CONTROL, RADIO SET C-7088/ARC-131 FUNCTIONING-continued

TM 11-5820-670-30

1-59. CONTROL, RADIO SET C-7088/ARC-131 FUNCTIONING. (CONT)

When mode control switch S9105 is set to T/R position, + 27.5 vdc from the aircraft electrical system is

applied to connector J9101 pins C, D, E, through the front and rear wafers of switch S9105D, and is

distributed to the receiver-transmitter through connector J9101 pins e, f, and F. The front wafer of

S9105C provides a path for the audio input in receive mode. The audio input signal is applied to

connector J9101 pin JJ and is fed through the front wafer of S9105C to connector J9101 pin N. The

audio output at J9101 pin N is applied to the aircraft interphone amplifier through the interconnecting

cable.

The receiver-transmitter automatically switches from receive mode to transmit operating mode when

the push-to-talk button is pressed. Pressing the push-to-talk button causes a ground signal to be

applied at connector J9101 pin q. The ground is connected through the front wafer of switch S9105A

and applied to the control coil of relay K9602 in the receiver-transmitter.

The audio signal from the operator's microphone is applied at connector J9101 pin y, connected

through the rear wafer of S9105C, and fed to the amplifier modulator assembly through connector

J9101 pin x. The audio common, in both receive and transmit mode, is connected through the front

and rear wafers of switch S9105C to the aircraft interphone amplifier.

In retransmit (RETRAN) position, the radio set operates as an automatic two-way relay which provides

communications between two other stations which are separated from each other by more than line-

of-sight range. Retransmission operation requires that two AN/ARC-131 Radio Sets or an AN/ARC-

131 and another radio set having similar capabilities, be connected back-to-back.

NOTE

In retransmit operation, the SQUELCH control must be set to either CARR or TONE posi-

tion. Retransmit operation will not function with the squelch control set to DIS.

When the mode control switch is set to RETRAN position, a ground signal is supplied by the squelch

relay in audiofrequency amplifier assembly A5500 of the receiving radio set to the control units of the

two radio sets. The ground signal is applied to connector J9101 pin Y and connected through the front

wafer of SQUELCH switch S9106 to the rear wafer of S9105B. Switch S9105B in turn applies the ground

to pin HH of connector J9101.

Through the interconnecting of the two control units, the ground at J9101 pin HH is fed to pin u of

connector J9101 on the control unit of the transmitting radio set and is connected to J9101 pin v,

through the front wafer of switch S9105A. This ground is used to key the transmitting radio set. By

using the squelch relay of the receiving radio set, a ground is not provided to the transmitting set until

a signal is received at the receiving radio set. When the transmitting set is keyed, the ground to its

squelch relay is broken, and prevents lockup of both radio sets in transmit mode.

In retransmit mode, received audio signals are applied to the control unit of the receiving radio set at

connector J9101 pin JJ and passed through the front wafer of switch S9105C to pins N and A of J9101.

The audio at pin N is sent to the aircraft interphone amplifier and can be monitored by the operator.

The audio at pin A is applied to connector J9101 pin c in the control unit of the transmitting radio set.

The rear wafer of switch S9105C connects the audio for retransmission to the amplifier modulator

assembly through pin x of J9101.

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