Racal 121B, 121A Service manual

Nc2t.

Eeer

lf

3eg

INDEPTNDENT

TYPE

Op.letiDg

Tachlical
RACAI,

ELECTRONICS

'Wcatern

B!acloell,

ADAPTOR

RA. IZ IA/B

aad

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llaldbookr

Road,

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Englard.

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Racal

Copyright

Prtntcd iD

Eaglaad.

GOncenn

all

usens

of

electnical equipment

fnom

different

a

point

of

vtew

a

read

caref

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... it

incase

of Electric Shock

FI G.1

FIG.4

.:

SEND

1.

sWfCH oFF. n

PROTECT
ing motcriol ond
the condu ctor.

DON'T
BARE HANDS
conductor, bul DON'T

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sidc.orms bcnt ond

to

kacp

(6)

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hond

(c)

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thcn omit thc
thc movcmcnt

HAYE

SOMEONE

ELSE

FOR DOCTOR

YOURSELF

TOUCH THE

poticnt

mouth ond

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your

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honds on his shotrld.r bldd€9

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bockwords

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down

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of thc

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(s.c

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KEEP PATI€NT

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FOR TI|OEE tlJ}|O

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SUFtiC:i:i.,

EVERY REASONAALE PR€CAUTION

IN DESIGN

ED

fhe Power

WHEN MA

TO SAFEGUARO OPERATING PERSONNEL.

BEFORE SE RV!CING €QUIPMEN

GREAf

K ING INTERNAL ADJUSTMENTS-EIC.I

LIVE

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IIi3ANGER HUMAN LIFE.

BE

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HAS B€EN OBSERV-

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OFF

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TWITCII OFF

PLAY SAFE

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proceed

with

IIANDBOOK CI{ANGE INFORMATION

At ILACAL,
with the latest electroDic developlllents by adding
circiiit
rneDt3.

requirernents,

'change

your
on tollowiug

and component

SometimeB,

! imme diately into

handbook lnay contaiD new change

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we

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urrable to

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NOIES

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$_A-8 TF_R_ _ 3_

BRIEF

Int!oduction

1.
in
ation of the adapto!, Chapte!
be !ead.

Mixe!

Z. AtL input eignal

Iato! i6-variable ove!
provides all acculate control of
the ca!lie!

and to avoid
position

FiLt€!s and

Thi6

figure l, the-basic theo.y

rnixed with the output

6ection brielly

and O6ci11ato!

and unwanted sideband

pitch

switch

Ca!!ie!

distoltion.

alte!s the frequency by

TECHNIC

desclibes,

of 6pelation. Fo!

5

100

at

tZ kc/s and is fitted

Rejection Bri.dqe.

kc/s,

ot a Etable

A

at_

(Detailed

fed

tuning; essential to take fuU

rejection chalacte!istics o{.the

further control in the folrn of

P=E=s=c=E !E 3.r 9y=

with

Cilcuit

via

118

t 3

aid of the block diaglam

the

a fully detailed expla!-

Descliption)

preset potetrtiomete!, ie

a

kc/s oecillator. This
with a slow rnotiod dlive

kc/s.

shouLd

o6cil-

which

advantage of

unit,

a three

l8

3. The rnixer output centred
(18

kc/s r 6 kc/s)
and an amplifier stage to both upper
filters plovide a high deglee oJ rejection to
wanted

Ploduct Detector5

4-

including an audio frequency cornponent. Unwanted
ale subEequently
resultant output therefo!e

sideband.

Each
signal

Eideband

at l8

and

kc/s,

removed

band-pasE filte!, car!ie!

Calrier

til.ter output is mixed

frorn a fixed frequency

by means of a further

consists only ol the

on

!e-i.nsertion Oscillato!

kc/s,

and 1ow€r ridebaDd filte!6. The

is fed via a lZ to

lejection blidge

aLl signals othe! than

ploduct

in a

oscillato!,

fllter net$/oik. The

audio frequencies.

Asg&-EEcer-

5,

plovided

The
a

audio Jlequency on each channel

gain

control and having three

\rith a

6witch for

sideband selection.

independent outputs, one

is fed to an

detector,

signal

a.

f.

24

kcls

stage

the

\vith
giving
ftequencies

outPut stage

oI

a

Ploducts

which

with

is

RA.

121

Section,

1.

Indicalor( c.

c,

t.

)

6.

Ac.r,t.

tu.actions

le-insertion
carlie! signal,
thlough.a

ghowirg

fi!6t'mixe!,
oscillato!,

two-stage

a stationaly

1s thc

(18

kc/i)

Audio F!equencv

?. A sirnple

correct
o! the intehal

tuning

6rciltators.

osqillato!

taken

6ame

cont!o1

folln

aa a tlrnlng

outPut

florn

tuned

the band-Pass

amplifie!. This

ellipss'when

as the

when turing o{ the

i. e.

a. f,

of

over

c.

a small range

indicato!. The

aPPlied to the

is

filtel

i5

gives a

the inPut carrier

fleduency of

the calriei re-inBeltion

iaput Eignal

provided fo! oPtional

ie

of dlift

18kc/scalrie!

X-Plates

aPPlied to the

Lissajous

frequency'

is co!!ect.

use to

of eithe! the

and t}te iaPut

Y-Plates

Presentation

afte! the

rdaintain

input 6ignal

RA. l2 L

Section

'i.F-:....-

l,

Chapter

l.-,,- :'

-.-"..,-.-

=cJ=4gJ=E=E=s.

=D*E +i !=E+

Mixe!

118

Baad-Pass

Ca!!ie!

Sideband amplifie!

Sideband lilters

Switching to

of

P!oduct

Stage

kc/6 Oscillato!

Filte!

Rejcction Bridge

provide

L t?

RA.

detectors

=c=Lqg

C ONTENTS

for

Sideband

gI

I=

Invel8lon

p=E=si=E

!E T=r

g\

L

4-6

l0 - rl

Audio outp\rts

Ca!rie! !e-inse!tion

Cathode-follower

AmnliaiA- 26A . f

c. !.

t.

Indicato!

Powe! supply

O6cillato! and

-

't)

14

|.,

-

t5

RA. lZ 1

Section I

CHAPTER 5

Mixer Stage

l. A 75fl

socket

plovides

Rl

is applied

V2
centled

ll8

kcls

Z.

whilsi a
+2

VZ i8 a catlode eoupled
of ll8

kc/s.

(unbalanced)

PLlz-and aa

a

Fuitable impedaoce rnatch,

via Cll

on 18

fine turri.ng control

kc/9

OsciUator

kc/s. Switched capacitors vary this

Bani-Pass ritter

3.

couples thc l8

the c. !. t,

rejection

This filte! iB a 6ing1e sebtion
ltarn

lZ - 24kcls.

kc/e carrier to

The carrie!

blidge stage.

g3J=L+P

PE

to the suppreEsor grid

is taken flom

= S=I=+q

source of signal at

input

plue

potentiornete!

the anode,

Colpitt6 cilcuit opelating at a

C3 coupled to a slow inotion

L tuned !.J.

alt

arnplifie!

sidebandc

g=IT

constant K have a

ttanEfolmer i1:. selies with

is appli.ed

DESCRIPTION

100 kc/s is

RVt to the signal grid

The output oI a Il8

of

Vl. The resultant

V3 aild thence the

Il-lg:--ll

coErected via

kc/6 oscillator

norni.nal frequency

fiequency by * 3

dli.ve

senEibly flat response

via

C20

varieg

plate3

Y

to the calrie!

-

of Vl.

output

kc/5

it by

the tilto!

of

Ca!!ie!

4.

the bridge
loDger

available.

5.

6.

could ocLur if the

Reiection

V4 togethe! with
ci.rcui.t

!e6onant, its i impedance

RV3

The
beat

L9, C4Z

so the!e is no output.

ple6et

is a

308

lejection

note

with

B ridge.

R22, L9,

is resonant

control

plovided

the ca!!ie! re-insertion

carrier

level

C4Z, R2I

at l8

At the sideband frequencies

unbalances the bridge and an.output

which

ensules alt accurate

plevents

was

at

and

RV3

kc/s

or near the

and

it6 dynarnic impedance balances

the

caft'ier ftorn ploducing an audio-

oscillato! at

foln a b!idge.'

L9,

balance at 18

a later stage.

eideband leve1.

Thc

C42

is

tuned

is no

kc/s.

This

RA.

lZl

Section

l.

PiIoL car!i er systerns.

lZ.

This

where

heading

the ca!!ie!

cove!s

is ttansIni.tted 0

single

of theae signals is accomplished
carlie!

13.

.

wheD

14- With

(Pa;as.

Tlre Y GAIN contlol olt the
and

the receivet gain

pilot

the

indbpendeat

the calrier

however., an

recelve! Bo
the sideband fa11s
not

essential, but

L?

RL

to be

rnodiJic-ation

15.

For

lccelving lowe! sidebands,

highet

the

of
bandvddth,
receiver

signal to

the adapto!

is

set to the !equired bandwidth (3
catrle! is apploximatcly
in the
tuning

tuning indicato!,

contlol, but

?

to I l).

set to give a full

cart.ie! is tuned to give an

sideband emission,

lies Dear the

implovernent rnay

that the

carrier

lies

symmetricaUy

may help irl the caseg

6et to a nalrowe! bandwidth,

to

the tunirtg

plocedule

flequency, .b). an amount

be received.

main tuning

on tune, as indi.cated

FinaL

only a 3mall amount

sideband and

to

in a similar

l2lA/B

RA.

independent sideband

-Z6dB

below nolrnal

rnanner to those witll

should be set

screen display

ellipse,

the receiver

centre of its

golrretimes

to one side

within

pass-ba;d.

be obtained by tuning the

ofitg

pa66-band,

the available band width.

of intetfelence since it allows

and in o!de!

iE

neceBsa!y.

the adaptor tunilrg

corre6ponding to hau the band*'idth

For exanple, w.ith an

contlo! id set to +1.5

kc/s)

and

by the rise in amplitude

preci6e

tuning is

carried out on the adapto!

of adju8tlltent should be neces€a!y.

.sigDals

1evdt.

a fult

Dea! rnaxilnu-ltr,

on the c. !.t.

witl

be iuned so

Fo!

s,

a. b.

signals,

i.e. so that

ThiE

the

achieve

to

it a slight

isAiatiaet to a

l. E. b. Bignal of akc/s

kc/s, The

tuned until the

pilot

I'unUg

that

is

16.

-

capacito!
a

l?.

To take signals with
flortt zelo.

covers only tZ

switch

plovided

is

Fo! uppe!
detuned

16.

The use of thi6

po65i.b1e

Svstems with

19.

No sln-rple ri:ell:od

is avai.lable

be

tuned by

ear.

6kc/s sidebandB

pleselve

To

kc/s.

which gives

a

slow tuning
Ilr order to
a

furthe! t3

sidebands the above procedu!e

to the l.

side

f.

detuning

of zelo.

procedure

intelmodulation products

completely

{or the tuning

supp:essed

ci runing

these signals i.s i{:lown,

indicator to wo!k

carrier.

the adaptor is detuned 3

late howeve!, thc main tuning

cove!

a g!eate!

kc/6,

is adopted with t}Ie adapto!

helps

from adjacent

with

the ieduction of any

Etlong signals.

No

on, so these signals must

kc/E

range tban thiE,

piloi

carrier

RA.

I2I

Sectlon

r,

LhaPlel

J.

20.

Listening

centred on the

be

the RA,

to

pass-band,
then adjusted slowly until
whethe!

listen

to each

recognize

pleBdttt

not

the signal

the

too

is of

output chadtel
chalactelistic

rnuch difficulty.

17

outPut,

signal becoaes itrtelligible.-

the

the 1. s.

in turn. With a little
sound

the signal is fitst

judged

by loudness.

b. or u. s. b. variety

Practice

of this tyPe of ernission,

tuned until it

adaptor tuning is

The

If_it

will

it

be
if

is

and tunilg

aPPeals

i5 nof

kno"rr

necessary to

possible

to

wiU

to

21.

ouq)ut

22.

\{he!e the

as above,

channels.

For

the

signal is of the

except

leccptidn

both carlying

6. s. b.

not

6ignale. Sirrce

rleceEsaly to re-inse!t
approximately 50
result.

supPre s

Tuning

sed. car!ie!

ie

that

of double

the same

the

of the collect

c/s

carlied

syatelns.

i. e.b. type,

intelligeace

u'il1

the turliDg

be

eideband suPP!essed

inteltigence) the signals

two. sidebands

the catlier

ate

phase.

in

sePalated

frequency an

out ill exactly

the eame

obtained

ale tleated

Providing
intelligible

way as

i3

carlied

out

PleciEely

florn both sidebaDd

calrie!

signals

as nolmal

in the

adaPto!; it i5

it is

withilt

signa).

with

othe!

will

fu]Iy

(i.

e.

..:-.

Section

I,

Chapter

3.

A Bhli {i a- r''l: a

^

14.

The

18

two stage
RVZ is included.
indicato! ald
of the

to

'such

15.

calrie!

the carlie!

locking

Whea

the a.

oEcillato!

by

the arnplifier

c. r. t,

15.

Iidicator

The

c, !. t, op€lates

plesentatiott.
potential
platee
giving

of

the accelelating

can

be adju6ted

X and

Y
V6 iE applied
plate6,

kc/s

calrie! ouq)ut

tuned amplilier

The output

also

via

C30

!ei!6e!tioD

flequency

to

b€ callied

t.

c. is switched

tuned

circuit

output

One X and

by

shift

to the

contlol.

X-ptate.

and

oscillato!

when

out

cilcuit

as

anode

RV3 alrd

frorn

using

is

couPled

tf,le a.

{, c.
V6.

the

carlier

without

off

to

codlpensate

in the

a

tuning

one y plate

whilst

RVS to

The

output

and

thc

arnpUfied

the band-pass

a

triode pentode

.\|ia

CZ9

ON/OFF switch

This locks the

fleque[cy

affecting

and

C3g

t}re inteuigibility

C39

fo!

a.

f. c.

iDdicato!

ON conditi;n.

by

are

strapped

potentlals

the

above
of thc

carrier ie applied

to

the

is

ale

the

capacitance

tneans

and

below

carrier

fi.lter is

V3.

y_plates

to

coupled

gain

A

of

the tuned

oscillato!

trea! enough

of

s\'itchadraclo!!

i.ntlod.uced

of a

Lissajou6

togethe!

on ihc

at

other

the anode potential

!e-inEeltlon

to the

to

a

contlol

the

cr!.

circuit

flequency

to

enable

the signal.

tho

ttre
two

osci,Irato!

y_

t.

Powe!

17.
.:

c, r. t.

Supplv

powe!

The
line

is supplied,

ci!cuits.

supply

is

convendolal,

so that

a

total.

of

except

ueally

that an additioaa].

600 volts is

available

negative

fo!

the

RA. l2l

Section l,

Chapte! 5.

!FS=T

r=9I=

3

l!4r!3F-[4y9=+

CONTENTS

CI{APTER

C!{APT
CI{APTER
CI{APTER

CI'APTER

ER 2

I

3
4
5

TEST

MAIN"ENANCE
VALVE

TEST
ALIGNMENT
COI{PONENTS

EOUIPMENT

DATA

SPECIFICATION

REOUIRED

PROCEDURE

LIST

FOR

RA. l2l.

CHAPTER

1

3=E=s+

+qgJEAAEryS=

=R€g

gI5=Ep=

+9 S=

y4r=l.LT

I

RA.

l2 r

Section

2

CHAPTER

I

1..

Ies=E

The following
enance desc:ibed

(")

(b)

(")

(d)

(e)

(0

Multi-tange
a.

Signal
provide

Valve
D,igitaI.F!cquency

125

Output powet

lOKg,

gyJ=Plg

=E

jterns

c. and

kc / a).

d. c.

cenorator (l0O

?5

Voltincte! (50

watt

+

gI=:a

of

ia thie part

meter (20,

up to

ohrns

rhcte!.

!eslsto!.

*E

test gea.

500

soulce

mV

Mcter (max.

gJJIpp

are

requlred

of

the

bandbookt_

0000/vo1t)

volt8.

kc/s)

etth

lmpcdd,ncer.

to l00V

=E

9&

to

meaauring

a rnatching

r. rn.

f !equcncy

e.

)

Jt+Iry

car!y

devlc6

T=E=\+

out

NCE

t}Ie rnairt_

to

RA. l2l

Section

2.

Int!oductign

S=E+=P+E+.=2=

Y+=LJE=P+J+.

qONTENTS

Pa!a

Ba6c

Valvc

CoDnectlong

complemcnt

aDd

typical

voltagcs

RA. 12l

Section

Z