Retransmit Mode (RETRAN)

TM 11-5820-670-30

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

In RETRAN mode, + 27.5 vdc primary power is applied through S9105D front to the receiver-

transmitter as indicated in the T/R position except that contact 3 is used instead of contact 5.

Received audio signals are coupled from the receiver-transmitter into control unit connector J9101 at

pins JJ (high) and B (low). The received audio (high) is connected from pin JJ through S9105C front

from contact 1 to contact 3. From contact 3, the received audio (high) is connected to pin A of control

unit connector J9101 then through the interconnecting cabling to radio set no. 2 for retransmission.

Received audio (low) is connected from pin B through S9105C front from contact 7 to contact 9. From

contact 9, the received audio (low) is connected to pin PP of control unit connector J9101 then

through interconnecting cabling to radio set no. 2. At the control unit of radio set no. 2 these signals

become the retransmit audio and are coupled into the radio set at pins c (high) and w (low) of control

unit connector J9101.

To complete the audio path, consider radio set no. 1 (FO-18) to be in transmit condition. Transmit

audio is coupled through pins c (high) and w (low) of control unit connector J9101 to S9105C rear to

contacts 12 (high) and 6 (low). Resistor R9102 reduces the signal level for proper input to the com-

panion radio set.

Contact 12 connects to contact 10 and contact 6 connects to contact 4. From contacts 10 and 4, the

audio signal is connected through pins x (high) and d (low) of control unit connector J9101 and then

through interconnecting cabling to pins 6 (high) and 5 (low) of receiver-transmitter connector

P9601. Audio is then coupled through relay K9606, contacts 2 and 4, to pins 7 (high) and 11 (low) 0.

the amplifier-modulator for transmission.

In retransmit operation, SQUELCH control S9106 must be set to either CARR or TONE position. The

retransmit control ground, originating in the audiofrequency amplifier when a received signal causes

relay K5502 (not shown) to energize, is applied to the transmitter keying circuits of radio set no. 2

to energize the transmitter for retransmission. This ground is coupled from the audiofrequency

amplifier through pin 5 of connector P5501. The ground is then connected through pin 10 of receiver-

transmitter connector P9601, and then through the interconnecting wiring to pin Y of control unit

connector J9101.

The ground is then coupled through to SQUELCH control S9106 to contact 9 of S9105B rear. Contact 9

is connected to contact 8 in RETRAN mode, therefore, the ground is coupled out of the control unit

through pin HH of J9101. The retransmit control ground is coupled into radio set no. 2 control box at

pin u of J9101.

Assume that FO-16 now represents radio set no. 2, and that the ground is coupled through S9105A

front from contact 1 to contact 2. From contact 2, the ground is coupled out of the control unit through

pin v of J9101. The ground is then connected through interconnecting wiring to pin 41 of receiver-

transmitter connector P9601. From pin 41 of P9601, the ground is connected to the coil of relay K9602

causing it to energize which, in turn, activates the transmit circuits of radio set no. 2.

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