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 a bridge rectifier. The bridge rectifier produces -12-, +5-, +10-, +20-, +27.5- and +50-volt dc outputs.
(2)
The operating frequency of the transceiver is selected on the remote radio set control and supplied in ARINC reentrant 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 routine determines which band the selected operating frequency is within, in the 2.000- to 29.999-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 the low-pass filter 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 71.8- to 99.7999-MHz output signal from the vco loop is the local oscillator signal to a mixer in the receiver/exciter. The frequency synthesizer has three output signals; a 19.8-kHz, a 69.3/70.3-MHz, and a 500-kHz signal. The 69.3- and 70.3-MHz frequencies are generated by VCO's which are phase-locked to a 100-kHz reference derived from the 9.9-MHz frequency standard.
(5)
When the operating frequency is selected on the radio set control, a rechannel signal is sent to the 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 low power output (72 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.
(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.
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23-11-02 Page 6 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Jun 20/85
C. Transmit Mode
(1)
In transmit mode, the transceiver will produce nominally 400 watts PEP RF output in SSB operations and a nominal 125 watts average RF output in AME operation. Both voice and data audio signals may be used to modulate the RF carrier.
(2)
When the key or PTT switch on the microphone is activated, a relay in the power supply switches +20-volt dc power to the transmitter circuits in the receiver/exciter. The key-line or (PTT) signal is also applied to a transistor switch that enables the audio amplifier. The audio amplifier, whose gain is controlled by a compression amplifier, supplies a constant audio peak voltage output to a balanced modulator. The constant optimum audio level reduces the intermodulation products generated in the modulator. A part of the audio output from the audio amplifier is the sidetone signal. Thus, the audio being used to modulate the transmitter can be heard on the audio output system.
(3)
Within the balanced modulator, the audio signal modulates the 500-kHz injection signal from the frequency synthesizer. The double-sideband suppressed carrier 500-kHz output of the modulator is attenuated in AM mode by an electronic switch before being applied to a lower sideband (LSB) mechanical filter. The filter removes the upper sideband (USB) and 500-kHz carrier passing only the lower sideband. Another IF amplifier then amplifies the LSB signal to a level adequate to drive the first mixer of the up-converting frequency translator. When transmitting in AM mode, this IF amplifier also receives a 500-kHz carrier signal, from the frequency synthesizer through a carrier injection switch.
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