Receiver Audio Amplifier Module A25

is also applied to tone squelch module A24

tively. Resistors R17 and R21 are

collector load resistors for Q4 and

(para 11). The collector signal of amplifier

Q1 is fed back through coupling capacitor

Q5, respectively.

C3 and voltage dropping resistor R1 to the

c. Receiver Discriminator Driver Q6.

The receiver discriminator driver ampli-

base of Q1 to supply a small amount of de-

fies and limits the 11.5-mc if. signal output

generative feedback to minimize audio dis-

from Q5 and applies a strong signal of con-

tortion, and to prevent discriminator load-

ing by presenting a relatively high input

stant amplitude to discriminator Z1 (fig.

impedance to Z1.

88).

(1) The 11.5-mc signal from Q5 is

b. The audio signal at the moving contact

of the VOLUME control is applied through

coupled through capacitor C15 to

coupling capacitor C5 and isolation resis -

the base of Q6. The output of the

driver is developed across a tuned

tor R5 to the base of receiver audio output

amplifier Q2. The output signal at the col-

circuit consisting of capacitor C18

lector of amplifier Q2 is applied to the

and the primary of coupling trans -

former T2. The secondary of trans-

primary of audio transformer T1. The au-

former T2 and the tuned circuit

dio signal is applied from the secondary

of T1 to the handset through the contacts

consisting of capacitor C21 and

variable inductor L4 match the out-

of squelch relay K3 (fig. 88).

put impedance of driver Q6 to the

c. Capacitor C2 is an rf bypass in the

input impedance of discriminator

input circuit. The combination of resistors

Z1. Resistor R25 and capacitor C19

R2 and R3 provides fixed base-to-emitter

form a compensating network which

bias for Q1. The combination of resistors

improves the response and linear-

R7 and R8 provides fixed base-to-emitter

ity of the input signal to Z1.

bias for Q2. Resistor R10 is the collector

voltage dropping resistor. Capacitor C7 is

(2) Resistors R22 and R23 develop the

a bypass capacitor for noise. Resistor R9

base-to-emitter bias for driver

is the emitter swamping resistor; capac-

Q6. Resistor R24 is the emitter

itor C6 is the emitter bypass capacitor.

swamping resistor and capacitor

Resistor R11 presents a constant output

C16 is the emitter bypass. Resis-

impedance to Q2 when function switch S1

tor R26 is a filter resistor in the

(fig. 88) is in the SQUELCH position and

+10-volt supply line. The combina-

there is no incoming signal. The input sig-

tion of capacitors C17, C13, and

nal to module A25 can be measured at test

inductor L3 prevent rf leakage into

jack J3. Resistor R12 isolates the input

the supply. The output is coupled

circuit of transistor Q1 from external

through capacitor C20 to Z1. The

loads introduced at test jack J3. The output

output from T2 can be measured

signal from module A25 can be measured

at test point J4.

at test jack J4.

d. During transmission, the sidetone au-

10. Receiver Audio Amplifier Module A25

dio from module A22 is coupled through

(fig. 4)

capacitor C8 to the input circuit of Q1.

e. Capacitor C11 (in the mainframe (fig.

Receiver audio amplifier module A25

88)) is an rf bypass capacitor on the +10-

amplifies the audio output from the 11.5-

volt regulated input to module A25.

mc discriminator, Z1, and applies it to the

handset.

a. The audio output from Z1 is coupled

11. Tone Squelch Module A24

through coupling capacitor Cl to the base

(fig. 5)

of receiver first audio amplifier Q1. The

a. When the function switch on the front

output signal from Q1 is developed across

panel is at SQUELCH, +10 volts dc is ap-

collector load resistor R4 and is coupled

through capacitor C4 to VOLUME control

plied to the tone squelch module. Squelch

input amplifier Q1 and squelch emitter fol-

R1 on the front panel (fig. 88). This signal