Alinco DJ-V57, Service Manual

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DJ-V57 CIRCUIT DESCRIPTION
[Reception]
1. RX Method: Double Conversion Super Heterodyne
1st IF: 38.85 MHz
2nd IF: 450 KHz
2. Front End
[VHF]
The signal input from antenna passes through the low pass filter, and then it is
amplified at RF amplifier Q117. The amplified signal is led to band pass filter
and band switch D132, then input to the mixer Q120.
[UHF]
The signal input from antenna passes through the high pass filter and low pass
filter, and then it is amplified at RF amplifier Q123. The amplified signal is led
to band pass filter and band switch D132, then input to the mixer Q120.
3. Mixer
The input signal to the mixer Q120 and the 1st local signal are added or
subtracted at the mixer Q120, and the crystal filter XF101 selects the signal of
38.85 MHz, then it is amplified at the 1st IF amplifier Q121 after the adjacent
signal is eliminated. The 1st local signal from VCO output is supplied to the
base of mixer Q120 passing through the buffer amplifier Q116.
4. IF
The signal amplified at the 1st IF amplifier Q121 is supplied to pin 16 of IC105
for demodulation. Also the signal of 12.8 MHz from X101 multiplied by three at
Q115, and then it is led to pin 1 of IC105. Two input signals are mixed in the
mixer circuit inside of IC105 and converted into the 2nd IF signal of 450 kHz.
The 2nd IF signal output from pin 3 of IC105 is supplied to pin 5 of IC105 after
eliminating the adjacent signal at the ceramic filter CF101 in WFM mode, or at
the ceramic filter CF102 in NFM mode. The input 2nd IF signal to pin 5 of
IC105 is demodulated at the limiter amplifier and quadrature detection circuit
inside of IC105, then output from pin 9 of IC105 as an AF signal.