TRANSMITTER KEYING CIRCUITS-continued

TM 11-5820-670-30

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

In transmit operation, the control unit control switch is placed in T/R position as shown in FO-14.

Input voltage, +27.5 vdc, is supplied by the aircraft electrical system and is applied to the radio set

through connectors J9101 pin D, S9105 C, J9101 pin F, main connector P9801 pin 36, and connector

P9501 pin 9 to the power supply.

Application of +27.5 vdc activates the power supply. Upon being activated, the power supply applies

+24 vdc to the vhf tuner, gearbox, audio amplifier, voltage regulator, and relay K9605. It also supplies

+ 27.5 vdc to relays K9601, K9602, K9803, K9604, and K9606.

The transmit command (ground signal) from the push-to-talk button is applied through connector

J9101 pin q, switch S9105A, back through connector J9101 pin v of the control unit, to main con-

nector P9601 pin 41 and K9602 pin 3. Upon receipt of the transmit command, K9602 energizes and

removes the receive mode ground from contact 8 and applies a ground through contacts 2 and 5 to the

power supply. The application of the ground starts the power supply blower motor used for cooling

during transmit mode.

The transmit mode ground is also applied through contacts 6 and 1 of K9602 to the rf control assembly,

audio amplifier, and relays K9601 contact 3, K9603 contact 3, and K9604 contact 3. The transmit

mode ground is obtained through contacts B2 and B3 of K9605. Relay K9605 energizes only when the

radio set is tuning. Application of the transmit ground causes relays K9601, K9603, and K9604 to

energize simultaneously.

When K9601 is energized, +24 vdc from the power supply is connected through contacts 2, 5, and 6,

1, of K9601 to activate the rf amplifier.

When K9603 is energized, + 105 vdc plate voltage for the vhf tuner is removed and contacts 1 and 6

apply a ground to the plate circuit. The voltage regulator assembly applies + 16 vdc through contacts

2 and 5 of K9603 and through connector P8701 pin 10 to turn on the amplifier modulator assembly,

transmit section of the vhf tuner, oscillator and buffer amplifier, and the isolation amplifier.

When K9604 is energized, connectors P2101 pin 2 and P2101 pin 3 of the voltage regulator are tied

together through contacts 5 and 2 of the relay. This action enables the squelch delay circuit by dis-

charging C2101 through contacts 2 and 5.

The transmitter dc control voltage from the if. amplifier hunt cutoff detector is applied through con-

tacts 1 and 6, R9601 and CR9606 to the amplifier modulator assembly. The transmitter dc control

voltage is used to disable the hunt generator when the master oscillator has reached the correct fre-

quency. In receive mode of operation, the transmitter dc control voltage is disconnected and one end

of R9601 is grounded through contacts 6 and 8 of K9604, discharging C9601.

During transmit mode operation, the audiofrequency amplifier supplies a 150 Hz tone signal. The tone

is applied through connector P5501 pin 1, contacts 6 and 8 of dummy relay K9606, and connector

P8701 pin 8 to the amplifier modulator. The transmitter audio input from the aircraft interphone ampli-

fier is applied to the amplifier-modulator through contacts 2 and 4 of K9606. In wide band operation,

the tone signal is also interrupted by the wideband mode ground applied through diode CR9603.

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