RADIO SET AN/ARC-131 INTERUNIT CIRCUIT DETAILS-continued

TM 11-5820-670-30

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

In T/R mode, primary + 27.5 vdc power is applied from pins C, D, and E of control unit connector

J9101 to contacts 1,2,3, and 5 of S9105D front. Primary power is connected through the switch to

contacts 9, 10, 11, and 12 to pins F, e, and f of control unit connector J9101. Primary power is then

coupled through the aircraft wiring, to receiver-transmitter connector P9801, where it is connected

through pins 18, 34, and 36 to pins 1, 2, and 9 of connector P9501.

Primary power is applied through fuses F9502 and F9501 to the regulator circuits which provide

+24 vdc necessary to operate the radio set. Power is also applied through reverse-voltage protection

diode CR9504 to all receiver-transmitter relays for relay operate power.

In T/R mode, transmit audio signals originate at the microphone and are coupled through the aircraft

interphone set and interconnecting cabling to pin y of control unit connector J9101. The audio is then

coupled through S9105C rear from contact 11 to contact 10 and out of the control unit through pin X.

The audio common is connected through the control unit from pin kk to S9105C rear contact 5, from

contact 5 to contact 4, and then out pin d of the control unit connector.

Transmit audio (high) is coupled from pin X of the control unit connector to pin 6 of receiver-

transmitter connector P9601. The audio common is coupled from pin d of the control unit connector to

pin 5 of receiver-transmitter connector P9601. The audio signal at pins 6 (high) and 5 (low) is

coupled into the amplifier modulator through relay K9606 contacts 2 and 4 and P8701 pins 7 (high)

and 11 (low) to the audio mixer. The amplifier-modulator modulates the carrier with the audio signal

for transmission.

Received audio is coupled from the audio output transformer in the audio frequency amplifier, through

pins 2 (high) and 8 (low) of P5501, to pins 13 (high) and 14 (low) of receiver-transmitter unit con-

nector J9601. The received audio (high) is then coupled to control unit connector J9101 pin JJ while

the received audio (low) is coupled into the control unit through J9101 pin B.

Received audio (high) is connected through S9505C front from contact 1 to contact 2 then through

VOL control R9103. The signal is coupled from the wiper arm of R9103 to pin N of control unit con-

nector J9101. The received audio (low) is coupled through S9105C front from contact 7 to contact 8

and then to the audio common line at pin KK of control unit connector J9101. The received audio (high

and low) is then coupled through the aircraft interphone set to the headset.

In T/R mode, the receiver-transmitter is in receive condition, except when the transmit button is

pressed. When the transmit button is pressed, a ground is supplied through the aircraft interphone set

to pin g of control unit connector J9101. The ground is then connected through S9105A front from

contact 3 to contact 2. From contact 2, the ground is connected to pin v of control unit connector

J9101 and then to pin 41 of receiver-transmitter connector P9601. From pin 41, the ground is applied

to the coil of relay K9602 causing it to energize. Relay K9602, in turn, activates the transmit mode

relays in the receiver-transmitter.

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