Alinco DR-620, Руководство по обслуживанию

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12) UHF Tx APC Circuit
A portion of the power amplifier output is rectified by D9 (M44S713), D22 (MA4S713) and Q12
(2SC4081), then delivered to APCD ICI (NJM2902V-D) as a DC voltage which is proportional to the
output level of the power amplifier.
The APC IC1 compares the rectified DC voltage from the power amplifier and the reference voltage
from the main CPU IC19, producing a control voltage for the Automatic Power Controller Q8 (RN2107)
and Q11 (RN1107) which regulates supply voltage to the Pre-Drive amplifier Q2, Drive amplifier Q1,
and Power amplifier Q4, so as to maintain stable output power under varying antenna loading conditions.
13) VHF PTT Circuit
When the PTT switch is pressed, pin 4 of front CPU IC604 (M38503M) goes “LOW,” which sends the
“PTT” command to the main CPU, IC19. When it receives the “PTT” command, pin71 of Q19 goes
“high” to control local switch D5 (DAN235E), filter switch D2, D3, TX switch D17 (DAN235E), and APC
switch Q8/Q11, which activates the VHF Tx circuit. Meanwhile, pin 69 of IC19 goes “low,” which
disables the VHF Rx circuit.
14) UHF PTT Circuit
When the PTT switch is pressed, pin 4 of FICront CPU IC604 (M38503M) goes “LO” which sends the
“PTT” command to the main CPU, IC19, When it receives the “PTT” command, pin72 of IC19 goes
“high” to controls local switch D5, filter switch D2, D3, TX switch D17 and APC switch Q8/Q11, which
activates the UHF Tx circuit. Meanwhile, pin 70 of Q19 goes “low,” which disables the UHF Rx circuit.
15) VHF PLL
A portion of the output from the VHF VCO Q9 (2SK508) passes through buffer amplifiers Q7 (2SC5066)
and Q5 (2SC5066) to the programmable divider section of the PLL IC IC2 (M64076AGP), which
divides the frequency according to the frequency dividing data from the main CPU, IC19. It is then
sent to the phase comparator.
The 21.25 MHz frequency of the reference oscillator circuit, made up of TCXO X1, is divided by the
reference frequency divider section of IC2 into 4250 or 3400 parts to become 5 kHz or 6.25 kHz
comparative reference frequencies, which are utilized by the phase comparator.
The phase comparator section of IC2 compares the phase between the frequency-divided oscillation
frequency of the VCO circuit and comparative frequency, and its output is a pulse corresponding to the
phase difference.
This pulse is integrated by the charge pump and loop filter of IC2 into a control voltage (VCV) to
control the oscillation frequency of the VHF VCO Q9.
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