Auxiliary Audio

C2, TM 11-6625-564-45

of transistor Q1. The output of Q1 is devel-

may be injected to the modulator and audio

module in the receiver-transmitter in this

oped across collector load resistor R8 and cou-

manner.

pled through capacitor C6 to the base of tran-

sistor Q2. The signal is then consecutively

amplified by and coupled to succeeding tran-

1-28. Auxiliary Audio

sistor stages Q3 and Q4 and finally to out-

(fig. 4-10)

put transformer T2.

a. The +27.5 volts dc supplied to audio am-

The auxiliary (aux) audio signal produced

plifier 3A1 is applied to the collectors of tran-

in the receiver-transmitter is applied through

sistors Q1, Q2, Q3, and Q4 through voltage-

pin L of connector J2 to a simulated adf load

regulating circuit resistor R6 and Zener diode

consisting of capacitor C3, resistors R4 and

CR1 and voltage-dividing network R2, R3,

R5, and diodes CR2 and CR3. AUX AUDIO

R4, and R5. Capacitors C2 through C5 are

jacks J10 and J11 (J11 is ground) serve as test

decoupling capacitors used with resistors R2

points to check aux audio voltage across the

through R5 to keep the audio stages from in-

load.

teracting with each other. Capacitors C6, C7,

C8 are coupling and dc blocking capacitors.

1-29. SENSITIVITY Control and Squelch

Resistors R8, R10, and R12 are collector load

Disable

resistors.

(fig. 4-11)

b. Resistors R7 and R14, R9 and R15, R11

and R17, and R13 and R18 are voltage dividers

SENSITIVITY potentiometer R4 is con-

to provide base emitter forward bias for tran-

nected to the sensitivity control in the receiver-

sistors Q1, Q2, Q3, and Q4, respectively. Re-

transmitter through pins B of plug P1 and

sistors, R20, R22, R23, and R25 and capacitor

connector J6 and pin Z of connector J6. The

Cl2 form an automatic volume control (avc)

sensitivity of the receiver-transmitter can be

network for the emitters of transistors Q1

varied by rotating SENSITIVITY potentiome-

and Q3. When the ac signal output increases

ter R4. When SENSITIVITY potentiometer

at the output of Q4, the net forward bias of

R4 is rotated to its extreme clockwise posi-

Q1 and Q3 is reduced, thereby automatically

tion, SQ. DIS switch S5 is closed and applies

decreasing the gain. Capacitor C9 suppresses

a ground to squelch relay K1 in the receiver-

noise that may be present at the base of Q4.

transmitter through pins H of plug P1 and

Resistors R21, R16, R24, and R19 are emitter-

connector J6 and pin a of connector J2. This

swamping resistors, used to temperature stabi-

disables the squelch action of the receiver-

lize the emitter current. Capacitors C13, C10,

transmitter.

C14, and C11 are for the purpose of bypassing

the signal around the emitter-swamping

1-30. Frequency Selection Action

resistors.

(fig. 4-11)

c. Output transformer T2 applies the audio

The control head portion of the test unit

signal, to MIC SELECT switch S2. When this

switch is set to HDSET, the audio signal from

contains three FREQ SELECT switches: S1,

S2, and S3. These switches perform identically

audio amplifier module 1A3 is connected by

MIC SELECT switch S2 to the modulator

as their counterparts in the radio set control.

and audio module A4 in the receiver-trans-

The switches apply a ground potential to the

mitter through pins E and V of connector

relays of the mechanical tuner in the receiver-

transmitter through pins K, W, V, U, Z, X,

J2. When MIC SELECT switch S2 is in the

DUM MIC position, the audio amplifier mod-

M, a, d, T, c, b, g, f, j, Y, h and s of plug,

ule is disconnected from, and DUM MIC

P1 and connector J6, and pins X, P, V, U,

jacks J16 and 517 are connected to, pins E and

T, c, b, L, M, K, N, J, Y, F, Z, H, a, and

S of connector J1. F R E Q S E L E C T s w i t c h S 1

V on connector J2. An external audio signal,

changes the receiver-transmitter frequency in

such as that produced in an audio oscillator,