1_ SSB mode
 Whatever the signal received, USB or LSB, the 500 KHz signal
 obtained from the transformation of the previous frequencies
 is always a LSB signal.
 This signal is filtered, amplified and then applied to a mixer
 detector. 

R 1EFF : 051-099, 106-149, 201-299, 301-399, 1 23-11-00Page 31 1401-499, 1Aug 01/05 1 1 1CES 1

 Transceiver Power Supply - Block Diagram
 Figure 007

R 1EFF : 051-099, 106-149, 201-299, 301-399, 1 23-11-00Page 32 1401-499, 1Aug 01/05 1 1 1CES 1

 HF Transceiver - Receive Mode - Block Diagram
 Figure 008

R 1EFF : 051-099, 106-149, 201-299, 301-399, 1 23-11-00Page 33 1401-499, 1Aug 01/05 1 1 1CES 1 The mixer detector receives the LSB signal of 500 KHz and the square wave signal of 500 KHz from the synthesizer. The output is the detected audio signal. This signal is amplified and fed to the AGC and AF input circuit which receives signal from the AM and SSB channels. The AF input circuit supplies the audio output and the DATA output through a final amplifier controlled by a squelch circuit.

 2 AM mode
_ The 500 KHz signal from the second mixer is filtered and amplified. This amplified signal is transmitted to the AGC circuit and to the AF circuits. At audio output, the signal is fed to the AF input circuit described above.
 (d) Transmitter (Ref. Fig. 009) The modulation signal (audio, data) is supplied to a compressor/ amplifier. The audio signal is modulated into a modulator balanced by an injection signal of 500 KHz from a frequency synthesizer. The 500 KHz carrier is cancelled and the two sidebands only remain at modulator output. A first amplifier amplifies the signal. Then the signal is applied to a Lower Side Band (LSB) mechanical filter. The filter removes the Upper Side Band (USB). The signal is then amplified in a second 500 KHz amplifier before it is applied to a first mixer. When transmitted in AM mode, the second 500 KHz amplifier receives a 500 KHz carrier signal from the synthesizer. The 500 KHz signal, with or without a carrier, is then mixed in a mixer with a signal of 69.3 MHz in USB mode and a signal of 70.3 MHz in LSB mode. These signals from the frequency synthesizer produce a signal of
 69.8 MHz frequency by beating with the 500 KHz signal of the
 lower band.
 The 69.8 MHz frequency signal is fed to a second mixer through a
 crystal filter.
 Within the second mixer, the 69.8 MHz signal is mixed with a
 frequency signal between 71.8 MHz and 99.7999 MHz from the
 synthesizer.
 The resulting signal is between 2 and 29.9999 MHz.
 This output signal is amplified, then filtered.
 An attenuator, controlled by an automatic load control (ALC)
 system, maintains constant the signal output level.

R 1EFF : 051-099, 106-149, 201-299, 301-399, 1 23-11-00Page 34 1401-499, 1Aug 01/05 1 1 1CES 1

 HF Transceiver - Transmit Mode - Block Diagram
 Figure 009

R 1EFF : 051-099, 106-149, 201-299, 301-399, 1 23-11-00Page 35 1401-499, 1Aug 01/05 1 1 1CES 1 This signal is then applied to a four-stage power amplifier which raises the power to 400 W, peak-to-peak. The power amplifier stage has protective circuits which provide instantaneous reduction of the output power in the event of component overload or overheating. The signal is routed through seven filters which can be switched in by a motor, according to the useful frequency. These filters cover the frequency band from 2 to 29.999 MHz and remove the harmonics of the useful frequency. The signal is then transmitted to the antenna coupler and antenna through an antenna relay and internal directional wattmeter. Transmitted and reflected power measured by the wattmeter generates a voltage. The voltage is used for modulation control, automatic load control (ALC) attenuator and power amplifier protection.

 (e) Synthesizer (Ref. Fig. 010) The frequency synthesizer provides three frequency signals:
 -
a variable frequency sine wave between 71.8 and 99.7999 MHz

 -
a fixed frequency square wave of 500 KHz

 -
a USB 69.3 MHz sine wave or a LSB 70.3 MHz sine wave signal. The signals are generated from a 9.9 MHz frequency standard.

 1_ 500 KHz signal
 A 9.9 MHz crystal oscillator generates the 500 KHz signal. The
 signal is then divided. A monitoring circuit compares the
 signal from the crystal oscillator with the frequency standard
 in order to obtain a great stability.
 The 500 KHz signal is used in the balanced modulator and in
 the mixer detector used in SSB reception.
 2_ 69.3 MHz (USB) and 70.3 MHz (LSB) signals
 A 69.3 or 70.3 MHz voltage-controlled oscillator (VCO)
　
中國航空網 m.k6050.com
航空翻譯 www.aviation.cn
本文鏈接地址：A320飛機維護手冊 AMM Communications 通訊1(45)