Benison V7, Руководство по обслуживанию

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V7
3
CIRCUIT DESCRIPTION
1. Frequency configuration
The receiver utilizes double conversion. The first IF is 38.85MHz and the second IF is
450kHz. The first local oscillator signal is supplied from the PLL circuit. The PLL circuit in
the transmitter generates the ecessary frequencies. Fig. 1 shows the frequencies.
2. Receiver
The freauency configuration of the receiver is shown in Fig.2.
1) Front - end RF amplifier
An incoming signal from the antenna is applied to an RF amplifier (T201) after passing
through a transmit/receive switch circuit (D101 ,D102,D103) and a 3-pole LC
filter(L203,L204).After the signal is amplified (T201), the signal is filtered by a band pass
filter (a 3-pole LC filter) (L217,L218,L221) to eliminate unwanted signals before it is
passed to the first mixer. The voltage of these diodes are controlled by to track the
MPU(U811) center frequency of the band pass filter. (See Fig. 2)