteristics of amplifiers and associated equipment. A COARSE CONTROL rotary s ~ v i t c l ~ se- lects either of four outl)ut ranges: 0-1 millivolt, 0-10 mv., 0-100 mv.? or 0-1 volt. A FINE CONTROL potentiom- deflection of the rni l l ian~n~eter . ( 6 ) eter alloivs smooth, continuous varia- Mark the 1:lSE COSTI<OL dial 1 at tion of the output in any of the selected this 11oirlt. ( 7 j I<educe the ~ e t t i n g of ranges. The microvolter calibration is the FIXE CONTI<OL 1111til the v. t. standardized by feeding a 1-volt sigrlal i,oltmetel- reads 0.9 volt. 18) hIark this into the A. 1'. INPUT terminals. This point 0.9 on the FINE COI\'TI<OL dial. 1-volt refererice level is indicated by a ( 9 ) Repeat the procetlure at each lower I~ridge-tylle crystal L-oltmeter. 1 / 1 0 volt step d o ~ v n to 0.1 \.olt deflec-

The crystal voltmeter cor~sistj of a tion of t l ~ e v. t. voltmeter. and mark 0-1 tl. c. milliammeter, four matched each dial point accortlirlgly. ( 1 0 ) I<e. 1N34A diodes ( o r two 1 x 3 5 dual t l i - rnove the \-. t. vol~meter from the odes): and a screw-driver-adjusted circuit. meter cali1)ration rheostat. To adjust To use the tnicrovolter, feed the test tlle microvolter initially: (1) Feed a signal into the A. I:. IKPU'T terminals 11100-cycle signal into [lie A . F. INPUT and adjust the ou t l~u t of the signal tcl.mi~lals. ( 2 ) Set the FINE COX- source for center-scale dellection of the TI1OL ])otentionieter~ to its top (h igh- milliamnieter in tile micro\-oltcr. .4 de- rcsi-tance) positioll. ( 3 ) Conriect a sired output signal level tllen may 11e I~igh-resistance a . c. vacuum-tube volt- o1)tainetl Ly proper setlings of the meter I)et\~.een circuit ~)oirits X and Y. COARSE and F I S E c o ~ ~ t r o l s . For ex- 1 5 ) Adjust the ou111ut of the 1000- ample, 3 millivolts ou t l~u t is ol~taincd cycle source for a 1-volt deflection of by setting the FTSE COSTROL to 0.5 [he L,. t. voltnieter. ( 3 ) Adj~tst the and the COARSE control to X 0.01. \'OLTIIETEI( CALlBRATIOX COX. (This corresponds to 0.5 of 0.01 of 1 TROL rheostat for exact center-scale volt-or 0.003 v.. ~vhich is 5 mv.) .

X I O

900,ooon COARSE

X 0. I CONTROL - 9o.ooon A-F OUTPUT

XO.01

g o o o n

XO.001

l o o o n

- X

2 5 0 , o o o n

4)

250011 @ WIREWOUND

F I N E CONTROL

1.9 D. C. METER COMPRESSOR

Figure I . . 1 1 . D.C. Meter

'file simple compression circuit shown in Figure 1-11 alters the normally linear response curve of a d. c. milli- ~lmrnetcr in such a way that a small applied current produces a relatively large change in meter deflection, while larger current changes produce pro- gressively smaller differences in deflection. One application of a compressed meter of this type is as the null detector in a d. c. resistance bridge. In this application, the meter sensitivity to changes in current level increases as the null point is approached-a desir- able feature in bridge balancing. The "slowing down" of the meter response curve at high current levels also pro-

I

.5 - 0 I 2 3

D-C MILL IAMPERES INPUT

Compressor.

tects the meter against slamming when the bridge is unbalanced.

The respon-e curve in Figure 1-11 illustrates circuit behavior with a typi- c,al 1\:-11A tliotlc. u t l t l 0-1 (I. c.. r ~ ~ i l l i ; ~ m - meter. Respollse of more sensitive current meters, such as d. c. microammeters, may be compressed in the same manner. However, tlie meter series resistor (show11 as 500 ohms for the 0-1 milliammeter in Figure 1-11) must be determined exl)erimentally for the par- ticular microammeter used. The value of this resistor must be such that exact full-scale deflection of the meter is obtained at the maximum current input which will be encountered.

1.10 PEAK-TO-PEAK 'TELEVISION VOLTMETER PROBE

COMPLEX 1 N 5 8 A A-C INPUT

10 MEG --.

TO D-C V T VOLTMETER

1-f

I N 5 8 A I 0 MEG CATH _,CATH m

4 DIODES CONNECTED IN SERIES 0 . 5 ~ f d TO INCREASE VOLTAGE 4 0 0 V MIN IATURE HANDLING ABIUTY

Figure 1 - 1 2 . Peak-to-peak Television Voltmeter Probe.

'l'he amplitude of the coml)les wave- Figure 1-12 sholvs a typical crystal forms found in television receivers probe which can be connectecl ahead of may be checked successfully with a a d. c. vacuum-tube voltmeter, such as voltmeter only when the meter re- the Sylvania Polymeter. With this sponds to and indicates p e a k - t ~ - ~ e a k probe, peak-to-peak values a r e indi- voltages. cated by the d. c. scales of the meter.

All values a l~ove 5 vol~s peak-to-peak may be read directly from tile meter. Below 5 \ , O I L S I)-I): I~owever, a special calil)ratior~ must I)e rnade, since low- voltage no11-liriearity of the crystal diodes in this circuit causes the indica- tions to 1)e somewhat lo\c,er ~ l l a n true ~ ) e a k - ~ o - l ~ e a L values.

The 1)rol)e circuil consists of two shunt-~yl)e 1)eak rectifiers with heir inputs i l l parallel. One rectifier re- sponds to the 1)ositive half-cycle 01 al) j~l ied \rollage; ~ l ~ e other to tire negative 11all-cycle. The d. c. o u ~ p u t of each is equal to the peak value of the cor- resI'onding Iialf-cycle. The d. c. output circuits of the two rectifiers a re in series and thrrs are additive. Type 1N58

diodes, as s11o\vn ill Figure 1-12, permit measuremel~t of a rrlaximum input voltage of 200 volts l)eak-to-I)eak (70 v o l ~ s r. m. s., for a sine wave voltage). This maximurn may he doul~ led by ernploy- in8 1 1 4 ~ 0 ir~rivs-c.olir~ec:trd I N5XA's i l l

place 01 each single diode showrl. The insert in 1"igllre 1-12 sllo\vs proper polarity of collnections for seriea diodes.

The 1)eak-10-peal, I ~ r o b e may I)e 1)11 i l t inlo a >mall test ])rod wilh slrieldetl corllainer a i d shielded o~lt l )ut c a l ~ l e The terminal marked "x," should I)e connecled LO [he Lip 01 the pro t~e . All waveform,, illcludi~lg sinusoidal, rna) be measured wilh the probe and a 11igI1 resi-lance (1 c. v a c r ~ ~ l m - t ~ ~ l ~ e \ o l t m r ~ e ~

1.11 FULL-WAVE CURRENT METERS Cryslal-tyi~e a. c. milliammeters arrd microammeters, like crystal voltmeters, have the advantage of wide frequency response. E'ull wave current meters give the greatest sensitivity, since they uti- lize both cycles of h e measured current wave. Several circuit arrangements a re available for basic full-wave current meters. Figure 1-13 shows the four most satisfactory circuits; full ])ridge,

bridge, bridge, and 1/4 I~ridge. Response of each of these circuits is IIOII-lil~ear, requiring a special meter scale or calibration chart. A brief de- scril)tion 01 each circuit follows.

l.'ull Ur idgc . This circuit appears i l l

Figure 1-13 ( A ) . At full-scale deflection of the meter, the a. c. input current is approximately 1.1 l times the currenl value indicated by the d . c. meter. 1:or he>t results, the four diodes must have matched cllaracteristics, such as a 1N71.

:% Bridge . See Figure 1-13 ( B ) . At full- scale deflection of the meter, the a . c. input current is approximately 1.19 times the current value indicated by the meter. For best results, the three diodes must have matched characteristics. I n the absence of perfect matching of diodes, however, resistance R may be adjusted for equal-amplitude

~ u l s e s , as viewed or] tlle scree]] of an oscilloscope conr~ectetl across the d. c. meter terminals.

1/2 Bridge. See Figure 1-13 ( C ) . At full icale deflection of the meter, the a. c. input current is approximately 1.39 limes the current value indicated by he meter. For best results, the two diodes must have matched characteristics; although, in the absence of perfect diode matching, one of the resis-

D-C M I L L I A M M E T E R OR MICROAMMETER

( A ) F U L L BRIDGE

D-C M I L L I A M M E T E R OR MICROAMMETE

r - / I

A-C I N P U T

?

I & I

( 0 ) 314 B R I D G E

D - C M I L L I A M M E T E R OR .MICROAMMETER

A-C - (C) H A L F BRIDGE

D-C M I L L I A M M E T E R OR M I C R O A M M E T E R

0

I N P U T

0

( D l QUARTER BRIDGE

Figure 1 - 1 3 . Full-wave Current Meter Circuits.

tors may be adjusted lo r equal-all~pli- sistor is adjusted as described in the tude pulses, as viened 011 tlle scree11 three precedi t~g paragral)hs. The fol- of an oscillosco~)e c o r ~ ~ ~ c c t e d across lowill=; Table shows the maximum [he d. c , meter terrni~lals. value nhich each resistor can have.

B r i d g e . See Figure 1-13(D) . This circuit is u ~ ~ i q ~ l e i l l Illat i t pro\.ides lull-\vave rectificatin~~ \ v i t l ~ a s i r~gle diotle. Ho\vever, i t 113s tile lonest cl- ficiency o l ;Iny oi tlic circr~its givei~. 111 spite of its lo\v or i tpl~t ; economy zi~nlllicity. ar~tl co~~i l )ac t r~ess often \ \ . i l l clirtntc. its use. .At lull-scnlc tleflec,tion of lhe nrclel-. the a. c. input cr~rrent is al)i~roxinlateIp 2.78 t i~nes tile current \.slur i~~dica te t l 11y t l ~ r rilctcr. One or llle i111)1ll resistors 1n1l.t 11c adj~l- ted lor eqr~al-ainl)litr~de pr~l>cs, as viewed o t ~ t l ~ e scree11 ol all oicilloscol~e coil- tlecled across tile (1. c. 111e1er ter~ninals. lZ(~sisrors. ' h e resistors . = I I ~ \ \ - I I a t I I < ) , t C ) , ar~tl ( D ) i r ~ I'igrrre 1-l:i replace diodes in the 4,-arn1 ])ridge circriits. 111 ( C ) and ( D ) , these resistorJ are eq11a1 in value, excel)t \\here one re-

.Ilulliplic~d l<otcges. I I ig l~cr I . : I I I ~ C ~ rnny I)e provided lo r t l ~ e cry..lul-lyl)e current rncters 11y c o t i ~ ~ r c t i r ~ g all al1l)rol)ri- ate ~ I I I I I I I rwistor ( ' ; I c I I tlcsired rarlgr across t l ~ e A . i:. ISI'ITT t c r ~ n - inal.5. 'Tl~e rcsisla~lce or t l ~ c s11u11t 111us1 I)e sl~cli I I I ~ I t l ~ e c~lr l .e l~t llo\ving through i t \ \ - i l l lje t l ~ e dili'erence hc- I\vce~l the ~ o t a l c r ~ r r e r ~ t to I)c lneasured and the a. c. c11rrenl norrnally Iloiving illto thr crystal-~neter cirel~it.

1.12 SERIES-CONNECTED DIODES FOR HIGH-VOLTAGE A. C. METERS

Figure 1 - 14. Series-diode Arrangement for High-voltage A.C. Voltmeters

IN54A IN54A

~ s r A N c E 4~~~~

In simple, half-wave a. c. voltmeters for all voltages higher than 50 v. r. m . s., it is advisable to connect two germanium diodes in series for rectification (See Figure 1-14) . There are ~ \ F O reasons for this. First; high-vol- tape multipliers have high resistance values, and when this resistance is comparable to the back resiztance of a single diocle i r ~ a voltmeter circuit. rectification eaciency is reduced. Sec- ond, the trvo diodes in series are bet- ter able to withatand the high peak inverse voltages enco~~ntered . In a series-diode circuit, such as Figure 1-14? the increased lorivnrtl resistance clue to the second diode is negligible com- pared to the high resistance o l the

- & - 'CATH

MULTIPLIER I I I

0 5

mul~inlier. and does not detract from

+

. '

the advantage of increased back re. sistance. The 1 megohm resistor (shown in dotted lines) may be used to provide a betler return path for the meter circuit ~vhen the multiplier resistor is an extremely high value for measuring high a , c. voltages.

l ' \ - l ~ r . 1x5 !..A ir a s~)ctc,ial hirh-11ac.k-

< A-C INPUT ' l MEG c D-C MlLLlAMETER

, ' OR MICROAMMETER 0 1

I I -

. I

resistance diode. ~ h i i type has a resistance of at least 1 mezohm at -10

L

v. and is especially suitable for the circuit of Figure 1-14. Each diode in the Type IN35 dual unit likewise has at least 1 megohm resistance at -10 v. and this type provides both diodes for . . .

the series connection.

GERMANIUM DIODE INSTALLATION HINTS

1. Use the type of diode specified in the circuit diagrams. These types have been selected ca~.efully to with_;tand circuit voltages a n d other operating conditions.

2. When soldering the diode into the circnit. hold the pigtail leads with a pair of long-nosed pliers. 'l'hi.: will prevent heat from the soldering iron from cntering and poss~bly d a m a ~ i n g the crystal unit.

3. In all installations. use a s much of the pigtail lead length as possil~le.

4. While the Germanium Diode is a rug- ged component, the user is uilutiol~ed against

deliberately dropping the diode to the floor, tappinz on it. or otherwise handIing it in a rough manner so as to expose it unneces. sarily to mechanical shock.

5. 3lount thr crystal diode 50 that it is reazonab!! free from severe mecl~anical vibration.

6. Krep the crystal diode a far as poasil~le from heated object:.

7. Oilserve the diode polarity shown in the diagl-ams. T h e cathode terminal is plain. ly marked with l l ~ e abi~r-eviation "CATH" and with a wide l,and.

CHAPTER II

COMMUNICATION APPI-ICATIONS

2.1 IMPROVED LOW-LEVEL FREQUENCY MULTIPLI ER

3 LOW FREQUENCY INPUT

Figure 2-1. Improved Low-level Fre- quency Multiplier.

Several germanium diode ratlio-fre- querlcy m u l t i ~ ~ i i e r circuits have heen published in previous literature. Fig- ure 2-1 shows an iml,roved arrangement for multiplication at l o w power levels. In this circuit, two germanium diodes are connected in parallel with reversed polarity to pass current on diode used. This current \slur, 101. ex- both halves of an annzodulated r. f . ample, would he 100 ma. Tor two T!11c. cycle, and are tapped down the input lN:32A's. 120 ma. Tor lN56.4'~. c.tc,. and output taiik coils fo r improved J lasimum frequency multiplying efi- impedance matching. This circuit util- ciency will be obtained at low current izes to the fullest advantage the non- levels (meter readings of 1h milliam- linear (distorting) characteristic of the ,,ere and under) , t l ~ e region in which diode response curve to produce llar- diode non-linearity is greatest. The two monics of the input frequency. diode.; need not be matched; in fact

The input tank, LIC,, is tuned to the rnr~ltilrlying action is enhanced some- frequency of the input signal. The out- what II! mismatch. put tank, L,C?. i tuned lo the desired F ' l~i le the germanium diode fre- harmonic. The diodes a re tapped from quency multil,lier is a low-power de- 1/2 to 1/3 tile way up from the grouncl- vice. it nevertheless \ \ , i l l find applica- ed end of each tank coil. A radio-Ire- tion in high-sensitivity transmitter quency milliammeter may be inserted exciters and in other experimental at the meter jack to check current cqui l~ment \\here frequency multipli- t l~rough the diodes. This current mr~.;t cation can be carried out a t low power not exceed twice the average anode levels ahead of higll-gain pentode or current recommended for Lhe type of heam power amplifiers.

2.2 HARMONIC ACCENTUATOR FOR EXCITERS I N 3 4 A .-'

CATH FREQUENCY M U L T I P L I E R

PREVIOUS EXCITER S T A G E ---

Figure 2-2 . Harmonic Accentuator for Exciters.

Figure 2-2 shows how a pair of ger- multiplier stage is increased. This ar- manium diodes may be connected in rangement is particularly favorable to the grid circuit of a frequency multi- odd harmonics (3rd, 5th, etc.). Grid plier stage in a transmitter to raise resistor bias is shown in Figure 2-2, harmonic outp~it. By distorting the but the scheme may be employed also grid current fluctuations and thus em- in multiplier stages which employ bias- phasizing harmonics in the r. f. exci- voltage supplies or cathode resistor tation voltage, the effectiveness of the bias.

2.3 SIMPLE CllElNG RECEIVER -1 HEARING-AID EAR-PIECE

Figure 2-3. Simple Cueing Receiver.

Where the surrounding noise level is not excessive, a stage manager or pro- gram director on the sidelines with a m u

portable u. h. f . radiotelephone transmitter can "cue" actors or announcers

receiier may be Carrie2 in a pocket mF or hidden in some convenient part of

The information in this book is furnished without assuming any obligations.

14

a co5tume, need no1 1 ~ e any larger than a 1)ook of safely matches, and the two shorl lengths of flexible insulated wire which co~npr i je tlle "dipole" ar~terlnci rnay be stretclled 1)) -titching converi- ier~tly irito the costume. The antenna length is not particularly critical, a useful amount of eiiergy being picked up by brute force from the nearby transmitter. A foot or so oI lenglh irl each section usually will sufice. The number of turris i r i the r. f. chokes ~vill

deperid upon the lmnsn~il ter Irequen- cy. A rule of the thumb is to nieas~ire off ( for each choke) I/; wavelength of S o . 30 cotton covered wire and wind LIVO closewound coils on insulated rods or sticks allout the same diameter as the germanium diode.

At noisy locations, ou tpr~ t of the cryslal cueing receiver rnay be fed into 3 converitional hearing aid as n hoost- r r audio amplifier.

2.4 AMPLIFIER PROTECTIVE RELAY

2 OR 3 TURNS OF INSULATED HOOKUP CATH.

WIRE (SAME DIAMETER -001JJfd AS DRIVER TANK COIL) 5 0 0 0 V MOUNTED RIGIDLY NEAR M I C A TANK COIL .

10,000 n 2 MA. WIREWOUND

POTENTIOMETER RELAY RELAY A c

Figure 2 -4 . Amplifier Protective Relay.

The scheme shown in Figure 2-4 pro- tects a grid resistor-biased beam power amplifier in a transmitter against dam- age due to loss of bias when excitation fails or drops to a low level. Since the protective circuit is operated by r. f. &ergy from the exciter, it is controlled directly by excitation level. This arrangement allows the advantages of resistor bias to be utilized with complete protection.

A small amount of r. f . energy is picked up by the coupling coil mounted rigidly near the driver plate tank coil. This energy is rectified by the 1NS4A diode and the resultant ti. d usrd to hold-in the sensitive d. c. relay,

IiY-1. The setting of the 10,000-ohm potentiometer and the coupling coil spacing both a re adjusted by trial so that the relay RY-1 opens when the amplifier grid bias drops to the mini- rnuni permissible voltage level. Relay RY-1 in turn controls a 115-volt a. c. relay, RY-2, which removes plate and screen voltage from the amplifier whenever excitation falls to the level corresponding to minimum permissible grid bias. Both of the relays a re normally open. Although a single-ended amplifier capacitance-coupled to the driver is shown in Figure 2-4, the protective relay scheme may be applied a s well to pushpull amplifiers and to other methods of inlerstage coupling.

2.5 CARRIER-OPERATED RECEIVER MLITING SYSTEM

! PICKUP ANTENNA 2 TO 5 MA. I I

I N 3 4 A D C R E L A Y TO RECEIVING ANTENNA

-. D. P D. T. 'CATH. NORMALLY OPEN 0 A N T -

-- /

L C 0 GND. - - MICA OR

0 - RECEIVER CERAMIC " -

? rn

1 = L AND C TUNE T O T R A N S M I T T E R FREQUENCY

Figure 2-5. Transmitter (Carrier) Operated Receiver Muting System.

In Figure 2-5, the transmitter carrier is rertified by a 1N34A diodr arid thr resultant d. c. applied lo a sensitive relay. When the relay closes a s a result of the carrier coming on. one pair of its contacts short-circuits the antenna input terminals of the receiver. while the other pair short-circuits the loudspeaker voice coil. This scheme eliminates the usually heavy-duty transmit-receive switch or relay system, and is particularly applicable to a receiver which must be located at some distance from the transmitter. Since this arrangement permits the

receiver to operate continuously a t its riormal voltages. s tandl~y drift is elim- inated. When the transmitted carrier is interrupted: the receiver autornati- cally is recommissioned. Modulation does not affect the relay.

Coil L and capacitor C a re chosen to resonate a t the carrier frequency. In the ileighborhood of a transmitter of reasonable power, sullicient energy may be picked up without an antenna. Farther away, a small pickup antenna will be required. This may be a random length of insulated wire o r a short vertical rod.

2.6 VOICE (MODULATION) CONTROLLED RELAY RSTAGE AUDIO NCCADLICD

MICA n I U N D I

I I I

1 0 0 0 f l f d . 5 0 V. 1 E L E C T R O L Y T I C

1-2 MA D.C RELAY

A TO CONTROLL- ED DEVICE

- - Figure 2-6. (Voice Modulation) Controlled Relay.

Voice-controlled systems depend upon control action obtained with the modulation component of energy picked up from a modulated transmitter. Such systems operate only while modulation is present and release in the absence of modulation. Presence of the carrier component has no effect. Typical applications are voice-controlled receivers, instruments, switching devices, etc. associated with the transmitting station.

E'inr~re 2-6 shows a simple voice control receiver which is small enough to be built into a n inconspicuous box. The coil-capacitor combination, L-C, is tuned to the transmitter carrier fre- quc2~rc.!.. 'l'hc. 1\:2'1.4 nc.1~ as a drtt,c,tor or demodulator. The modulation com- ~ o i ~ , ~ ~ , t ~ I ) t a i l ~ t ~ t l I ) ! 111c~il11c 01 thtt 1 x 3 1.4 is passed by the coupling transformer

to the 1 8 3 6 which acts as a modulation rcLc l ~ f ~ r . r . I ) . (.. outl~lrt of thc, I \ 50A i h

applied to a 1- or 2-milliampere d. c. relay \\Iiicli accordingly is picked up as a result of presence of modulation.

The length of time the relay is held- in after n~odulat ion ceases may be controlled by the 5000-ohm potentiometer and 1000-microfarad electrolytic capacitator sliunting the relay coil. The less res i s ta~~ce cut into the circuit by tlie potentiometer. the faster \zill I)e the relay dropout. and vice versa Thus. the potent io~r~eter may be set at one extreme to drop the relay out after each ordinary spoken \cord, o r a t the other extreme so that the relay holds-in for several seconds after speech modu- lalion ceases.

2.7 MONITOR RECEIVER FOR BROADCAST TRANSMITTER LOCATION

, - S H O R T PICKUP A N T E N N A

I N 3 4 A 0 l ~ f d

I \ AUDIO A M P L I F I E R

5 0 0 0 L O U D S P E A K E R n

I ' - T Y P E R - 3 0 0 ) 0001 p f d - M I C A OR -- - C E R A M I C

Figure 2-7. Monitoring Receiver for

Broadcast Transmitter Location.

l'or continuous aural monitoring (via loudsl~eaker) of a broadcast station straight fro111 the air, a simple crystal " f r o l ~ t end" may be coupled to a small audio amplifier. Details of this ar. cover the 500-1600 kc. range. Tuning rangernent are sho~vn in Figure 2-7. capacitator C can he a miniature air

A short picktlp antenna, consistin: trimmer pre-set to the transmitter fre- of a vertical rod or a random length queiicy. If frequencies higher than of inslilated ~c i re , is all that is required 1600 kc. must be reached, a few turns \ v i t l l tlie receiver to deliver a hujky may be removed from the 1-millihenry. audio signal to the amplifier input r. f . choke, L, to obtain resonance. terminals. The L-C tuning cotnbination The audio aml~lifier need not he bulky specified ill Figure 2-7 is designed to nor complicated: since the a. f. output

of the diode detector will I J ~ high in is good. Sensitivity o l the receiver is the neighborhood of the transmitter. low; but this is an advantage, since One voltage amplifier stage and a sin- reduced sensitivity prevents pickup of gle power o ~ ~ t p u t stage usually will illterfererice from other stations on the sufice. The amplifier call be of the same frequency and also from nearby AC.DC type if economy dictates. "static" sources.

Audio fidelity of the diotle detector

2.8 A. M. RECEIVER NOISE LIMITER 8 + 2 5 0 V.

+&+To AUDIO OUTPUT

0 l y f d

0 5 MEG. INPUT GAIN CONTROL

DIODE

330,OOOIL 3 0 0 0 l l

CATH CATH.

STAGE

Figure 2-8. Impulse Noise limiter

.4 cun l l~ ina t i o~~ series-shurlt aritomatic c.o~rl!)o~~t,r~[ i. a 1 L.5 1.4 tliotlt.. 'l'hi. I! I N '

im l~ r~ l s e noise limiter for A. RI. re- has I ~ i ~ h 11ack resista~lce \vhicll adaots c e i ~ e r s is shown i l l Figure 2-8. This it to this j~osition in tlre c i r c ~ ~ i t . The circuit is arranged around the corn- shu~l t clil~ljer coml~orlmt is a standard }lined 2nd detector-1st audio stage of I \:i 1.4 clioclc.. 'l'hc. c.ir,,uit i. >,.If-atljuit- the receiver, requires iew parts, and ill;: to the nocrclgc level of t l ~ e inter- is quite compact. Thr series clipper r~~etl iate-Lrcqr~enc~ sipnal.

The information in this book is furnished without ossuming any obligations

CHAPTER Ill T. V. AND RADIO SERVICE DEVICES

3.1 T. V. ANTENNA ORIENTATION

250,u,ufd SENSITIVITY - - - - - - CONTROL

-1

I N 5 4 A SHORr lNG I SWITCH

I ( S M A L L

TO RECEIVER 4 0 0 V ( O . 0 0 2 p t d CHASSIS MICA I I -

- : E A R T H GROUND L-- ---- 1

Figure 3-1. T.V . Antenna Orientation Meter.

A meter giving peak deflection when a televibion receiving antcnna is lined "11 prol)erly wit11 tlre trari-n~ittirrg station is invaluable in a n t c n ~ ~ a installa- tiori \ \or k. Figure 3-1 shows [Ire circuit diagram of an anter~na orientation rnetcr 01 tliis type.

l'hc l'V51A diotle arid the t ~ o capa- citors a r ~ d one resistor a.ssociated with i t may be enclosed in a small probe. Conr~ections from the diode pickup circuit a re made to the receiver chassis and p i r t ~ ~ r e - t u b e grid. (The picture-

L L I I I ~ cat l~ode must he ~ ~ s e d if [he video 4gr1al is nl)l)lied to the cathode in the r c c e i ~ e r u-cd). D. C. o u ~ l ) u t from the cliotle is Ietl t l i r o ~ ~ r l ~ a Ilcxible coaxial c a l ~ l e to the roo1 top \vl~et-e the antenna ill-tallation is beirig made. The receiver is ~witcl~etl-or1 all(] t~iilcd carefull\ to 3 desired clian~rel Irequet~cy.

11s the anlenna is rotdtcd, tlie rneter reading will iricreaae as tlie aritenna hecomes aligrieti \ \ z i t 1 1 the station, and will be r n a l i n ~ ~ ~ m \vheri the antenna points directly tolvard the signal

sol~l-ce. Ghosts :tio\v up as double of the meter. When t l ~ e recei1-ed signal peaks as the antenna is rotated. The is too weak for full-scale deflection, 2-rnegohm SENSITIVITY CONTROL the rheostat may be cut out of the cir- rheostat allows the signal voltage to be cuit by closing the short-circuiting cut down at will to prevent :lamming ~ \ ~ i t c l i .

3.2 SELF-CONTAINED FIELD STRENGTH METER

Tile antenna orientation meler described in Section 3.1 requires connection to a working television receiver. It also necessitates running a cable from inside the building to the roof. For the same purpose of antenna ad- justment, self-contained field strength meters a r e available, but these instruments a re 115-volt operated and have the disadvantage that a power line for their operation must be pulled to the roof.

A self-contained field strength meter operated free from the power line and requiring not even batteries may be made with a germanium diode detec-

tor. Suc l~ an i n s ~ r ~ ~ r n e ~ i t consists sini- ply of a tuned circuit (tuneable to the desired t. v. channel frequency) connected to the crystal millivoltmeter described in Section 1.6, Chapter 1. The antenna is coupled into the coil of the tuned circuit by means of a small coil connected across the con- ductors of t l ~ e feeder line. The feeders also may be connected across a fen turns of the coil.

The tuning capacitor may be a 100- uufd. air variable Coils for the various channels may be wound from data on coil specifications found in the various radio handbooks.

3.3 DEMODULATOR PROBE FOR T. OSCILLOSCOPE

2 5 0 p p f d

TEST PROD MICA 2 0 , o o o n

I \ 1

T W T

TO CHASSIS RECEIVER l N 3 4 A ~ c A T ~ 0 1 0 0 0 ~ ~

F L E X I B L E CONCENTRIC

------ TO OSCILLOSCOPE VERTICAL AMPLIFIER INPUT

LTO OSCILLOSCOPE GROUND

Figure 3-2. Demodulator Probe for Oscilloscope.

Visual alignment methods a re required Figure 3-2 shows the circuit o l a in television servicing. Khen an oscil- demodulator pro],e eml,]oying a Type loscope is used in the alignment and 1$:3-1.A diode. All of the ~ ~ o ~ n t ~ o l l c ~ l l ~ ~ tezting of television r. f . , i. f., and Inay be enclo5ed in a shicldcd-llandle sometimes video stages, the high-frequency signals must be demodulated test prod. The cable may be made up

before presentation to the am. to feet in length belore shuntin:! plifier of the oscil~oscopc. A german. capacitance becomes objectionable, ium diode circuit is employed however: this cable should be kept for demodulation. as short as f~rac t ica l~ le .

3.4 TUNED CRYSTAL-TY PE SIGNAL TRACER

SHIELDED PROBE

( ~ f l f l f d CERAMIC 1

HIGH GAIN AUDIO A VOLTAGE AMPLIFIER

-0 -- -- -1 /-.

OUTPUT GROUND CLIP INDICATOR

(TO RECEIVER CHASSIS)

cor L (L) VALLIES 4 0 0 - 1 2 0 0 KC 90 TURNS NO 3 2 ENAMELLED WlRE CLOSEWOUND ON 1 v4" DIAMETER

FORM. TAP I 8 TURNS FROM BOTTOM END.

1100-3200KC 5 6 TURNS 1\10 3 0 ENAMELLED WlRE CLOSEWOUND ON 5/8" DIAMETER FORM. TAP 12 TURNS FROM BOTTOM END

3 - 1 0 M C 20 TURNS NO 3 0 ENAMELLED WlRE ON 5/8"-DIAMETER FORM. SPACE TO WINDING LENGTH OF 1346. TAP 4 T H TURN FROM BOTTOM END.

8 - 3 0 MC 6 TURNS NO 24 ENAMELLED WlRE ON S/$ - DIAMETER FORM. SPACE TO WINDING LENGTH OF 518". TAP 2ND TURN FROM BOTTOM END.

Figure 3 - 3 . Tuned Signal Tracer

Signal tracers are justifiably popular lor tracking down trouble in radio receivers. An amolitude-modulated lest signal is used in the signal tracing operation. RIost $imple signal tracers consist of a cr);slal-tyl~e demodulator l)robe connected to the inpr~ t c i r c ~ ~ i t ol a higll-gain audio voltage aml~lif icr . .An oull)ut intlicator. S L I C ~ as a11 a . c. voltmeter, headl~hones? or magic eyc tube, 31101~s relati\.e si,nnal stre11gt11 (or absence of signal) a t various t e t points. Worth\\.l~ile improvement is obtained ~ \ , l ~ e n t l ~ e s i ~ n a l tracer can be tuned to the carrier Ircquency of the lest signal. 1 ) 1 1 t conve~~tional tuned signal tracers (channel anal!.zers) con- tain many tlll~es and are both complicated and exl~er~si i -e .

Figure 3-3 shows a simplified. tuneable signal tracer. The input stape emhodies a single tuned circuit and 1 1 3 14 detector. This is, in effect. a

crystal ~xceiver. The explorir~g test prod is connected to the tuned circuit through a 2-unId. capacitor which serves to isolate t l ~ e instrument from the circuit under lest and from the oI)erator's fingers, thereby preventing tlctuning of lested circuit. Output of t l ~ e diode detector is fed into a high- gain audio amplifier terminated by an output meter. For a. C. operation, the amplilier may consist of a resistnnce- coupled GAU6-6AQS c o m l ~ i ~ ~ a ~ i o n . For lull);-portable hattery operation, a lU4-3% resi5tarlce-coupled lineup rnay I>e used.

T I I I I ~ I I ~ of the signal tracer is accom- plished by means of a dual S65-ur~ld. iniclget \,nriahle capacitor \c.ill~ its two seclior~s connected in ~ ~ a r a l l e l . The complete tuning range is 400 kc. to 30 1Ic. in lour ranges: 400-1200 kc.? 1100- :3200 kc.: 3-10 hIc.. and 8-30 hlc. This range inclr~des all i . f.. r. 1.: and oscil-

lator frequencies ordinarily encoun- rated by feeding-in modulated signals tered in the servicing of radio receivers. f rom a signal generator, and can be The coils may be I \ . O L I I I ~ ~ frorn instruc- graduated directly in kilocycles alld tions given in Figure 3-3 or may be commercially available all-band coils. They may be made plug-in for range In addition to its intended use as a

changing, o r a rotary selector switch tuneable signal tracer. this instrument

may be used with self-contained may be used '0 check r. f . test f o r band switching. The dial attached oscillators and signal generators, trans- to the tuning capacitor may he ~ a l i h - mitters, and carrier cor~trol equipment.

3.5 TELEVISION VlDEO DETECTOR

L A S T VIDEO 20 ,000 n I-FAMPLlFlER

1 0 0 y ~ ~ f d I N 6 0

1 2 0 y h VlDEO OUTPUT (SYNC. NEGATIVE)

TO VlDEO AMPLIFIER

BANDWIDTH 4 MEGACYCLES

Figure 3 - 4 . High-efficiency Video Detector.

. \ \ \ ,

The lower dynamic impedance and in- 111 Figure 3-3.: a video detector cir- creased e k i e n c y of the germanium di- cuit is desigr~ed around the Type lN6O ode reco~nmer~d use of this component which is a video detector diode, in a numher of circuits in place of the c i rcu i t constants are lor 4.mega. usr~al diode tubes. Other advantages cycle Landwi~lLl l . ohlained at the same time are com- pactr~ess, heatless operation, low shunt Improved receiver [)erlormance has

cal)acitance, silnl,le \,,iring, and elimin- been reported 1)y service technicians

atiorl ol f i l a m e n t j , A typical applica. and by experimenters who have incor- tion is ~ 1 1 ~ ger.nlallirlm diode \ideo de- porated this video detector into t. v. I ~ c t o r lor television receivers. receivers.

TO OBTAIN ALL TYPES OF SYLVANIA GERMANIUM DIODES SEE THE SYLVANIA ELECTRONIC PARTS DISTRIBUTOR NEAREST YOU. YOU WILL FIND HIM LISTED IN THE YELLOW PAGES OF YOUR TELEPHONE DIRECTORY UNDER "TELEVISION SUPPLIES AND PARTS."

3.6 F. M. - T. V. DISCRIMINATOR 2 l f i p l d

I O O g g f d

100,ooo TO AUDIO AMPLIF IER

AMPLIFIER

100,000 n

STANDARD DISCRIMINATOR TRANSFORMER

Figure 3-5. F .M . -T .V . Discriminator.

The irnl~rovetl lor\card and reverse provising. charac~eristics of he ~ w o matched di- This discriminator rnay be employetl c~des in the Type 1N:iS dual diode unit in regu la r 1:. ~ 1 . receivers, as well as are exploiled lully i l l the simplified in sound channels in televisiori recei\.- discriminator circuit show11 in Figure :3-5. The increased reverse resistance ers. If a pair of malched 100,000-ollri~

of the 1 ~ 3 5 a l l o w s l t l e use of lhe high resistors is used. IIO adjustrnents wi l l 1 100,000-uhrn) load resislors f o r hest he required heyorld the usual align- c i r e ~ ~ i t t~lliciericy and \vilhout any im- rtient of the iriput translormer

3.7 F. M. DYNAMIC I.IMITER .AST I-F APLlFlER

7 L

Ah STANDARD RATIO DETECTOR

TRANSFORMER

TO RATIO

10,000

DETECTOR

Figure 3-6. F . M . Dynamic Limiter.

I:igr~l.e :i-6 shu\\, a germanium-type dy~lanl ic limiter which has none of the cornl)lesity of tube-type stages of the iame Lype. This circr~it may l)e al)l)lied il l I'. Rl . receivers rrntl t . v. sound cha11- r~els. 'l'l~e thresl~old level is variable :III~ reaches low si;~~nl let-els. Inter- c,l~ar~nel I)ack;l.o~lt~d troiae, as well as audio hrlzz i l l it~terc:rrrier-type televisiori receivers. ~11.c cluietcd I)y this limiter circuit.

Chic.1 fraturc. ol tht, limiter is the scsll- 1)iasc~cl 'T!.l)t. 1N56A h i g h - c ~ o ~ ~ d r ~ c ~ t i o r ~

diode tvhicli i b c o n ~ ~ e c t e d i r ~ 1)arallrI \vilh the I)rinrary of the t l e ~ e c ~ o r in1111t translorrner (rat io detector o r discrir~l- inator) . Diode hias i.q develol)ed across the 10,000-ohm diode ~ e r i e s resistor. T l ~ e sl~rrnling ca1)acitor is a 10-microfarad electrolytic. Tile time constant of ~ l i i s I<-C comhir~alion is satisfactory for reject ion of a m ~ ) l i t u d e - m o d u l a t e d lnultipath interlerence coml,onents, GO- cycle blar~king prrlsea~ and similar l ~ l ~ e n o r n e r ~ a .

3.8 T. V. CASCADE SYNC CLIPPER L A S T VIDEO

TO PICTURE b TUBE CATHODE

3 3 0 0 f L

Figure 3-7. T.V. Cascade Sync Clipper.

A high-level sync clipper is shown in Figurr 3-7. The tuo c,aic,ndrd I L.3 IA ' - in thls c ~ r c u i t a re supplied with fixed bias partially derived from the plate load resistor of the last video amplifier. The biasing network for each diode has a long time cor~stant. The high- frequency con~pensation of the video output stage is unaffected by shunting

the c l ip l~er circuit across this output, I~ecause of the 10iv diode capacitance.

Stripping action of the two diodes is cumulative. sillce the clipping level of the second diode is determined by the partially separated sync pulse output of the first diode. Separation is sharp, and sync pulse output o l the clipper is completelv free o l video information.

3.9 A. G. C. PEAK DETECTOR L A S T VIDEO TO PICTURE TUBE AMPLIF IER (GRID OR CATHODE DEPENDING

UPON PHASE OF L A S T VIDEO TO SYNC CLIPPER A M P L I F I E R )

B+ f250V. +375V - 5 5 V

Figure 3-8. A.G.C. Peak Detector and Amplifier for T.V.

In the circuit of Figure 3-8, a lN34A, control grid of the A. G. C. amplifier direct-coupled to the plate output of tube. the last video amplifier: is used as an The control rate of the circuit takes A. G. C. detector. This diode conducts care of all but very fast fading; how- only during the sync interval because of the lengthened discharge time con- ever the receiver gain does not alter

stant of its load circuit. ~h~ appreciably during vertical blanking d. C. voltage output of the diode detec- periods, so vertical sync pulses are not tor is R-C filtered and presented to the "pushed down."

3.10 T. V. VERTICAL PLllSE SEPARATOR

0 OOlpfd 0 0 0 1 p f d ,,,, FROM 4 I N 5 4

AMPLIFIER

- -

6 8 0 0 fi

- - - - I?I 0 i

TO VERTICAL

OSCILLATOR

Figure 3-9 . T.V. Vertical Pulse Separafor with l imiter-Inverter

4 t,iacc-tl 1 \.5 1 .4 tliodc. in thcl c.il.c.uit output pliises a re steep-fronted, of h i g l ~ showrl irl Figure 3-9 follows a %stage and I ~ o s i ~ i \ ~ e in tlilrerentia~ing network, and clips hori- p hi^ circuit s~al , le ,.crtical syrlc zontal ComPonents ''om ''1' al)l'lied minuj in,erlace jitter rllld l i n e pairirlg, sync signal. The negati\fe vertical The low interelec~rode capacitance of pulses in [he diode output then a re applied to [he of a triode which am. L I I C . 1 \5 1.4 irlll)t.o\(>- I ) L I I S I tli.\c.,r-in~irln-

plifies, squares, and inverts them. The tion.

GERMANIUM DIODE INSTALLATION HIIITS

1 U5e t11e type of diode specified in the circuit diagrams. These types have been ~ c l e c t e d carefully to ~\.itllctand circuit vol- ta,ncs and other operating con~1ition.i.

'7. When soldering the diode illto t h r circuit , hold the pigtail leads w i i h a pair of l o n g - n o d pliers. '['his ~v i l l prcvrnt heat from the -oldering iron from entel-in: and pojsihly damaging the cr!.stal nnit .

3. I n all installation;, use as n i l~ch of ~ l ~ e pigtail lead length as pnssil~le.

4. Whi l e the Germanium Diode is a rup- zed component, t l ~ e user is car~t ioned apainst

deliberately dropping the diode to h e !loo:, tapptng on it, o r otherwise l~ond l ing ~t In a rough manner so a s to expose it unneces- sarily to mechanical shock.

5. h1011nt the crvstal diode so h a t it is reasonal)ly f ree from s e w r e mechanical vibration.

6. Keep the crystal diode a s far a s possiblr fl.om heated objects.

7. OlJserve the diode polarity shown in the diagram;. T h e cathode terminal is plain- ly marked with the al>l>revin tion "CATH" . ~ n d wilh a \vide band.

CHAPTER IV

EXPERIMENTAL APPI-ICATIONS

U N M O D U L A T E D R-F INPUT

d d A U D I O INPUT

Figure 4-1. Germanium Diode Ampli-

tude Modulator.

A simple arnl,litude n ~ o d ~ i l a t o r wilh a hosl o l applicatior~s in Lesl inslrilments a r ~ d elcclror~ic c o ~ ~ l r o l gear is S ~ I O \ Y I I i l l

12igure .I.-1. \ Y ' i l l ~ a rnir~irnunl o l corn- ponenls. this circuit utilizes he a1)ility of a norl-linear c o t n l ~ o ~ ~ e n t such as the I \:3 14 ;er111;111iun1 ~ l i o ~ l , ~ 10 ac , ( ,on~l , l i~ t~ rnodulalior~.

111 a typical al)l)licalior~, unmodu- laled r. T . Trorn an o~c i l l a to r or sigrial gc~ierator is Ted i t ~ t o one 1)air of input tern~iilals, and iiri audio m o d ~ ~ l a ~ i n g signal inlo the second pair of inpi11 terminals, Aml)litude-modulaled r. f . theri is available at the output terminals. The wide frequency range afforded k,y the germanium diode also permits the modulation of one r. f. signal by another r. f . signal, or m o d ~ ~ l a t i o n of o r ~ e audio signal 11y another audio sigllal.

The diode rt~odulator may be em- [bloyed for eslernally modillatir~g a 5ignal generator, lor ~ ) r o d l ~ c i r ~ g arnpli-

A M P L I T U D E - MODULATED R - F OUTPUT

tude rnotl~rlulion at low l)o\ver levels i l l

radio arid carrier-current transmitters. tone-modrllaling received signals (by inserting the modlllalor in he i . I. am. " - .

plifier of a recei\.er), and lor prodiic- ing a modulaled ("t\vo-tone") audio test signal lor special amplifier clieck- ing. Since I I O cou l~ l ing transformer i i preserit i r l he rnodulation illput circuit, higl~.modulat i r~y lrequencies extending 1 I I r. 1. spectrum may be used \\.it11 ease. ' h e diotle modulator can be operaled ; i t ~ ~ I f r : l - l ~ i g l ~ frequencies, il desirecl.

iivc. - to-way · introduction in this booklet, we preserll '10 gernlaniurll diode...

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