(b) Not Applicable
R **ON A/C 051-099, 106-149, 201-299, 301-399, 401-499,
The VHF transceiver ensures its primary functions through :
-
the receiver
-
the transmitter
-
the synthesizer The antenna switch and final filter assembly:
-route the input signal from the antenna to the receiver in the receive mode
-connect the transmitter RF output to the antenna in the transmit mode.
(a) Receive Mode The signal is applied through a transmit/receive switch to a hight-pass filter on the RF assembly that rejects signals in the the FM broadcast band. RF is then applied through an attenuator which reduces high level signals to prevent cross-modulation effects and spurious responses. The signal is then filtered by two varactors-tuned filters and an RF amplifier which provides 80dB rejection to image frequencies. Tuning voltage is provided by d/a converters on the system processor.
R 1EFF : 001-049, 051-099, 101-149, 201-299, 1 23-12-00Page 27 1301-399, 401-499, 1Aug 01/05 1 1 1CES 1 A passive mixer converts the 118 - 138Mhz signals with a +20-dBm synthesiser frequency from the signal processor to a 20.125Mhz if frequency. Anolog AGC is provided for IF and RF amplifiers by op-amp integrator circuits. The AM baseband input from the RF assembly is low-pass filtered by an analog filter, applied to a 12-bit A/D converter, and sampled at 84kHz. The signal is amplitude compressed so that modulation levels over a 6dB range provided the same output level. The signal is digitally filtered to provide a -3dB response of 300 to 2500 hZ. The signal also has the capability of being muted at least 80 dB. A squelch decision logic function that monitors the inputs from the AGC and noise squelch is used to remove muting from the receive audio when the signal strengh is above a certain level. These are dc levels that vary in proportion to signal strengh.
(b) Transmit mode The input from the microphone inputs is low-pass filtered by an analog filter, applied to a 12-bit A/D converter, and sampled at 84 kHz. The signal is amplitude compressed so that modulation levels over a 20 dB range provide the same output level. The compressor treshold level is sofware selectable via commands from the system processor. The signal is digitally filtered to provide a -3dB response of 300 to 2500Hz. The sidetone audio output signal is amplified to a nominal 10 mW level and routed to the rear connector. A +20-dBM signal is applied from the signal processor to a QAM modulator. Proper phase shift for the I and Q modulators is adjustable by a voltage from the system processor providing optimun phase shift at all VHF band frequencies. The baseband I and Q channels from the signal processor are applied to the balanced modulators and summed to provide the QAM function. The modulator signal is amplified to the +20-dB level and sampled by the phase correcting loop. The main path of the signal is applied to a phase correcting element and an amplitude adjusting element. The signal is then amplified by a four linear power amplifier to +51-dBm peak level. A pre-tuned low-pass filter reduces the harmonic level to better than -60 dB. A 20 dB dual directional coupler provides samples of incident and reflected power for linear diode detectors. A T/R switch outputs the transmitter to the main antenna. Baseband feedback is used for both phase and amplitude components of modulation signal.
R 1EFF : 051-099, 106-149, 201-299, 301-399, 1 23-12-00Page 28 1401-499, 1Aug 01/05 1 1 1CES 1 **ON A/C 151-199,
(a)
General operation The VHF transceiver ensures its primary functions through:
-RF module
-Main processor module
-Power supply module
-HIRF/Rear interconnect
-Front panel display assembly
-Memory card interface module.
(b)
Not Applicable
**ON A/C 001-049, 101-105,
(c) Power supply (Ref. Fig. 007) The 27.5VDC input is filtered for direct use in the transmitter. A 15 V regulator and a 8 V regulator provide the operating voltage for other sub-assemblies. The output is fully protected against all overload and short circuit conditions.
R **ON A/C 051-099, 106-149, 201-299, 301-399, 401-499,
(c) Power supply The power supply provides four voltages to the tranceiver +12 Vdc, -12 Vdc, +35 Vdc, and 5Vdc. The power supply will be shut down by over/undervoltage circuits when the input voltage is not within limits. The power supply monitor a power supply over/under voltage output to the system processor. Energy-storage circuits provide operation during input power interrups of 200 msec or less.
**ON A/C 001-049, 101-105,
(d)
Receiver
(e)
Transmitter (Ref. Fig. 008) The transmitter receives the input RF excitation from the frequency synthesizer.
1EFF : ALL 1 23-12-00Page 29 1 1 Aug 01/05 1 1 1CES 1
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：A320飞机维护手册 AMM Communications 通讯1(69)
