Alinco DJ-596E, Руководство по обслуживанию

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4
5. Squelch
Q24 determines the gain of AF signal output from pin 12 of IC5 according to
the WFM/NFM of IC8. Then the signal is input to pin 19 of IC5. The input signal
passes through the noise filter amplifier and rectifier circuit, then output from
pin 21 of IC5. The output signal is supplied to A/D port of microprocessor IC6,
then the microprocessor IC6 judges it to control ON/OFF of the audio output.
6. Audio
Q24 determines the gain of AF signal output from pin 12 of IC5 according
to the WFM/NFM of IC8. Thereby amplified signal passes through AF switch
IC15 and band pass active filter IC8, then controls AF signal level at the
microprocessor IC6 with the electronic volume IC10. The controlled AF signal
is supplied to the audio power amplifier IC9 pin 2. The input AF signal is
amplified at IC9 and output from pin 6 to drive the speaker, etc.
7. VCO
VHF
VCO in VHF band consists of the Colpitts oscillator. D6, D9, L15 and L20
determine the oscillating frequency, and the signal is oscillated at the transis-
tor Q4. L20 is passed at shift transistor Q8 when receiving. The oscillated
signal is supplied to pin 2 of PLL-IC2 passing through the buffer amplifier Q7
and Q1.
UHF
VCO in UHF band consists of the Colpitts oscillator. D16, D18 and L22
determine the oscillating frequency, and the signal is oscillated at the transis-
tor Q12. The oscillated signal is supplied to pin 19 of PLL-IC2 passing through
the buffer amplifier Q7 and Q1.
8. PLL
PLL-IC2 is used to control the oscillating frequency of VCO. IC2 is controlled
by the serial control signal sent from the microprocessor IC6. The refer-
ence frequency of 12.9 MHz from IC2 oscillates the crystal oscillator X1 in-
side the circuit.
VHF
IC2 compares the frequency gained by dividing the signal added to pin 2 of
IC2 by the control signal from IC6 with the frequency gained by dividing
the reference frequency of 12.9 MHz inside IC2. When the phase difference
is found as a result of phase comparison, the pulse signal is output from the
charge pump output of pin 8 of IC2, then the signal is converted into the DC
voltage at the passive filter and added to the cathode side of VCO vari-cap D6
and D9 to make the phases equal. In result the stabilized oscillation can be
done at the desired frequency.