TRANSMIT OPERATION.

TM 11-5820-670-12

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GENERAL. (CONT)

Operation of the radio set is entirely remote controlled. Manual selection of any of the 920 channels is

accomplished by rotation of four frequency selector switches on the control unit. Motors in the

receiver-transmitter automatically tune the radio set to the frequency setting on the control unit.

NOTE

The following frequencies cause transmitter quieting of the receiver and must not be

used during testing, alinement, or operation; 33.90 MHz, 45.20 MHz, 56.50 MHz, and

67.80 MHz.

When configured properly, the radio set is capable of the following operations; transmit, receive,

homing, and retransmit.

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TRANSMIT OPERATION.

During transmit operations, audio signals generated by the microphone are routed to the receiver-

transmitter through the aircraft interphone amplifier (intercommunications control set) and control

unit. In the receiver-transmitter, the audio signal is converted to a rf signal. The rf signal is then

routed to the communications antenna which radiates the signal.

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RECEIVE OPERATION.

During receive operations, an fm communications signal is intercepted by the communications or

homing antenna and routed to the receiver-transmitter. In the receiver-transmitter, the fm signal is

amplified and converted to an audio signal. The audio signal is fed through an audio preamplifier and a

power amplifier in the intercommunication control set to the control unit. From the control unit, the

audio signal is fed through the aircraft interphone amplifier to the headset-microphone.

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HOMING OPERATION.

During homing operations, homing signals, which can be fm or unmodulated, are intercepted by a

controlled-pattern antenna system and coupled to the receiver-transmitter. The homing circuit in the

receiver-transmitter alternately samples the signal from one then the other antenna at a 100 Hz rate,

giving the resultant signal two components. When aircraft leading is alined with the transmitting

station, the signal components have the same signal strength. However, when the aircraft heading is

to either side of the transmitting station, the signal strength of one component is stronger or weaker

than the other. This information is sent to the aircraft homing indicator vertical pointer which provides

a visual indication of aircraft heading, with respect to the transmitting station. Over-the-station

homing is indicated by the homing indicator horizontal pointer which rises as signal strength

increases. Maximum signal strength is indicated when horizontal pointer is center scale (horizontal).

NOTE

A flag alarm system is provided on the homing indicator to indicate that the homing

signal is of sufficient strength. When the flags are not visible, there is sufficient signal

strength; when the flags are visible, the homing signal is too weak to provide proper

homing information.

The radio set is still capable of two-way communications operation while the control unit

mode selector switch is set to HOME, and homing operations are being preformed,

However, homing is temporarily interrupted during a transmit operation.

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