c. Power Supply. The chart below lists the circuits energized when TEL-RAD-RAD/SPKR switch S202 is in
the position indicated.
Audio amplifiers Q201 and Q202.
Audio driver Q203.
Power amplifier Q206.
d. Sidetone. During telephone communication or transmission of voice signals through the radio set, a
sidetone signal developed in the H-138/U microphone is applied to the H-138/U earpiece.
(1) TEL position. Voice signals developed in the H-138/U microphone are applied through audio line
transformer T201, switch S202, to the H-138/U earpiece.
(2) RAD or RAD/SPKR position. Voice signals developed in the H-138/U microphone are applied through
audio line transformer T201, switch S202, filter FL201, VOLUME control R208, audio driver Q203, audio
transformer T202, relay K201 (deenergized), and switch S202, to the H-138/U earpiece.
1-1 3. Stage Analysis of Remote Control Unit C-2328(*)/GRA-39 (figures FO-1 through FO-4)
The following discussion applies to all models of Control, Radio Set C-2328(*)/GRA-39,
except where noted.
Refer to schematic diagrams FO-1, FO-2, FO-3 and FO-4 for minor differences between
The setting of the TEL-RAD-RAD/SPKR switch determines the distribution of battery
voltage to the stages in a. through e. below. This action is described in paragraph 1-14.
a. Preamplifier (Q201 and Q202). Audio amplifiers Q201 and Q202 amplify the low level audio signals,
developed in the handset microphone, by approximately 57 decibels (dB).
(1) Audio amplifier Q201. When the handset push-to-talk switch is pressed, audio signals developed by the
handset microphone are applied to pin D of J201 and pin A of P201. The audio signals at pin A of J204 are
coupled by capacitor C201 to the base of Q201. The amplifier audio output of Q201 is coupled by capacitor C204
to the base of audio amplifier Q202. Resistors R201 and R205 forma voltage divider to establish the
base-to-emitter forward bias. Battery voltage is applied to Q201 through emitter swamping resistor R202
bypassed by capacitor C202. Resistor R206 is the collector load resistor. Capacitor C203 shapes the high
frequency output response of Q201.