AUDIO CIRCUITS

TM 11-5820-670-30

1-60. RADIO SET AN/ARC-131 INTERUNIT CIRCUIT DETAILS. (CONT)

AUDIO CIRCUITS

See FO-15 while reading this section.

Audio signals from the microphone are coupled through the interphone amplifier to pins y (high) and

kk (low) of control unit connector J9101. The 110 ohm and 43 ohm resistors form an impedance

The audio signal is then coupled through mode control switch S9105. The audio high line is coupled

through contacts 10 and 11 of S9105C rear and the audio common is coupled through contacts 4 and 5

of S9105C rear. The transmit audio signal is then coupled out of the control unit through pins x (high)

and d (low) and through the aircraft electrical harness to the receiver-transmitter.

The signal is coupled into the receiver-transmitter electrical connector P9601 at pins 6 (high) and 5

(low). The signal is then coupled through contacts 2 and 4 of dummy relay K9606 to pins 7 (high) and

11 (low) of connector J8701 on the amplifier modulator assembly. From pins 7 and 11 of J8701, the

signal is coupled to the audio mixer.

Received audio is coupled from the output of the receiver-audio amplifier, in the audiofrequency am-

plifier, through pins 2 (high) and 8 (low) of J5501 and P5501 to the receiver-transmitter electrical

connector. The signal is coupled through pins 14 (low) and 13 (high) of P9601 to the aircraft elec-

trical harness, which couples the signal to pins B (low) and JJ (high) of control unit electrical

connector K9101. From pins B and JJ, the signal is coupled through contacts 1 and 2 (high) and 7

and 8 (low) of mode control S9105C front.

Received audio (low) is coupled direct from contact 8 of S9105C front to pin KK of control unit electri-

cal connector J9101. Received audio (high) is coupled to pin N of J9101 through VOL control R9103.

Resistor R9104 prevents the audio level from going to zero when VOL control is adjusted maximum

counterclockwise. From pins KK and N of the control unit electrical connector, the received audio sig-

nal is amplified by the interphone set and then coupled to the operator's headset.

MODE CONTROL CIRCUITS

Radio Set AN/ARC-131 has three modes of operation, transmit/receive (T/R), retransmission

(RETRAN), and homing (HOME). Mode control switch S9105 on the control unit selects the operating

mode. The mode control switch also has an OFF position which removes primary power from the

receiver-transmitter.

See FO-16 while reading the text in this section.

Transmit-Receive Mode (T/R)

When mode control switch S9105 is set to T/R, the radio set operates as a two-way fm receiver-

transmitter. The radio set is placed in transmit condition by pressing the transmit button and returns to

receive condition when the transmit button is released.

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