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Page Title: Speech Amplifier Limiter Module A22
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frame) (fig. 88) at SQUELCH, sidetone au-
cycles of the 150-cps signal will cause
dio is applied to the squelch circuit input,
the amplifier-detector to conduct. The out-
while the 150-cps tone is coupled across
put developed across collector load resis-
isolation resistor R1 and superimposed
tor R18 is a negative-going half-wave
on the sidetone audio signal. This condition
rectified s i g n a 1. The output signal is
permits the operator to hear the sidetone
filtered by capacitor C9 and is directly
in his handset.
coupled to the base of relay driver Q5. The
negative dc signal causes transistor Q5 to
conduct, which causes current to flow
12. Speech Amplifier Limiter Module A22
through the squelch relay winding. When
relay K3 energizes, the receiver circuits
will operate.
The speech amplifier limiter amplifies
the audiofrequency signals from the mi-
c. Capacitor Cl is a bypass for the
crophone section of the handset. This mod-
higher audiofrequencies. The combination
of resistor R14 and capacitor C6 decouples
ule consists of two speech amplifiers and
the emitter circuit of transistor Q3 from
an output limiter stage. The audio output
is applied to sidestep oscillator module
the +10-volt supply. Potentiometer R15,
which is the emitter swamping resistor
A20 (para 14) and sidetone output is sup-
for transistor Q3, is used to adjust the
plied to receiver audio amplifier module
negative feedback to the base of transistor
A25 (para 10).
Q1 through dropping resistor R5 to thereby
a. Audio signals are coupled through an
control amplifier gain. Potentiometer R15
input matching pad consisting of resistor
is normally adjusted so that an audio in-
Rl, inductor L1, and capacitor Cl through
put signal of 35 millivolts minimum causes
coupling capacitor C2 to the base of first
squelch relay K3 to become energized. The
speech amplifier Q1. The amplified audio
combination of the squelch relay coil and
output from the collector of Q1 is applied
resistor R19 provides emitter operating
through coupling capacitor C5 to the base
voltage for relay driver Q5. During trans-
of second speech amplifier Q2. The audio
mission, with function switch S1 (main-
signal output from Q2 is applied through
Figure 5. Tone squelch module A 2 4 , s c h e m a t i c d i a g r a m .

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