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)

Resistor R9102 serves as a dropping resistor to establish the proper signal level for the transmit audio

input. The audio common in retransmit mode is connected through the front and rear wafers of switch

S9105C to the aircraft interphone amplifier.

In HOME position, the radio set provides an fm or cw homing facility which allows the pilot to home on a

signal transmitted within a frequency range of 30.00 MHz to 75.95 MHz.

When the mode control is set to HOME position, the radio set provides the operator with a visual

homing capability. Primary + 27.5 vdc power is applied the same as in the T/R mode except that + 27.5

vdc is also applied to the homer assembly to operate the homing circuits.

The homer operate voltage is coupled from contacts 9, 10, 11, and 12, of S9105D to contact 8 on the

front wafer of S9105A. in the HOME mode, contact 8 is connected to contact 7. From contact 7 of

S9105A front, the homer operate voltage is connected through pin DD of control unit connector J9101

and through the interconnecting wiring to the rf control assembly to operate communications homing

relay K4502 and other homing circuits.

When S9106 is set to CARR, the radio set receiver circuits are gated on only when the received signal

is of sufficient strength as determined by the setting of the squelch adjust (SQ ADJ) potentiometer on

the receiver-transmitter front panel.

When S9106 is set to TONE, the radio set receiver circuits are gated on only when the received signal

is modulated by a 150 Hz tone.

When SQUELCH switch S9106 is set to DIS, the ground at contact 7 is connected through S9106 to

contact 5 and then to pin V on control unit connector J9101. The ground is then connected through

interconnecting wiring and is used to energize squelch relay K5502 (not shown) in audiofrequency

amplifier assembly A5500. The squelch relay will remain energized as long as S9106 is in the DIS

position; therefore the receiver-audio amplifier will remain on and pass all audio signals.

When squelch switch S9106 is set to CARR, the ground is disconnected at contact 5 from contact 7,

and the ground applied at pin V of connector J9101 is removed. The removal of the ground deener-

gizes squelch relay K5502 in the audiofrequency amplifier assembly. This action allows the receiver-

squelch amplifier to take control of squelch relay K5502.

The noise, which is of significant amplitude in the absence of the received carrier signal, is used to

control the receiver-squelch amplifier which, in turn, operates squelch relay K5502. When a carrier

of sufficient strength is received, the noise decreases in amplitude and the receiver-squelch amplifier

energizes K5502 which, in turn, unsquelches the receiver-audio amplifier and allows the audio to

pass.

The squelch circuit can be disabled by pressing the SQ DIS button located on the receiver-transmitter

front panel. This has the same effect as switching the SQUELCH switch on the control unit to the DIS

position.

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