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Circuit Description
2-2. Modulation
The speech input from the built-in microphone MC1001
(CZ034DP363) or external jack J1001 is pre-emphasized
by C1014 and R1021, and processed by microphone am-
plifier Q1007 (NJM12902V), IDC (instantaneous devia-
tion control) circuit to prevent over-modulation, and ac-
tive low-pass filter.
2-3. Transmission
Modulating audio passes through deviation setting D/A
converter Q1018 to MOD of the VCO. This signal is ap-
plied to diode D1021 (HSC277) in the tank circuit of VCO
Q1020 (2SC5231C8), which oscillates at the desired trans-
mitting frequency. The modulated VCO signal is buffered
by amplifier Q1021 (2SC5555) and delivered through T/
R diode switch D1024. The modulated low-level transmit
signal from the VCO is applied to amplifier Q1030
(2SC5226-5). The modulated transmit signal from the
VCO is amplified by Q1033 (RD01MUS1) and RF power
amplifier Q1039 (RD09MUP2) up to 6 W. The RF output
passes through TX diode switch D1040. RF output is
passed by T/R switch and low-pass filter to suppress har-
monics and spurious products before output to the an-
tenna at the antenna terminal.
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3. PLL Frequency Synthesizer
PLL IC Q1019 consists of a data shift register, reference
frequency divider, phase comparator, charge pump, in-
termittent operation circuit, and band selector switch. Se-
rial PLL data from the microprocessor Q1017 is convert-
ed into parallel data by the shift register in the PLL IC
Q1019 and is latched into the comparative frequency di-
vider and reference frequency divider to set a frequency
dividing ratio for each. An 11.7 MHz reference signal pro-
duced by X1001 is input to REF pin 1 of the PLL IC Q1019.
The internal reference frequency divider divides the 11.7
MHz reference by 2,340 (or 1,872) to obtain a reference
frequency of 5 kHz (or 6.25 kHz), which is applied to the
phase comparator. Meanwhile, a sample of the output of
VCO Q1021 is input to the PLL IC Q1019, where it is fre-
quency-divided by the internal comparative frequency di-
vider to produce a comparative frequency also applied to
the phase comparator. The phase comparator compares
the phase between the reference frequency and compara-
tive frequency to output a pulse corresponding to the
phase difference between them. This pulse is input to the
charge pump Q1023 (2SA1774) and Q1024 (2SC4617),
and the output from the charge pump passes through a
loop filter composed of coil L1005, resistors R1138, R1140,
& R1143, and capacitors C1106, C1109, & C1112, which
convert the pulse into a corresponding smoothed varac-
tor control voltage (VCV). The VCV is applied to varactor
D1019 and D1020 (both HVC350B) in the VCO tank cir-
cuit to eliminate phase difference between the reference
frequency and comparative frequency, and so locking the
VCO oscillation frequency to the reference crystal. The
VCO frequency is determined by the frequency-dividing
ratio sent from the microprocessor Q1017 to the PLL IC
Q1019. During receiver power save operation, the PLL
circuit operates intermittently to reduce current consump-
tion, for which the intermittent operation control circuit
reduces the lock-up time.
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