B. Power Control and Frequency Selection
(1)
When the function switch on the remote radio set control is turned on, it provides a signal that causes a relay to energize in the power supply. The relay contacts apply the 3-phase, 115-volt, 400-Hz primary power to two bridge rectifiers. The bridge rectifiers produce +46-and +28-volt dc outputs. The +28-volt dc is used by regulators to produce +5-, +10-, +11-and +20-volt dc outputs. The +20-volt dc is routed through a relay to the receiver and switched to the transmitter exciter when the transmitter is keyed.
(2)
The operating frequency of the transceiver is selected on the remote radio set control and supplied in ARINC re-entrant code format to the frequency control. Within the frequency control, each digit of the operating frequency is decoded and converted to the bcd equivalent. The bcd frequency data is applied to a frequency band decoder and to the frequency synthesizer.
(3)
The band decoder determines which one of six bands the selected operating frequency is within, in the 2.8- to 26.999-MHz frequency range. The frequency band signal is then applied to transistor switches in the motor control. These switches apply operating voltage to the motor in the low-pass filter. The motor drives rotary switches to select one of six low-pass filters that correspond to the frequency band selected. These filters are used in the transmitter portion of the transceiver.
(4)
Within the frequency synthesizer, the bcd frequency data is applied to variable dividers in a dual phase-locked loop. The 72.6- to 96.999-MHz output signal from the vco loop is the local oscillator signal to a mixer in the receiver/exciter. The frequency synthesizer has two other output signals; a 4.5-MHz oscillator whose output is divided-by-nine. The 500-kHz signal is used with a product detector, balanced modulator, and carrier injection switch in the receiver/exciter. The 69.3-MHz signal, the seventh harmonic of the 9.9-MHz frequency standard, is used with a mixer in the receiver/exciter.
(5)
When the operating frequency is selected on the radio set control, a rechannel signal is sent to the external antenna coupler. This signal causes the antenna coupler to return to its home position. Before the transceiver can be used for communications, the antenna must be tuned to the selected operating frequency. Tuning of the antenna coupler is initiated when the key or push-to-talk (PTT) switch on the microphone is momentarily activated. During tuning, the antenna coupler supplies a tune-in-progress (TIP) signal to the transceiver and holds the key line down until tuning is complete. Within the transceiver the TIP signal produces the following results: the transmitter is placed in the AM mode with half-power output (50 watts), and the tune tone oscillator produces a 1000-Hz output to the external audio system. When tuning is complete, the TIP signal is removed from the transceiver, the coupler unkeys the transmitter, and the transceiver returns to the receive mode. With the antenna coupler tuned to the selected operating frequency, the transceiver may now be used for communications.
5C8
Jun 20/85 23-11-01 Page 7
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
(6) If the antenna coupler fails to tune properly, transmission will be inhibited. In this situation, when the key or PTT switch is activated, the KEY INTERLOCK lamp on the transceiver front panel will light to indicate an antenna coupler fault. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：737 AMM 飞机维护手册 通讯 COMMUNICATIONS(6)
