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Tn Ii?' 3;T16. 11-239 /~

RliSTRICTIW ....

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WAlt DEPARTMENT, W".H'''''TOI<, 4U1U"t 14, UNL

RADIO SET SCR-203

P_ ......... 41 •• nl •• 01 ... 0010' Sinal _

s.,UON I, General de&eription. ... ..... " 1rype. ______________________________________ 1 Power __________ ______ _ __ __ __ __ __ __ __ ___ __ __ 2

Nature of trall9mi!!8ion and reception_______ __ 3 Distance ranges________ ___ ____ _____ __ ___ ____ , Frequency range_________ ___________________ 5 Channels. ___ __ ____ ___ __ __ ___ _ _ _____ __ ____ __ 6 Weight and splce_________________________ __ 1 Trall9port-____________________ . _. __ ____ ____ 8 VIII! _____ .____________________ _____ ________ _ 9

Component parts ______ __ ____________________ ' 10

Radio transmitter BC-228 or BC-228---A _______ 11 Radio rtlCiliver DC-227 or BC-227- A__________ 12 Ramo control box BC-235 or BC-235-A_______ 18 Generator ON-35_______________ __ ________ __ 14, Do:.: BX- 12 or BX- l2-A___ ___ __ ____________ Hi Mast l!ections MS-49 to MS-56 and roll BG-66

or 13()-66-A___ _____ ______________________ 16 Frame FM- 18 or FM- I8--A_______________ ___ 17 Cover BG-70-A______ ______________ __ ___ ____ 18

n. Employment. L · . . lmltatJOns ________________________________ _

" Using organizatiofi8 and normal use_ _____ _____ 20 To assemble theseL ______ _____ ______ ____ ____ 21 Check before operating and cautioll ___ ____ ___ _ Operation in generaL __ __ ___ _______ _________ _ ~ . . ....... nsnllttmg __ _______________ __ ___ __ ___ ___ _

22 23 24

Receiving__ ___ _______________ ____ __ __ ____ _ _ 25

Care and adjugbnenL_______ ________________ 26 Storase-____________________________________ 27

M558597 1

TJ( 11-239 , SIGNAL CORPS

s.mON 111. Detailed functioning of pnrts. hramph

Rudio tr&nsmitter DC-228 or BC-92S-A 'and- •... radio control box BC-2U or BC-235-A_~_·_._ -28

Radio receiver BC-227 or BC-221- A_ _______ __ 29 Circuit elements__ __ ______ __ _________________ 30

IV. Supplementary data. and parts list. Operating currents of radio transmitter BC-228

or BC-228-A__________ ______ __ ___________ 31 Voltages and currents of generator GN-3~_ ____ 32 Dimensions and volume of principal parts_____ 38 Q uantities, weights, and loading of parts on

frame FM- 18 or FM- I8-A_________________ 34 Parts list___________________________________ Sf)

SECTION I

GENERAL DESCRIPTION

P.ra_fIb T)Vti-_________________ ________ _________________________ __ ________ ______ 1

PuKer ___ n ___ n ________ n ____ _ n n n __ n ___ n _ _ n _ __ _ n __ nn n_nn __ 2

Nature of ttalllllDilllion Bnd 'ece, 'lIon ____ n nnnn __ n n ___ n ____ n_____ 8 Dt.tance rangell_____________ ___________________ ______ __________________ .. rTequency .. ~----------------__ ___ ___ _ __ _ ____________ ____ _ __ _ ______ __ ~

a,. nnel!J ___________ __ ______ __ n ____________ u ________________ n____ 6 W eigb t aDII 8J111oo______ _ _ ___ __ _ ___ _ _ __ _ _ ___ _ _ __ _ _ ___ _ ___ _ _ _ __ _ _ __ ____ _ 1 !l'n.DspofL______ ______ _________________ _______________ _______________ 8 Ute______ _ ____ _ _ _ _________ __ _ ____ _ _ _ ___ __ _ ___ _ _ _ ____ __ _ _ ____ _ _ ____ _ ____ 9 ~pooeDt part _____________________ _______ ________________ _________ _

Radlo transmitter BC-228 of 1IC---228-A.. ____________ _______ ___________ _ Radlo recet"eo- BO-221 or BC-221-A.. __ _______ ____________ __________ ___ _ _ Radio oootrol box BC-2SII or BO-23:S-A.. __ ___ __ ___ _____ ___ _____ _______ ___ _ COeDerator ON-35 _________________________ _____________________ _____ ___ _

" " " " " Box BX-12 or BX-l2-A_______________ _____________ __________ ____ __ ____ Ui )Jut f!leCtlOIl8 Ms.-.-49 to Ms-M and rot] TlO- r>6 or BO-t06---A _____ ___ __ __ ____ 16 Frame FM_18 or FM- lS-A.. _______________________________ ___ __ _____ _ CIl'I'er 00-10---,. _ ______________ __ __ __ ______ ____ __ _________ ___________ _ " "

1. Type.- Radio setSCR-203 is a low.power,short-range, medium­frequency, highly-portable transmitting and receiving set, intended primarily for transportation on the back of a pack aniwal,

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RADlO 8ET SCR- 203 TIt 11-839

O-T

2. Powel'.-a. Input.-The power required to operate the trlUlS­

mitter is supplied by a hand gt\nerator and dry batteries, and that required to operate the receiver is supplied by dry batteries.

h. Omput.-The transmitter haa a nominal rating of 7.1\ watts. 3. Nature of transmi88ion and reeeption.- Tbe set transmits

and receives the following: a. Continuous-wave telegraph, hereafter abbreviated as "c. 'IV." h. Tone-modulated, continuous-wave telegraph, hereafter abbrevi­

ated as "tone." c. Voice-modulated, continuous-wave telephone. hereafter abbrevi­

ated as "voice." 4. Datance ranges.- The approximate ranges of this set in miles

are giV1ln in a and b below. (Soo par. 19.) The ranges given in b imply movement on some means of tnlDsport other than a pack animal; for example, it may be expedient to transport the entire set on its frame in a truck. Sinre transmission is accomplished by turn· ing the generator, and since thls tUniing is not practicable while the pack anjmal is in motion, a halt js nl»'S6Rry for transmission when the set is used in mounted BI:lrvlce.

NOft.-Eseept wbere &pI!C!a l perml""lon baa ~n granted by competent authorIty, the mounUnc ot !hIII radio set 1n a veh1cle other than as stated aboye .. prohibited.

c .... ,- ,-CL With the .eton tboo pack animal or on tboo ground. '"

,. , ~ Wltb the aet In movMIlent •• ___ ...... ... ....... W , 3

5. Frequency range.-The set operates in the frequency band from 2,200 to 3,060 kilocycles.

6. Channels.-The numbers of radio channels Rl'ai lable with the frequency separations indicated are shown below. Channels used for one type of signal are not IIvailable for other use. (See par. 19.)

c . ... ,- v_ FrequencY"'pAratlon '" kiloc:ycl ......... ..... ..... 20 '" '" Number ot channcb ................ ______ . ..... .,

" " 7. Weight and apace.-The set weigha 162 pounoh and occupies

18.1 cubic feet of space when completely .rembled. The total load

• 0.., II""" UNIV,~\lTY Of (AllfORNIA --

TK 11-239 ,-<

,

SIGNAL CORPS

on the .nima1, including the pack saddle. is approJ:imate1y 210( pouruU. See eection IV for further details.

8. Tranlport.-The set is mounted on 1\ steel and aluminum frame

TL'I$

non .. 1._ " ...... I'll- I " P ....... I'lI_I8-A ..... IMo ....... PDHIoI ......... ~ ... bat _pIo" • qul<k· .. J.oo .. '7lH' 01 .. _ t ... , ... ",I>< •• to •• ~<I tor lb. paok _<ldlt , .. Ien!ap.

( fig. 1), which in tum i3 clampeJ to II Phillips pack saddle for trans­portlltioll on one pock animal. Mounted 011 this frame, however, the set mlly be transported utherwise, and opernted either on the ground or in the vehicle transporting it, lIS well as on an animal. (800 par. 4.) Figure 2 shows how "arious parts of the set. are located with respect tv the frame and to the animal. (See. pili". 21.)

Rudie rrornmifNr 4 C-226

"-'*'a .. 2.-lRntlo .. of 1>&'" 01 rt4l<> ... IICB_2Oa oa u.. frame ud ... '" .......

• Or'9",.lfrorn UNIVE~\lTY Of CALIfORNIA

,

,

RADIO SET SCR- 2 03

9. Use.-See paragraph 20.

TM 11-239 9-10

10. Component parta.- W hile the Sil,,"lal Corps Genellll Clltalog is controlling in regard to component p'111 8, they are indicat.ed in subsequent parRI,,>Taphs for in tonlllltion. Major c.:omponent p'1T1 s lire covered separately in plIragraphs 11 to 18, inclusive. For II. more comp lete list see section IV.

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,"",u .. J.- ...... n t po ... ' ~'e. M , .dl0 lran ... n , ,, fIC_~2S .• II." 01 ,.d lo _, SCII-20S. TlIo se-:n8_A .. tI.'I._ " ""p' Il, . . . ... . ...... ,w;! blud ,,,. _. 10 lu . be u_, ... M ·b . .... ......... 01 . 1Mo ","utI.

( • Or"}",,, from UNIVE~\lTY Of CALI fORNIA'

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'l'X 11-239 10 SIGNAL CORPS

14 '1,.1 r_U " ..-lDlIlde .... MI. 'fin' 01 radio t'&nllllhte. BC-2~8 0' Bc.-2z&-A. .".-"

caa to 1M u_ Joefl """ .... ""olalno lhe ~Illo.to. Indu<:lon ~LS; ~ below I, 11 lb. ~,to. «II.ID, " p,dlM cs. 10 tile 01>1"" rlcb! ........... tile I1l"lIf ""II '" .1wI uleD,,"- , uolo, 10d"",O>' L7; dl....u, u_. II 10. th. anteDILI. , ..... !"""'. Ll_LI. lJl I IwI e.t~ lo.e. 'lIbl "".,..... ,. the hrlq rolaJ'. ~ .. U .bOWI lhe cIlaaIt -,110'" 01 1_ pUll.

7L-I762 .... C .. ~-y....,t _I -new of .. <110 ~T" BC-HT aDd ,.dlo ..... lroI bu JIC..!U. T1MI

BC-277_A b I~ ..... II tbe BC-2:n • ...". for Iholo'IOWlO, : Tb ....... o<l bl""'D, P"C I. d_ 10 I~ .ntoanl biD-din, _I; 11>0 11"''''01 .~t .. __ to lb. rtp.1 of u.. IO'eOOI _tl. 011_ loSCltE.l8.1:: lhe I"AlAI ....... III lhe ..... Ie. of till panoaIlo. ....w I'IUCQU&'''l'Y COoSTRO L.

( • Or .. , IL" UNIVE~\lTY Of CALIfORNIA

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RADIO err SCN-20! ~ 11-239

11-13

11. Badlo transmitter BC-228 or BC-228-A The transmit­W (figs. 3 and 4) is contained in a. metal case and is mounted on the frame by means of four sponge-rubber cushioned mountings. The circuit elements, including too tubes, are. mounted on the panel and chassis assembly, which is entirely removable from the ca8&. This assembly (fig. 4) is secured to the case by means of tongue and ~roove joints at the bottom and by latches at the wp. Ventilation is provided by a screened opening in tlle bottom of the case and one near the top of the panel. To inspect or replace tubes, it is only nec'l'SSIlry to open the two top latches and to pull the panel forward about 4 inches.

12. Radio receiver BC-227 or BC-227-A The receiver, shown in figuf'8 !i and 6., is contained in a metal case and is mounted on the frame by means of four sponge-rubber cushioned mountings.

TI. */76J '-'0"". lI.-III.Woe _10 Ylew ot .. dlo n«lnr Bc--:?17 or BC--221_ A..

The circuit elements, including the tubes, are mounted on the panel and chlUliis assembly which is entirely remOl'able from the case. This assembly is secured to the case by 11 11'00 snap slides' on the panel.

13. Radlo control box BC-235 or BC-236-A.-The control box, shown in the upper purt of figure 6, is contuined in II metal C&S0

and is mounted on the fl1lme by means Qf two bolts and wing nuts. The circuit elements Ill'll mounted 011 the panel, an interior view <) f which is shown in figu re 7. Thfs paUl'll assembly may be removed from the case by unscrewiug the knob of the trllnsmilt ing key ..... h ich

( 7 Or .. ,,,," fL",

UNIVE~\lTY Of CALIfORNIA •

i'1I[ 11-239! 13-16 81GNAL CORPS

TL -17." """u •• 7.-l1.li<110 oomlrol. boI BC-ltl.::l Oc BC-213-A, Lnt • • Io. "0"\0 .. of po.lIe\" "' blr.

is loeated on the top of the 00';, removing eight screws near the edges o f the panel and lilting 11m assembly.

14. Generator GN-35.-The generator, outlined in figure 2, to­gether with the voltage regulator and ripple- fi lter elements, is con­tained in a metal case and is mounl.ed all the frame by mean.. of a metal strap over the generator.

The two cranks and the crank utensions are removed from thei generator by pulling them out of their slot&.

16. Bolt BX-12 or BX-l2-A._This is s metal OOJ.:,shown cb setl in figure 8 and opened in figure 9, which is mounted on the f rame by means of four heJl;agonal nuta The hingW cover is lleld closed by two push.bUlton !Spring clltche8 protruding through. the h ingW front. The hinged front is held closed by t \\"0 thulllb!lcrews at ita upper

,.·rNJ f"wc.~ S.- B<>I 8X_12 o. BX-12_A, r.-ollt < ...... "1-.1.

comers. The OOJ.: contains comp"rtmente for the batter ies and spare tubes. The terminRl strip (fig. 11) p rovides individulll bind ing posts for the leads of a ll six batteries BA-2. The four batteries BA-23 and the one battery BA-27 are properly tenninated by tIle use of interconnecting wires which are connected to the fonr IIOCkets on the hinged front. T he capacitor CA- I77- A, also mounted on the interior of the hinged front, is a bypass capacitor across the receiver bias battery.

16. Mast sections MS 49 t o MS-56 and roll BG-66 or BG-5~A,--a. A/WJt lIection,.-TIle eight mast sections are made of high • wnsi1e strength steel Mast sect ion MS-t9 fol1Ol:l the top of the

( 8 Or .... fL ... UNIVE~\lTY Of CALI fORNIA

RADIO SET SCR-20S TIll 11-239

16-18

antenna when all aections 11m used; the others follow in the order of their type numbers, and mast section MS-56 plug1' in to the ill8U.lator I N-91, which is the base of the antenna and which is secured to the frame by the bracketa shown in figure 1. Mast section MS-49 tenni. Ilates in a blunt point at the upper end. Mast. sections MS-60 to

rL .11fItI

..... or .. 1I._Bo. 1<:"11:_12 0< 8X_I2-.\, ktt .. k-s 0114 .po,. t~"" In pl .....

:MS-66 are fitted with a. serrated shank and I:J(:rew at one end and thread at tJle other. Ends which are joined in assembling have enamel marks of the same color. The body of each section is enameled black and bears the type number near the lower end. Tbe over-aU length of the as>lembled eight sections is 25 feet 2 inches.

b. Roll.-The roll is made of black canvas duck and holda the eight mast sections in separate compartments. The opening on one end and along the side is closed by a slide fastener.

17. Frame FM--18 or FI![-I~A.-The frame FM- 18 i, shown in figure 1. Cushion pads are provided to hold the transmitter and the reooiver firmly in place. Rawhide leather thongs are knotted through holes in the members of the frame to secure the cover (par. 18) to the f rame. The f rame FU- lS-A differs from the FM- lS in that it has a quick-rfllease type of mounting for the generator and similar straps for fastening the whole fl'llme to the Phillips saddle.

18. Cover BG-70-A.- The cover, made of heavy waterproofed canvas duck, proteets the set when it is mounted on the frame. Ac­cess to the bo:"ll: BX- 12 or nX- l2-A and the generator may be had by opening a slide fRstener immediately over these parts, and 1l(');?,S

to the receiver and We control box may be had by opening two slide

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TItI 11-239 18-19 SIGNAL CORPS

fasteners on the near side. These slide fasteners are protected from moisture and dirt by flaps mending over the fasteners and being held do'lll'Il by snap fasteners. Two pocket.s., one on each side at the front of the cover, are provided for the small parts of the set. The parts which are carried in each of these pockets are indicated in section IV. Two holes, one at the front and one at. the rear of the top of the offside, pennit the roll BG-66 or ~A containing the mast sections to extend through the cover. A hole at the front of t he top, through which the mast eJ:teods, may be cloeed by futoo· iog the small hood attached to the cover.

Sr:cnOy II

EMPLOYMENT PanKft,""

Llmlta tiOTUL._ •• ==. ______ . _____ . _____ . __ .-=====______ 19 IT~l nlJ organTZIIUon8 lind normal u .... _____________ • ___ •• __ _____ 20 '1"0 a!!gelllble the !leL __________ • ____ •• ________ • ___ • ___ •• _______ 21 ('beck before operating Ilnd ClIU(lOD __________ __ _ * 22 Oper.tI .... In geoeraL ___________________ . ___________________ 23

'lTaDllIIllttln'_________________ __________ __ 24 Rece\'rlolJ ___________ _________ •• __ _ _____ .__ ____ z:! Ca", IlDd . dJWltmenL ______________ ...:.______________ _____ 26 Storage.____________________________________________________ 27

19. Limitations.-This set has the usual limitations pasBEmd by any radio set of its power, portability, and frequency range. Tem which discuss these limitations are generally available and are not quoted in this manual. The distance ranges (par. 4) and the channels (par. 6) must be considered approximations which are affected by many factors, the majority of which are not controlled. by the user of the set. Some of th~ which are 90 controlled. are listed below and require the attention of the uller if the set is to be operated. most efl:ectively.

a. Di8tance rang-e.-All other things being equal, maximum effective range is maintained. by-

(1) Frequent inspection of the set II.nd eorreetion of all defects, particula rly in the batteries, tubes, plugs, cords, wires, and binding post contacts.

(2) Using c.w. in preference lo lone and either c.w. or tone in prefer­ence to voice.

(3) Accurate tuning. (4) Locnting the set in a dry place on level or elevated ground,

"voiding all obstructions, either natural or man-mAde, and particularly

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RADIO SIlT SCR-tOa T:M: 11-239 ......

intervening eminences, tall metal structures, power, telephone, and telegraph lines.

b. Ohonn.!h.-The ma:rimum number of operating chllJlnel8 will be made available by-

(1) The action indicated in a(2) and (8) above, particularly that in (2).

(2) Assigning f~uenciea a9 f ar apart as JlO9Sible to nets which must be located close to each other on the ground

20. Using organizations and normal use.--.a. U6ing orglMliMJ­tionI.-Tables of BlUlic Allowances p rescribe the organizations using this set. Generally, it is authorized for US& by the following:

(1) Signal troop of the cavalry division or cavalry corps. (2) Headquarters of the cavalry (horse) brigade, regiment. and

equadron. (8) Headquarters of the cavalry division artillery and battalioll8. b. Normal me.-While the set is capable of operating with various

I other sets, it is most frequently used in-(1) The cavalry division, brigade, and regiment&1 IKIts for com·

munication between and with th096 headquarters, supporting field artillery headquarters, scout cars, and observation airplanes.

(2) The field artillery net of the cavalry division for communication between and with its headquarters, the cavalry equipped with this Sl!t, and observation airplanes.

21. To assemble the aet.-In mounting the parts on the frame, avoid the use of tools on latches, slides, binding posts, nuts, and plugs whuever possihle. Before connecting plugs to sockets, inspect the attachment of the cords to the plugs. If tile cord clamp appears 10000, tighten the small knurled locking ring at the base of the plug by turn­ing it COU1Itl!f1'Clockwiu. In connecting the plugs to the sockets, place the Rrrow stamped on the plug opposite the arrow stamped on the socket, thrust the plug into the socket, and lock it by turning the large knurled band of the plug dookwi&e and tightening it in the socket. Figure 10 shows the ertel .1al cording and wiring of the set.

a. Trammitter.-(I) Face the panel, tum the ends of thetwolateb .... toward each other, pull the top of the panel forward, and hold it OpeD

with one hand. (2) See that the caSEl contains nothing except the panel and chassis

assembly shown in figure '" Rnd B. circuit diagram pasted on the rear inside wall. If the set is being placed in service for the first time or after extended storage, lubricate the worm screw of the ANT. COUP­J.lNO control with a small amount of petroleum jelly.

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,'l'ld: 11-239 .. SIGNAL CORPS

(8) Ineert a tube VT-60 in the center socket marked MOD VT-60, and a tube VT-26 in each of the side sockets marked PA VT-26 Illld MOVT-25. Closesnd latch the panel.

(4) Remove the four wing nuts and lock washers from the mount­ings. Place the transmitter on the frame in the position indicated in figure2, being sure that its twooords CD-202 and CD-S!16 are placed untwisted between the back of the cas6 and the two horizontal mem­bers of the frame. Secure the transmitter by replacing the washers and wing nuts.

(5) Using a suitable length of wire W-l24 provided with the set, connect the OND binding post of the transmitter to the nnmarked, binding post on the offside rear member of the frame.

b. Rectiver.-(l) Face the panel, release the three snap slides on • it, raise the slide opening at the bottom of the case, grasp the two

handJee at the ends of the panel, and lift the w .mbly shown in figure 6 out of the case If this assembly is removed at any time after the

""----.­Pw:JU'Q 10.-lI.adlo ott SClI.·203, top Y\eW or e_1 ",,!'dlo,..,4 ~

cords are connected, always disconnect the plugs first to avoid shorting the receiver batteries.

(2) See that the case contains nothing ucept a circuit diagram pasted on the rear inside wall.

(3) Install a lamp LM-31 in its socket just below the meter. Do this by putting the forefinger of each hand around the meter, holding the bulb between them and turning it into ita socket a little: at a time.

12 0.." II""" UNIV,~\lTY Of (AllfORNIA

RADro SET SCR-203 TM 11-239

" -(4) Inllert a tube VT -24 in each of the five sockets. Replace the

assembly and secure it to the case. (5) Remove the four wing nuts and lock washers f rom the

mountings. Place the receiver on the frame in its proper position, being sure that its two cords CD-207 and CD-211 are placed un· twisted between the back of the case and the bottom horizontal member of the frame. Secure the receiver by replacing the washers and wing nutA

(6) Using a suitable length of wire W-I24, connect the GND binding post of the receiver to the unmarked binding post on the near·side lower front member of the frame.

c. Oontrol bO:ll.-(I) Remove the two wing nuts and lock washe1'S. (2) Place the control bol[ on the frame in its proper position so

that the cord C!)....2U of the receiver and the cord CD-216 of the transmitter are untwisted and between the control bol[ and the upper horizontal member of the frame, and that cords CD-207, CD-216, and CD-lSI are between the control box and the receiver. In bringing cord CD-216 from the oft' to the near side, run it under the top members of the frame. Replace the washers and wing nuts.

(3) Connect the plug Plrll6 on cord CD-2m to the socket on the control box marked REe.

(4) Connect the plug' PL-90 on cord CD-216 to the socket on tha control box marked TRANS.

(~) Using suitable lengths of wire W- 124, conned the receiver binding post marked ANT. to the control box binding post marked REC., and connect the transmitter binding post marked ANT. to the control bol[ binding post marked TRANS., running the latter wire between the two receptacles on top of the framll provided for the generator and for the bol[ BX- 12.

d. Battery b00.-Test all batteries before installing them as indi­cated below, and do not install any the voltage of which is less than that given in paragraph 2k If, after the assembly action indi­cated below is completed, replacement of batreries BA-2 or BA-27 is necessary, disconnect all plugs Crom the box and remove the box from the frame beforo atrempting to open the hingOO front.

(1) Face the front of the box and open the hinged cover and front. Do not «Ue tlu metal &pace collar on each. of the two thwmb­."""'.

(2) Place three batteries BA-2 in the right compartment with their red leads nearest the terminal strip Ilnd connect them a.s indicated in figure 11, bringing the leads wu:kr the wminal strip.

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TJ[ 11-239 .. SIGN",-L CORPS

(8) Place three more batteries BA-2 on top of the first three with their reel leads also nearest the terminal strip, and connect tbem a8 indicated in figure 11, bringine the leads over the terminal .trip.

(4) Connect the - 41h and the + terminals of I\. battery BA-27 to the two wires looated below the terminal strip and marked - 40.6V II..IId +4.6V, respectively. Press this battery into the space between the right end of the box and the spring clip.

W'\ .. "". 12._Boz BX- U. batterT SA-2& <"<>nnO!C1toDO.

(15) Place four batteries BA-23 in the middle compartment and connect them to the wires marked + U;V and - UiV as indicated in figure 12. Tighten the wing nut of the compartment to bold these batteries firmly in place.

(6) With their bases up, place three tubes VT-24 in the small felt pockets, one tube VT-W in the larg6 rear pocket, and one tube VT- 25 in the remaining pPCket of tbe left compartment. Wrap the spare lamp in .. small piece of paper a.nd plaCE! it in one of the pockets.

(7) Close the hinged front, tighten the thumbscrews with their collars in place, and close the hinged cover.

(8) Remove tbe four hexagonal nuts and washers from the wp of the frame, and place the box on the frame in its proper position, being SIll'e that the wire W-124 from the u8 Dsmitter w the control box is .. 0.., II"""

UNIV,~\lTY Of (AllfORNIA

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lL\DIO SCT i5CR-20ll TM: 11-239 ..

plaoed oot .. oon the box and the receptacle for the generator on top of the fram\\. Replace the w9.8hers and nut&

(9) Connect the plug PL-97 on cord CD-202 to the socket of box BX-12 marked PL-Vl TRANS., bringing the cord under the top mem­bers of the frame.

(10) Connect the plug PL-lOO on cord CD-131 to the socket of box BX-12 marked PL-loo CONTROL BOX.

(11) Connect the plug PL-89 on cord CD-211 to the socket of box BX- 12 muked PL-89 REC.

~. O~nemtor.-(l) Removethewingnutfrom themetal strap at the front of the near side of the frame FM- l8, or open the releaoo catch on the FM-l8-A, and place the generator on the frame with its socket side next to the battery box. Secure th~ gIlnerator to the frame by replacing the metal strap and wing nut, or closing the releaS6 catch.

(2)) Connect the plug PL-88 on cord CD--0O3 to the socket of the box BX-12 marked PL-88 GEN., and the other plug on this cord to the socket of the generator.

(8) Insert the two crank extensions in the ends of the generator shaft, and the two cranks in the ends of the crank extensions. Do run turn. tM generator tcithout reudi1l{/ parwpaph fl!.

f. Antenna.-The assembly of the mast with all eight mast sections .... ill give the set its maximum range. H owever, it is sometimes advis­able to use fewer mRSt sections when only short. diStances are to be covered; the reduced radiation minimizes interference with nearby . elations operating in other nets. Furthermore, when the set is on a pack animal, the use of the full mast is often impracticable, especially if the animal is res~leflS or if the wind is of appre;iable intensity. If communication with a short mast is not satisfactory under these con­ditions, remove the set from the animal, place it on the ground, and erect the full mast., with guys, as described in (2) below.

(1) When the get is to be used in mounted service, a . . mble the aerial by screwing together the desired number of mast. sections, be­ginning with the LJttom mast section :rotS-56, and then push the end of the latter into the supporting insulator I N-9I.

(2) If the set is to be used on theground wi th theeight-section mast, guy the antenna. To attach the guys, slip the collar of the guy GY-ll over the lower end of mast section MS-sa with the points of the hooks toward the base of the mast, close tile collar and secure it by attaching the hook of the guy GY- 12 with its point toward the base of the mast.

(8) With the mast lying on the ground, place the guy lines parallel to it and the ends of the lines near the base of the mast. Raise the mnt

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TK 11 239 ..... aIGNAL CORPS

in one continuous movement until it is vertical and slip it into the insulator IN-91.

(4) GUY .the mast by SUlking the linllll at three points equidistant from tb& be.se of the mast and· spaced 12()0 apart. Guard against ere .rive bending of the mast in raising and guying it.

(0:) For a ground, run a wire from one of the screws or one of the binding posts of the frame to a stake driven in the ground. Wherever possible, drive the stake into the ground near the roots of a tree, shrub, or cactus, below ground level.

(8) Connect the terminal of the insulator IN-91 to the binding post en the control box marked ANT. by means of the short rubber-c:overed cord provided for this purpoae.

g. O(>V",".-In oovering or uncovering the set with theoover, IIIlII that the top slide fastener is open. It should be eloeed wben tying and untying the leather thongs. If the roll BG--66 is esqembled on the frame as shown in figure 2, remove it before removing the cover, and attach it. after putting on the cover. Remove the front of the cover before the rest and replace it last.

h. Rolt-Keep mast sections not in use in tbe roU and the roll attached to the frame as shown in figure 2.

i. Other pdrl",.-Keep all parts not in 1llIe in their proper pockets of the cover.

;. Supporl.-II the UOO'Dbled set is to be kept on the ground for an extended period. of time, improvise a support for the loaded frame which will prevent undue Bpl . 1 ding of ilJi sides. It time will. not permit this, at 10llSt tie the thongs on opposite sides together for the same purpose.

22. Check before operating and c&utlon.--a. GeneraL-Before operating the set, check the equipment to determine that the tubes are of the correct types and are finnly seated in their sockets, that the batterillll are of sufficient voltage as indicated in paragraph 26a, that the plugs are properly connected to their eook:ets, and that ths wire connections ll.r& correct and Ilttached to their t.enn.inal!O. 800 that all nuts securing the parts to the frame are tight, that all parts ar& in placs, and that ths snap slides and latches are claml.

Caution: This set operates at high voltages which are dangerous to life. Therefore, keep away 1'l'(WTI, high 'Coltagf) kad.6 at an nma and do flOt change. tube. 01' make adjtutmcn.tl i'Mkk the ,et ICAiltJ tAa gMlNat<Jr if being turnecl.

o. GenHrator oh.eck.-Wben the generator is adjusted for 8 volta on the low volt1£e Bide, the high voltage will be approximately sro

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RADIO UT SCIHJ08 TJ[ ll-a39

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l'olt& These adjustments are made by the mfUlulaetttrer or at the depot before the generator is issued. Howel'er, always check a generator before taking it into the field and make any nee ry adjustment of the voltsge regulator. (See ptu". 2iIb).

2S. Operation in general.---a. lnt61"f~.-(l) ; Interference with reception may take on various t'Ol'lllll and is caused by' either atmospheric electrical disturb!lIlC88 or electrical disturbances pro­duced by the operation of electrical equipment, including ail types ()f machinery, vacuum tubes, power, and communication lines, radio transmitters and receivers. Electrical disturbances caused by at.­Illospheric conditions am tiually registered in the headset as a series of irregu1arcrashes, hissing, and frying sounds. This cannot be elim­inated. Communication can be carried on only when the signal strength is above the noise level of the interference.

(2) Rotating machinery, like caterpiilar.dril'en tanks, may ca\llllll

considerable trouble, particularly if the communication equipment is defective in any respect.. This may be indicated by a steady or irregular hum depending on conditions. This trouble should be corrected at the source if possible.

(3) Power lines may give rise to interference directly be;:all"9 of the electromagnetic field produced by the cun-ents in the lines, and indirectly because of the elfect of the conductors and their position with respect to the receiver antenna. The direct eJfect is npparent un all frequencies but is particularly noticeable on the bigbet" ranges. As it is not known how to eliminate this form ot' interference, 0pera­

tion in the immediate vicinity of power lines must be avoided. when­ever possihle. The indirect effect may be noticeable when tral'eling parallel or nearly 90 to a power or communication liM. It is appAl'­ent in the receiver headset as a. periodic increase and decrease of iOlgnal intensity. This phenomenon appears to be caused by the action of the conductors as parasitic antenna producing !;tanding waves, whenever the distance between the conductors nnd the receiver antenna bears certain relations to the wave length.

(4) DischArge acl"OSl:l defective insulators on power lines will gil'e rise to a series of irregular crackles or hums. Clicks, either regular or irregular, may often be traced to switch gear, thermostatic devices, and sign D~rs in the immediate vicinity, or to defective resiston and capacitors in the receiver or power supply itself.

(6) Heterodyning of the carrier waves of two or more stations operating on nearly the sam!) frequency or 06C'iIIe tiona at' the re-

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T:M: 11 239 2') 2' BtONAL CORPS

cei.er itself will produoe whistles and squeals of varying pitth d&­pending upon the difi'erenee in frequencies.

(6) The above-mentioned forms of interference and others may be identi6ed after Borne experience. As correction of electrical condi­tions not in the radio set or power supply itself is usually not feasible, the only way to reduce or eliminate the noise is to operate at another location.

o. Net operation.-If net operation is desired, each set must be accurately tuned to the same frequency. This may best be accom­plished with the aid of II. frequency meter. All .et. 1Cithin OM net mull be tuned WIder wubltantially tlu .1Ime cmaditiOM. The posi­t ion and length of antenna, the temperature, and the battery ter­minal voltage must all be fairly uniform if succ u' ful operation is to be ezpected. A void tuning in the immediate vicinity of buildings or metal structures. Do not tune a set in a heated garage, fOf" enmple, and expect it to be on frequency when taken into the field under colder weather conditions.

c. N etlwd. 01 operatio-n.-Always operate the transmitter with the antenna circuit tuned. This is particularly important in net operation in order to maintain tha correct frequency. Being broad. tone transmission is well adapted to net operation but produces more interference to nearby radio sets than c.w. transmission. Voice trans­mission produces more interference than tone traDfllTljssion. (~ par. 19.)

24. Transmitting.--a. O;;mt;roh (figs. 8 and 1i).-Transmi9Bion is accomplished or controlled by the foUowing:

(1) The generator .. (2) On the control box (a) The changeover switch marked TRANS. OFF REO. (') The lmy. (8) On the transmitter or connected to it-(a) The antenna coupling control marked ANT. COUPLING and

Jocated near the upper left comer of the panel. An arrow point­ing counterclockwise is marked OUT and clockwise is marked. IN.

(b , The antenna tuning control marked ANT. TUNING and lo­cated immediately below the antenna coupling control «a) above). An arrow on the knob together with the mark MIN. on the left and MAX. on the right of the knob indicates the limits of tuning.

(e) The antenna current meter marked AMPERES R. F. with a scale from 0 to 1.5 amperes and located just below the InIADD. tun­ingoontrol (0) above),

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llAmo SET SCR-203 TIll[ 11-239 ..

(d) The transmitter switch marked TONE C.W. VOICE and lo­cated just to the right of the antenna current meter «c) above).

(e) The key jack marked KEY located just belo .... the transmitter switch «d) above) and the key and cord when connected thereto.

(I) The plate current meter located near the center of the panel and marked TOTAL PLATE CURRENT with a scale from 0 to 200 mill iamperes.

(9') The neutrallzing capacitor control marked NEUT. CONDo and located to the right of the transmitter switch «d) above). This control is adjusted at the factory, and further adjustment in the field is not ne<:f.'SSIlry.

{II) The 05(!i llator control marked OSCILLATOR at the lower right corner of the panel with a pointer and scale from 0 to 10 in tenths.

(i) The microphone jack marked MICROPHONE, located jll!lt to the left of the oscillator control «A) above), and the microphone pnd oord when connected thereto.

b. Procedtlre.-Regardle:ss of whether transmission is to be Co w. tone, or voice, f ollow initially the procedure indicated in (1) below:

(1) 17(Y1' c. W., to'M, (YI'tloice.- (a) Read paragraph 22. (b) Tum the changeover switch of the control box to TRANS. ( c) Tum the tra.nsmi t ler switch to C. W. (d) Set the OSCILLATOR pointer at the setting ooliooponding

to the frequency at which it is desired to tra.nsmit, obtaining this setting from the tabulation of frequencies and settings mounted on the upper right of ~ panel. If the desired fn!queney is betwl!en IIny t .... o frequencies t..'\bubtcd, interpolate the value of this setting.

(e) Rotate the ANT. COUPLING control counterclockwise in the direction of OUT as far as possible .... ithout forci ng. Forcing this control is likely to binu and break fhe fragile isolllntite mountings. There sre about 22 turns from the IN to the OUT limits. Thu. con· trol causes the inner inductor Ll to slide in and out of the outer fi:a:ed inductor 1..2.

(I) Connect. the OOnninals of the cord CD-201 to the key J..46, lind the plug of this cord to the jack marked KEY. While th6 key on the control box may be used for transmission, key J-4~ is more convenient at this time. If II longer cord is needed, use t he extension cord CD-l99 a lso. The key is mounted on II large open clasp which fits around the opera.tor's leg just above the knee.

(g) Turn the generntor from W to 70 revolutions per minua, and during the operations indicated below in (A) to (k), indusive, close and open the key inkrmiUenlly, but do not permit the TOTAL

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. TIl[ 11 239 .. 8IONAL CORPS

PLATE CURRENT reading to exceed 100 milliamperes. VrJuea ('xceeding this will 9I:'riously overload the gllnerator.

(h ) Operate the ANT. TUNING control until a maximum read­ing is obtained on the antenna current meter. If no reading is obtained, rotate the ANT. COUPLING knob clockwise OM or two turns Rnd repeat until a reading is obtained at !lOme point of the ANT. TUNING operation.

(i) Watch the TOTAL PLATE CURRENT reading, and if it is less than 100 milliamperes rotate the ANT. COUPLING control clockwise until about that reading is obtained, but do not ezooed it.

(j) Operate the ANT. TUNING control so as to obtain a maxi­mum antenna cummt as in (h) above. If the TOTAL PLATE CuRRENT ellceed, 100 milliamperes., rotate the ANT. COUPLING counterclockwise in small steps to reduce it to that value.

(k) Continue (h), (i), and (j) above until the antenna current is about .6 ampere, with a total plate current not in e:loet'l8 of 100 milliamperes. It will be noted that the ANT. COUPLING and ANT. TUNING react on each other. When a final adjustment is reached, varia.tion of the latter should reduce both the antenna and total plate currents. This is an ideal condition which will not. always be obtainable in: practice.

(2) For ttmt .-Hilving completed the procedure directed in (1) above-

(a) Stop the turning of the generator. (b) Turn the transmitter Bwitch to TONE. (e) Continue as dil'6C~ above in (1) (g) to (k), inclUlJiTe, except

keep the total plate current at or below 125 milliamperee instead of 100. If it is found impopible to keep this current at or below 125 milliamperes without a material change in the !letting of the ANT. COUPLING C(lntrol obtained in (1) above, check the voltage and connections of th& transmitter biasing batteries. The96 am the two batteries BA- 2 nearest the middle of the box BX-12. Weak or improperly C(lnnected biasing batteries will seriously overlOAd the generator and may caU96 serious damage to the set when tone or voice '>perated.

(3) For 't'Mce.-Ha.ving completed the procedure directed in (1) above-

(a) Stop the turning of the generator. (b) Tum the transmitterswitcll to VOICE. (0) Disconnect the key J-45 from its jack. (d) Connect the plug PL-6B of the microphone T-17 to the jd

marked MICROPHONE.

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RADIO SET SCR-203

TlI[ 11-239 SI' Slli

(tI) Contimre 1\8 in (2) (el above except speak into the microphone at a normal tone while operating the button on the microphone intermittently.

26. Beceiving.--a. Ormtrou (fig. ti).-Reception is accomplished or controlled by the following :

(1) The cbangoover switch on the control box marked TRANS. OFF REC.

(2) On the receiver or connected to it.--(a) The filament switch marked O~ OFF and located near the

upper center of the panel. (0) The fillllllent rheostat adjusted by means of the unmarked

octagonal knob just to the left of the filament switch. (e) The meter located just to the right of the filament Hwitch

and marked VOLTS DC with two scales from 0 to 140 volta and Ow 8.5 volta.

(d) The tuning control located just below the meter and consist­ing of an unmarked octagonal knob and, visible through a circular window, a dial graduated from 0 to 100 operated by the knob and illuminated by a lamp.

(e) The regeneration control located at the lower right comllr and consisting of a knob marked REGENERATION and a pointer beneath. the knob operated by the knob.

U) Two jAcks at the right lower edge of the panel marked PHONES and the headset and cord when connected to either one.

b. Procedu:re.-( t) Press on the pin near the botwm of the meter and read the upper scale of the meter. The reading should be be­tween 90 and 72 volts; if less than 72, replace any of the four bat­teries BA- 2 nearest the right end of the box BX-12 whose voltage is less than 18 volts.

(2) Tum the changeover switch of the control box to REC. (8) Turn the filament switch to ON and read the lower 9C&le of

the meter. • .. __ .. __ lp should l ight, illuminating the tuning dial. (4) If the meter reading is less than 1.1 "olts indicated by tila

red line on this scale, turn the filament rheostat clockwise until the noodle reaches that line. If a voltage of .96 volt cannot be obtained in this manner, replace MY of the four batteries BA-28 in the box BX-12 whose voltage is less than 1.2 volts.

(6) Put on Md adjust a headset P- 18 and insert its plug PL-M in one of the jacks. If a 10ng\1r cord is needed, use the extension cord CD-loo also. A rustling sound should be heard; if not, use another headset alld check the assembly of ~ equipment and the procedure above.

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SIGNAL CORPS

(6) By operating the tuning control, set the dial at the setting conooponding to the fn.quency. of the expected incoming signal, 0b­taining this setting from the tabulation of frequencies and settings . mounted on the lower left of the panel. .

(7) Turn the regl!nerntion COntl"9l knob in the direction of the arrow (clockwise) until the 9('t begins to oscillate lUI evidenced by .. plop sound in the headset. Thereafter, operate th is control and the tuning control wgether until the desired. signal is receh·ed. For c.w. the fonner must be just beyond the point of oscillation, and for wne and voice, below this point. As the dial readings are decreased, the regeneration must be increased to obtain oscillation.

26. Care and adjuatment.-a. GeMrol.- The units of this set are designed for field use and with reasonable core in handling and ope.rnting will give satisfactory service. K eep the equipment clean, and check all mechanical fittings periodically to see that screws and nuts are tight and in place. Loose and broken connections are the sources of most operating troubles. The set must be inspected, regu· larly or interrupted eervice will result. If open leads are suspected, check the circuit in question, using a battery and small voltmeter or headset. Tubes will gradually lose their efficiency and should be interchanged with tubes of J..'1l0"l'l"ll value. Tubes shoul,' J6 tested wi th the testeet I-M-A. All butteries in the hoI: BX-12 sr <lId be checked under lond after SIlveral minutes of operation. Any ell the voltage of which has droppetl below II. satisfactory level sh, .ld be replaced. I n general a perceptible increnae in noise level will ndicate "l'rhen a battery is at the end of its useful life. The following voltages may be considered. as the minimum for satisfactory perfonnance: BA-23,1.2; BA-27, 3.6; BA- 2, 18.0.

b. Generator.-(l) l 114pectWn.-The generator housing should be opened at intervals and the commutator, brushes, voltage regulator, choke coil, capacitor, and bearings examined. The commutator should besmooth and entircly free from any black spots or disooloration. The brushes must seat properly 8.nd press finnly against the commutator. Carbon dust should be removed.

(2) Oom.mutator.-If the commutator is black, rough, or pitted, U96 8. piece of dry cloth free. from lint and try to rub the black spots oft', but do Mt use emery cloth. Only as 8. last resort, it should be resurfaced by running the machine and holding a fine grade of sandpaper (No. 000 or finer) against the surface until it. is entirely smooth.

(3) B7"WIM8.-If tbe brushes have worn down or are broken, chipped, or defective in any way 1hey !'.hould be replaced. In seating

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RADIO SET SCR-20a: Tlt 11-239 ..

new brushes, dip a piece of sandpaper, cutting Bide out, between the brush Bnd the oommutawr, and while turning the machine allow the brush to be prr -" :d .aga.inst the sandpaper until it is properly seated. Use a cloth saturated with gasoline or carbon tetrachloride to wipe oft' oil and grease. Never lubricate the ooDlDlutaoor with oil or grease. If it is smooth, if the mica is properly under cut, and the brushes properly fitted, no sparking should occur at the contact between the brushes and oommutator.

(4) Voltage re;uuuor.-If the voltage regulator is suspected of giving trouble, it may be tested by disconnecting it and the open field coil lead CQnnected to the choke-eoil tennmal which is connected to the positive brush of the low voltflge side. If the choke coil or capacitor is suspected, it should likewise be disconnected and tested; if defedive, replace it.

(.5) Voltage adjudment.-{a) If a separate voltmeteJ:' is not avail­able to check the voltages of the generator, only 0. rougb cheek of its operation is possible. With the generator disconnected from the cord CD-203, it should turn with little or no resistance at speeds above 60 revolutions per minute. Below 40 revolutions per minute th~ is an appreciable resistance to turning due to the fact that the voltage regulawr does not operate below that speed. If the generator turns easily at all speeds or hard at all speeds., it is an indication that the voltage regulator is out of adjustment or that the generator is out of adjustment. See also paragraph 24b(2) for a. possible cause of ho.rd turning when the generator is connected to the set.

(6) If it a.ppears that the ~nerawr is not delivering current at the proper voltages and a separate voluneter is available, di800nnect the cord CD-203 from the generator and measure its volt.age$ while turn. ing itatSO to 70 revolutions per minute. The voltages should be from 8 to 8.26 and f rom 326 to S66 NIts, and if they are not about these values adjust the voltages as indicated below. Voltages higher than 8 and 360 volts will reduoe the life of the tral1llmitter tubes.

(0) Remove the four screws from the top of the generlltor housing, the two screws from the top of the projection on the right-hand Bide of the housing and litt olt the cover plate.

(tl) Remove gage TL-l27 from the inside of tOO cover plate. (e) F igure 13 shows a side view of the volt~ regulator the wp of

which can be seen inside the housing. Loosen both locking screws L. (f) Back: oft screw B so that the %~.inch end of the gage may be.

inserted between the core and the armature. Screw up on the screw A until the armatUf&ow-core clearanCIl is adjusted to %4 inch.

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(g-) LeeTe A in place. Insert the .00000inch end of the gage be­tween the armature contact and B, and screw up B for an easy slip fit. Be. careful not to make this 6t tight enough to damage the gage. 7ighten the locking screws L.

(h) If the voltages are too low, tighten the screw a by turning it cloclcwise; if too high, loosen this IICl"IlW. This adjustment is very critical &nd lllust be carefully made.

,

'(-1 Check the adjustment. A wobbly \'oltage indicates that the .. rmature travel is too greal; failure to build up voltage, evidenced by ea.sy turning at all speeds, indicates that the armature tral'ei is too small; hard turning at all speeds indicates that the armature is touching the core and the A ecrew.

(j) Replace Ind secure the gage and the cover plate. (6) LvbTirotion..-Lubricate bearings and gears with New York

and New J ersey lubricant F- 9'.M or, if that i8 not available, with petroleum jelly. At regular inten'alsclean theee parts thoroughly with carbon tetrachloride or gasoline lind then lubricate Ihem. (]auti01l:

Do noe 'fJMk bearingl beeall96 too much grea.se will cause eJ:c-nive hellt Ilnd also o,·erHo\\· onto the commutator. This type of bearing requires very liule lubrication, the principal purpose of the gttase being to protect the bearing against rust and corrosion. All bearings and the gears on one side of tIle geIM!l"1Itor case Ilre aocpmible by reo moving the gearcaseon the right of the housing, whicb is 8eCUred with five machine ecrews. T he bearings on the opposi te side of the gen. erator case are Ilocesslble by removing the two small plates, each se.­cured with two machine screws.

2 7 . 8 tora.ge.-. If the set is to remain out of service for more than a few days, proceed as follows: '

(1) Remove all batteries from the box BX-12, and all tubes and the lamp from the transmitter Ilnd receiver.

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RADIO SET SCR-203 T1I!I 11-239 ,

" .... (2) Blowout the inside and outside of all parts with an air hose

or bellows to remove all loose d irt. (8) Cover the ends of the mast sections with petroleum jelly .

. b. If the-set is to remain out of servi~ for more than a month, in addition to the above-

(1) Wash the generator bearings with carbon tetrachloride or gasoline and pack them with petroleum jelly_ When the generator is again put into service, wash the bearings again with carbon tetra­chloride and cover them lightly with petroleum jelly 118 indicated in paragraph 26b (6).

(2) Remove all parts from the frame and wrap each individually with a heavy grade of manila paper. Pack tubes and other small parts 60 as to avoid damage to them in storage. -

SrcnOli III

DETAILED FUNCI'IONINO OF PARTS

h_" Radio tr&D8m!tll!r BC-228 Or BO-22S-A Ind radio colltrol hoI BC-231I

or BC-2a5-A__ ___ ____ _____ __ _______________ ____________________ ____ 28 Rad!o rece\"l!r BC-227 Or BC-227-A ______ ___________ _ ___ _____ __ ______ 29 CI ~ul t elemen ta_ ___ _ _ ____ ___ _ _ _ _ __ ___ __ ___ _ ___ _ _ __ __ _ __ ___ _ _ _ ____ _ _____ SO

28. Radio transmitter BC-228 or BC-228 A and radio con­trol boz BC-235 or BC-235-A.-a. Circuit.-The transmitter is of the master-oscillator, power-amplifier type. It utilizes a tube VT-25 as mllSter oscillator, a tube VT-ro as modulawr, and another tube VT- 25 lI.8 powl!r amplifier. (See fig. 14.)

b. M(JJIter 08cillator.-Th is is a tuned-plate oscillator, the principal elements of which are the tube VT-25, transformer 4, and capacitors C. and CII and CI • L" has two windings, one in the plate circuit, and the other in the grid circuit.. The mutual inductance between these two windings provides the grid-e:z:citation voltage required to produce oscillation. C. , CI, and C. together provide the requisite capacitance to determine the frequency band. C. is a fi:z:ed mica capacitor, CI is the variable tuning capacitor (represented on the front panel by the dial marked OSCILLATOR ), and C. is the adjusting capacitor which enables accurate calibration of the tuning capaciwr CI • R. is the biasing resistor and C I and Cn are by­pass capacitors. Variable Callacitor C. is adjusted by means of a screw driver inserted through a hole in the lower part of the right sida of the box containing the BC-228 or B0-22!3 A. This hole is normally closed by a screw plug to excJude dirt.

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8tONAL CORPS

e. P(Jt(Jer ampli~.-The circuit elements of the power amplifier are the tube VT- 2:i, r.' . choke coil 1..., reeiston It. and Ro, and a­paciton c., C" and C.- The radio.fnqueney voltage of the master oecillator is impr qd on the grid of the 'power ~plifie.r through Or

,

K_U .

Coils L , and 1.., comprising the antenna coupling t ransformer, eerve to transfer the radio f ro(jueucy energy from the power amplifier to the antenna circuit. Coil L, and capacitor C, are the tuning cle­menU:! of the antenna circuit. c,. is the capacitor marked ANT.

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UNIVE~\lTY Of CALI fORNIA

RADIO SET SCR-20S TJ[ 11-23.9 ..

TUNING on the tront of the set. L. ill tlle radio frequency choke tooil whicb serveIJ to prevent radio f requency currents from Bowing through R. and R. and enter ing the bia!! supply lead, and thus main· tains the radio frequency excitation voltage between the grid and

filament. It, and It. ure g.-id·biasing resistol"ll; C. and C. ue by"a&;! capacitoN.

d. Modtdatcr.-11Ie circuit elements of the modulator are u.e tube VT- 60, transfonner T "coila L, and 1..0, ruinol"!l R. and R" and capaci.

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TK 11-239 .. SIGNAL CORPS

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tors c" and Ot.. The interrupter H t , capacitors C. and ~ and rraill. tor R.. all in the control box, are a part of the input circuit of the modulator. The microphone T-17 is also & part of the input circuit pel is connected by meeDS of jack J.. The transformer T. ,. ue

!: ~ , i:!

• , •

I •

l , , i 1 1 , , • ~ ~ • • , • I

" • , !

to increase the audio frequency voltage of the interrupter or micro­phone applied to the grid of the tube. The interrupter produces an audio-frequency note of l ,sro to 1,6M cycles when connected as shown in figure 14 with the magnet coil in series with the half

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RADIO SET SCR-303 T1II[ il-l39 ..

of the carbon button adjacent to it. L. is the modulation reactor which acts to maintain the constant current required in this (Heising) system of modulation. L. is the choke coil which serves to reduce radio-frequency currents in the plate circuit of the tube to 8. minimum. R, acts to isolate or filter the grid·biaa cirouit

~ , , ~

; I • ! -• • • -I

•

~ • , , j • 0

I i , • I. • -, !

of the modulator tube. The total grid bias is the sum of the voltage drop across the resistor R. and the two 22¥.!-vo!t batteries. R. serves as a constant load impedance of the transformer T, and tends to prevent distortion. C, and en are bypass capacitors.

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TJ[ 11-239 .. SIGNAL CORP!!

-

e. a.VI. troMmiuion (6gs. 14 and 15).-The masUr oscillator and power amplifier operate to transmit c.w. signals when the key is depw ed, closing the low-voltage circuit to the relay RL, which in turn clO!leS the pla.te cireuit of the amplifier. The modulator does ,not operate, as the filament of this tuoo is di9COnnected by

i:! ... , • ~

; I ! ! -! • , J • 1 -, , ! 0 • -• , • , I --, ~

the selecklr switch. CapacitQfS Cli and C .. (fig. 14) serve to redues liparking IICro.;s the contact points of the relay Ilnd key clicks ill the transmission.

f. Tone trammi4fiqn (figs. 14 lind 16).- All tubes operate on tone transmission. The contact on the selector switch closes the filament

30 0.., II""" . UNIV,~\lTY Of (AllfORNIA

RADIO SET SCR-208

TM: 11--239 8S at

cl1'Cl1it of the modula.wr tube. The key serves to cl0S6 the inter­rupter-transformer cin:uit and the circuit through the coil of rela.y RL, which in turn closes the plata circuit of the modulator and amplifier tubes. Resistor R, in the control box serves to provide the proper operating l'olta.ge for the interrupter. Capacitors C, and C. in the control box serve to impress the audio-frequency voltage of the interrupter on the hea.dset through the receiver jack (side tone), and also across the primary of transformer T t •

g. V Dice tran.rmi.!l"um. (figs. 14 and 17) .-All tubes operate on voice transmission. The selector switch connects the eonta.ct points of the relay, thus closing the plate circuit of the modulator and amplifier tubes. It also connects the microphone T- 17 in series with the pri­mary of transformer T t and the resistor Ro. The microphone i!J connected by means of jack J.. The resistAlr R. serves to reduce the generator low voltage to the proper value for the micropbone.

29, Radio receiver BC-227 or BC-227-A (fig. 14).-Tbe re­oeiver cireuit comprises two stages of radio-frequency ampl ification, Ii. regenerative detector, and two stages of audio-frequency amplification. 'lubes VT-24 are used in all stages. Reception of all types of signals , over the frequency range of 2,200 to 3,060 kilocycles is a.va.ila.bla. All stages are inductively coupled. L t , L., and L. serve as interstage r.f. transformers, a.nd C" e .. and C, serve IL5 tuning capacitors for them. T, and T. serve as the audio-frequency transformers to couple the detector, first, and second audio.frequency amplifier stages. T. is the output transfonner. C., C., and e. are alining capacitors. These are adjusted aoourately at the factory and will rarely require reSEtting. CIt is a grid-eoupling capacitor. e. and e,o serve to couple the plate of the detector to the grid, thus providing regen­eration. e,o is controlled from the front of the panel by the knob marked REGENERATION. e. is a mid~t variable capacitor which is adjusted by a screw driver through a hole in the lower left chassis bracket (as the 86t is viewed from the renr). This may require adjustment if a new detector tube is installed. Set. the tuning dial to 100, and the regeneration pointer about an inch above the extreme left position. With Co at minimum capacitance (plates entirely unmeshed), start turning it up slowly until the rush.ing noise and "plop" indicative of regeneration is heard in the earphones; leave it in that position. A!J the dilll is turned to the lower Ire· que,ncies, regeneration is maintained by advancing the REGENERA· TION knob. R , is a grid.biasing resistAlr. C,andC. areneutralizing capacitors serving W compensate for the interelectrode capacitance of th& d. amplifier tubes. C u, Cu , c.., and c.. are bypass capac-

31 0.., II""" UNIV,~\lTY Of (AllfORNIA

BlONA!. COftP8

itore. r... is a radio-frequency choke coil serving to ple.6nt radio­frequency currents from passing over to the audio-freqtM'Y!)' aide of the circuit.

SO. Circuit elements (fig. 14) . II. Radio control boz BO-t36 or BO fJ35-A.

0.. c..p&c:Itor <:A- lIT- A, .11,.,. e. c..p&c:Itor CA.- lIT- A, ./l,ol. II. IDterrupter BZ-Il E, Ee7 R. Ralttor RS-l\8, ~ ohma S, Swltcb SW-I08

b. Radio receive,. BO-tn7 or BO en-A. Co Ca~cltor CA-I82, 150 ""r. 0. Ca~dtor CA.- I82, 16O.....t. Co Capacitor CA.-t82, lOO.....t. Co CJ,~dtor CA-2:52, f-OO.....t. Co Ca~cilor CA.- 2:I2, f-OO,.,.t. C. CJ,padtor CA.-2M!, 4-OO,.,.t. Co C.pacltor CA-Zlil , S-W ,...t. C. Capadtor CA.-2fil, 3-215.....t. C. CapICitor CA.- 252, 4-OO~~r. c,. Capacitor CA.-ISO, 6-100,.,.t.. c.. CaPfleltor CA.- tIT- A,.!I,.,. e.. C.~cltor CA.-I77- A, .11 ~t.

c,. CaPlieltor CA.- liS2, 100 ,.,.r. c,..CJ,pacitor CA._1711, .002 ~t. Co. CaPllcltor CA.-IT7-A,.ll ,.t. r.. Coli (tim radlo-trequeDc), tranllformer) r.. eon (MlCOtid radlo-trequenc7 traustol"mft) r.. Coli (~teclor tr&Wlformer ) r..eon ~1 p, PlUC PL-81 P. PlUC PL-416 ft, 1leI!1'lor RS-3. 2 m1phmll R, Rh_t.t R 'l-I0t-A, 1 ohm; S, Swltcb SW- IOIl T, Audlo-transl'ormer ~ T. Andl ... transl'ormer C-«I T. Output tr&n.ronm'r Q-82 V, Voltmeter 18-116 J, ,.d, JK-30 C. Lamp LM-3t. 283 1"011a, .'Z1lmpeno Mud. No. 10

c. Rodio tranamitter BO-tf8 or BO-MB-A. C, Cllpadtor CA.- 183, .01,.,. e. CaPlidtor CA.-l~ .01 ,.,. C.Capadtor CA.-21'7, 2llO,.,.t. 0. Oal*1tQr C·..,11f,.002,.t.

,

89 Dn9. II""" UNIV,~\lTY Of (AllfORNIA

•

• • " . . . . "

RADIO 8ET IeR-IOa

CIa Capacltor 0A-11".002 1'1. e. Ca~c1tor CA.-176,.006 1'1. e. C.pacltor CA-263, 200 ""f. C. C.paclIOZ' CA.-1St, 4OO,.,.t. e. c.pu.dtor CA.-2M, 00 py4. e,. c.pacttor CA.-u.6, ro~. c... C.pacitorCA.- I83, 01,.t. e,. Capacitor CA- l83, .01 1'1. c.. Capacitor OA-Iss, .01 Jd. Co. c.po.eitor CA-I83,.01,.t. L, Coli, anlenna <'ODpllnj' 1.0 Coli, JIO"fer ampillier tau: 1.. COU C-92 L.CotI C-8O I..COU 0-103 t. Coli C-I03 1.. Coil, a"leDna 10RdlUl' &. Rea\stor P B-US, ~ooo 0111:9 R. Relmtor P8-9II, 10,000 obm. &. Re8IRIOl' Pl3-OO, 10.000 olmul R. P ..... <rtor P&-2o Im~m R. Resistor PS-1l2o 20 ohm. Ro Rea:I,tor PS-lSS, 3,000 ohn\.l RL Bejar BK-6 J, JlcIt JK-31 (ker) J. Jack JK-82 (micropbone) S. Swltcb SW_IOf T, 'lD.DlIformer 0-107 A "mmeter 18-120, nd\Q.~uency, 1.!hmperetl MA. MllUa.mmeter IS-US. dlrect-curf'eot, 200 mllU..llIpe ....

d. B(XIJBX-JforBX- Jf-&. Co C.pacllor CA.-I77_A,..G /lot.

e. G~ON-J6. Co c.pe.eltor CA.-no. 4,.t. a. p ",llf.or, 23 obms Po ReI1JJtor, 20 obm'

SlCTION IV

TIl 11-239 8O::n

SUPPLEMENTARY DATA AND PARTS LIST

Pa .... napll Qperatlnl' CUrn!ota of Mldio lranlllllilter 8 0-228 or IIO-22S-A ____________ 81 Vol~ and curreota of generator ON-/I.!I ____ _____ __ ____________ ____ S2

OImenlf.ollll and volume ot principal partll. ________ _____________________ S3 Q"lotidea, welgblll, Ind loading of partB on frlme n-l-lS or FM-l8--A..____ 34 Plrl, 1111 ______ __ ___________ _____________ ___ ______ _____________ . ___ 3:!

31. Operating currents of radio transm.1tter B0-228 or BO-228 A The value6 given below are avera~ values and will servlj

88 0.., II""" UNIV,~\lTY Of (AllfORNIA

'l'JI[ 11-S39 ..... SIGNAL CORPS

to indiea.te the approDmate readings that will be obt&ined lVhen the trarunnitter is operating properly. Modulation on tone is 70 percent and on voice is 1)5 percent.

Q.. J.n.e""'114 current-radio I~guency.

cw ... ".· .. , • r..q......,. 'n ~tb:, , ,

c . • . ,- "-2200 ____ ___ __________________________________ _

, .. , " . " 2600 __ •• __ __ • ___ __ ______________ ________ _____ _ , " , " . 08 3000 ____ '. __________________ _____ ___ ___________ , " .08 ...

b. Pl4ttJ~.

C'aomo' til .... )H. ,.. r..q ... ",,~ In kllw:; , .

c, • . ,- .-2200. _______________________________________ __

" .. .. 2600 ____ __________ _________________ ___________

" " " 9000 ________________________________________ __

" " " 32. Voltagn: and CUlT'ents of generator GN--3~.-The follow­

ing values should normally be SI:lCUred at cnwk spoods vllorying from 60 to 70 revolutions per minute. The ripple voltage on the high­voltage side. should not. e.xceed 2 percent..

a. Low-voltage side. 8.00 to 8.25 volta, 2.6 amperes. b. High-voltage side, 825 to 365 volts, 0.1 ampere. c. The nOnlllloi value. is S4(I volts. 33. Dimensions and volume at princlpal parta.-Theee values

ani bued on over-all dimensions. .

DI .... _I .. I_ .-~ ,n ... 1>10 'I\·t.ftb n.l&h, ~ ... -

Radio tranamitter Bc-m or BC-22S-A._ 19. 7~ ,.00 &00 ... Radio recoeiver BC-227 or BC-227- A _____ .. '" .'" &00 ,M Radio OOIltrol box BC-235 or BC-236-A __ HI. Z5 ." ." ," Box BX- 12 or BX-l~A _______________ HI. 25 7. 7~ 7, '" , M Generator GN-35 ______ __________ ______ ." &00 ." , 01 Frame FM- IS Or FM-IS-A ____________ _ 3<00 "'''' ... '" ,., . Bldle_t BCR-203 completely I robled __ 37. 00 >1.00 87, 00 ,.,.

3ft 0.., 1/""" UNIV,~\lTY Of (AllfORNIA

lUDIO SET BCR-203 TM 11-239

" 34. Quantltle •• welght., and loading ot parts on trame

FX-18 " :nt-IS • • Q ..... tI., ~-

, ,.,.",., FM- 18 0, FM- I8-A ___ __ •...•.•••••.•. . •••..• . , Cove' BG-70-A_ ••• _ 0- _ _ _ _ ___ ___ _ •• • __ • ____ •• _ . _ • • __

To,

, Bo. BX-12 or BX- I2-A ..-Ith batter;", ~pa ... t ube., and Iamp ______ ______ ___________ . ________ . _. __ . __ ___ . , Generator

GN-M __ _ . ___ __________________ . _____ . _._ , Co'" CO-203 ___ • ______________ . _________________ ._

• , inlul&tor I~-9I ______ •• _ • •• _ •. • _._._ •. • .•. _ .•. __ •. _

Tot&! 011 top .. _ '. 0- - ••• --- • •• • - •• --- -- _ - .... --I Nm • "" , ..", reeeiver 80.227 ., BC-227- A 'A·lth '0"" .. , Uunp __________ . __ . __ . __ ___ . ___ ._. ___ . __ . . _ . •••. .. , .." , control b .. BC-235 or Bo.235-A ______ 0- _ ___ _ _ _

, , Co'" CO-I99 __ .... _ .. _______________________ . ___ . __ , , enm" ~2_. __ .. _. __ ._ .. ___________ __ __ ___________ , , Go, GY- l L _____ __________ . ___ .• ___ • ______________ _ , , Go, GY-12 ____________________ . ___ ._ • . . _ •. __ . ______ , , Key

J-4~ __ ___________________ _____ • ___ ____ . _____ . __ , , .." RL-28 _______ . ________________________________ +

, • , ... , GP-27 . _ . __ _ ._ .. __ . __ ___ ____________________ __

(') W"" W- IU, IS feet. •• __ • __ . ___________ __________ __ _

T,""' ,. ne&r~de_ ••• ____ __________ ______ ___ __

O§nd.

, Radio transmitter Bo.2ZS or Bo.228-A, tuwln plaee ___

Mwt.eetiono M8-49 to M8-66 and roU BG-Mo. 8G-66-"_ , , Crank ute~ion GG--3 ___________ _____ _____ __ ___ ___ . _

, , He.doet P- 18 _____ .. ________ ____ ____ ____ ____________ , , Tool equipment T~ __ ... _ .. ___ _____ .. ________ ______ , , Microphone T- 17 ___ -+_ 0- . _ .. _ • • _ ... ___ ••• _ . _. _ . _____

To"'l on olhide .............. _ ..... _____ _____ _

T,W "-e1Iht of oet ______ .... __ .. ________ • ____ __

'T_ pono ... _ ID tI,.".., podI • • oltbo_ . • ~ pono ....... 1od ID !.boom podI.' uI .bot ... ",.

On9. II""" UNIV,~\lTY Of (AllfORNIA

""lob' 10 P"OIo<I.

" 00 • ,

'"

,.. " 21. 00

· '" ,. " 47. 35

.. . .. • '" '00

• 88 • " · " ' . 00 ... , ... '" -.. " """ ... , .. '00 , . .. ,. '"

37.n

. 162. 00

TIt 11-239 .. SlGNAL CORPS

35. Pam It-t.- For complete information r;ee Signal Corps General Cat&log.

, • , ,

BaUerie!! flA-2. nO "pMIlII ___ __ _______ ___ __________ _

Br.tterle.. BA- 23. nO spr.""' ____________________ _____ _ Battery 5A-27. no .pareII __ _______ __ __________ __ ____ _

BoI BX-12 or BX-I2-A for br.tterlee and spare tUbee __

1 Radio Cootrol Bo~ BC-235 o. BC-23a-A ____ __ ___ ___ _

1 Radio Reeeive. BC-227 or BC-227-A ___________ ____ _

1 Radio Transmitter BC-228 or BC-228-A ____________ _

I Reel RL-28 ___ __ ____ . _____ _______ ____ ______ ____ __ _

1 Roll BG-M Or BG-M--A (tor maet IleCtioIl$) _ ___ _____ _

3.0 3A23 SA"

2Z1112

" 2Z1112A

2Z3370

" 2Z3370A 3Hlf02 2"... 2~18

" 2U618A

,a".. 2A1311 2AI812

2B918 8A3«1I

""'"" 2A2349 2.0"" 2A2351 2A23S2 2A= 2A23M 2-"'" 2.",. 2BI617

""2M o.

W32MA ",.,,, " 2C<mA

2C0228

" 206228,\ 2A3128

""'" 'WbOD <'",,'0 or b • • doo, P-18 .re nb .... ted. bead .. , HII-:lS ."" ""rd CD-307_J., 84 iD .... 1001. mOT be U bollnte<l.

3_6 0.., II""" UNIV,~\lTY Of (,I.lIfOll~JA

.. . . .. . MDIO BCT BCR-20a

• Stake.OP-27, 31n U"",. I .~- _______ _ • _____ __ ____ _ I Tool equipmen\ TE-h __ ___ ____ __ __________ __ ___ ___ _ 8 Tubeo!l VT-U,lIln \Lee, 3op.ate ____________________ _ _ 3 Tube!! VT- 215, 2ln uoe, 1 ,pare __ _________ __________ _

2 TllbM VT-liO,llnuoe, 1 a~-- -- :-- - -- - - -- - - ----- -I Voltammet.er 1-60 ____ _______ ______ ______ ____ _____ _ 18 r""t Wire W- 12. ___ . __ ___ ____ ____ _______ ________ _____ _

[A.. G. 082.11 (4-1$-41) .)

By ORnER OT THJ: SlCllP:T,UIT or W AA:

TlI[ 11-839 .. 2A8327

",""" "'" ".,. >TOO

" .... IBIU

G. C. MARSHATJ., .OhUj of Staff. . .

Onrow., E. S. ADAMS,

Major Gemral, T~ Adjutant GeMJml..

IhImlIBUTION :

ICandH2,8,1l {til. (For upla.nation of symbols see FM 21-4)

. , ,

,

, " . . . . . . ..... 11 •• " ..... " "'" ".,

0.., Ilmm UNIV,~\lTY Of (AllfORNIA