Alinco DR-620, Service Manual

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4) V/V (VHF-VHF) Dual Reception
During V & V operation, the incoming VHF “sub” band signal is passed through a low-pass filter network,
antenna switching diode D19 (1SS355), D20 (1SV268) and a high-pass filter network to the RF amplifier
Q19 (3SK131). The amplified RF signal is passed through a high-pass filter network, VHF “sub” RF
amplifier Q31 (2SC5066), and a low-pass filter network, then is applied to the VHF “sub” first mixer
Q32 (2SC5066) along with the 45.1 MHz VHF “sub” first local signal from the VHF “sub” VCO circuit.
The VHF “sub” first local signal is generated between 189.1 MHz and 193.1 MHz by the VHF “sub”
VCO Q38.
The 45.1 MHz VHF “sub” second IF signal is applied to the UHF receiving circuit. The VHF “sub” signal
is amplified, filtered, and demodulated, etc., by the UHF “main” receiving circuit, described previously.
5) U/U (UHF-UHF) Dual Reception
During U/U operation, the incoming UHF “sub” band signal is passed through high-pass and low-pass
filter networks, antenna switching diodes D16 (1SS355) and D18 (ISV268), and another high-pass
filter network to the RF amplifier Q51 (2SC5066). The amplified RF signal is passed through a low-
pass filter network, UHF “sub ”RF amplifier Q49 (2SC5066), and low-pass filter network, then is applied
to the UHF “sub” first mixer Q52 (2SC5066) along with the 21.7 MHz UHF “sub” first local signal from
the UHF “sub” VCO.
The UHF “sub” first local signal is generated between 408.3 MHz and 428.3M Hz by the UHF “sub”
VCO Q13.
The 21.7 MHz UHF “sub” second IF signal applied to VHF receiving circuit. The UHF “sub” signal is
amplified, filtered, and demodulated, etc., by the VHF receiving circuit, described previously.
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) VHF Squelch Control
When no VHF carrier is being received, noise at the output of the detector stage in IC3 is amplified and
band-pass filtered by the noise amp section of IC3, then passes through the noise adjust VR (VR8) to
CPU. The resulting DC voltage is applied to pin 88 of main CPU IC19 (M 30624FGAGP), which
compares the squelch threshold level to that which set by the font panel VHF SQL knob.
While no carrier is received, pin 55 of IC19 remains “high,” turning on the squelch switch Q108
(DTC363EK) to disable audio output from the speaker.
7) UHF Squelch Control
When no UHF carrier is being received, noise at the output of the detector stage in IC5 is amplified
and band-pass filtered by the noise amp section of IC5, then passes through the noise adjust VR8 to
cpu. The resulting DC voltage is applied to pin 90 of main CPU IC19, which compares the squelch
threshold level to that which set by the front panel UHF SQL knob.
While no carrier is received, pin 56 of IC19 remains “high” turning the squelch switch Q109 (DTC363EK)
to disable audio output from the speaker.
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