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Page Title: Receiver Audio Amplifier Module A25
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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.
(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
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
a. The audio output from Z1 is coupled
11. Tone Squelch Module A24
through coupling capacitor Cl to the base
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

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