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Receiver VCO Q601 os cillates between
128.75 and 138.75 MHz according to model
version and the programmed receiving fre
quency. The VCO output is buffered by Q603
and returned to the 144 Mother Unit, where a
sample of that output is buffered by Q3004
(2SC4215Y) for application to the prescaler
section of Q3005. There the VCO signal is di
vided by 64 or 65, according to a control signal
from the data latch section of Q3005, before
being applied to the programmable divider
section of Q3005.
The data latch section of Q3005 also receives
serial dividing data from microprocessor
Q1005 on the Control Unit, which causes the
pre-divided VCO signal to be further divided
in the programmable divider section, de
pending upon the desired receive frequency,
so as to produce a 5-kHz or 6.25-kHz deriva
tive of the current VCO frequency. Meanwhile,
the reference divider section of Q3005 divides
the 12.8-MHz crystal reference from the 430
Mother Unit, after buffering by Q3009 (2SC-
4116GR), by 2560 (or 2048) to produce the
5-kHz (or 6.25-kHz) loop reference (respec
tively).
The 5-kHz (or 6.25-kHz) signal from the
programmable divider (derived from the
VCO) and that derived from the reference os
cillator are applied to the phase detector sec
tion of Q3005, which produces a dual 5-V
pulsed output with pulse duration depending
on the phase difference between the input sig
nals. This pulse train is filtered to DC and
returned to varactors D603 /D604 (for the tran
smitter) and D601 /D602 (for the receiver) on
the 144 VCO Unit.
Changes in the level of the DC voltage ap
plied to the varactors affect the reactance in the
tank circuit of the VCO, changing the oscillat
ing frequency of the VCO according to the
phase difference between the signals derived
from the VCO and the crystal reference oscil
lator. The VCO is thus phase-locked to the
crystal reference oscillator.
The output of receiver VCO Q601, after buf
fering by Q603, is delivered to the 144 Mother
Unit for amplification by Q3002 before appli
cation to the 1st mixer, as described previously.
For VHF transmission, transmitter VCO
Q602 oscillates between 140 and 150 MHz ac
cording to the model version and program
med transmit frequency. The remainder of the
PLL circuitry is shared with the receiver. How
ever, the dividing data from the microproces
sor is such that the VCO frequency is at the
actual transmit frequency (rather than offset
for IFs, as in the receiving case). Also, the
transmitter VCO is modulated by the speech
audio applied to D605, as described previous
ly. Receive and transmit 5-V buses select which
VCO is to be active by Q604 and Q605 (both
DTC144EE), respectively. FET Q3007 (2SK-
880GR) on the 144 Mother Unit buffers the
VCV line for application to the tracking band
pass filters in the receiver front end.
When the power saving feature is active,
the microprocessor periodically signals the
PLL IC to conserve power and shorten lock-up.
time.
UHF PLL Frequency Synthesizer
The UHF PLL circuitry consists of VCO
Q201 and VCO buffers Q202 and Q203 (all
2SC4226) on the 430 VCO Unit, and PLL sub
system IC Q2005 (MB1315PF) and 12.8-MHz
reference oscillator X2001 I Q2009 on the 430
Mother Unit. Q2005 contains a prescaler, refer
ence divider, serial-to-parallel data latch, pro
grammable divider, phase comparator, and a
power saver circuit.
For receiving, VCO Q201 oscillates between
385.225 and 405.225 MHz according to model
version and the programmed receiving fre
quency. A portion of the VCO output is buff.:.
ered by Q203 and returned to the prescaler
section of Q2005 on the 430 Mother Unit. There
the VCO signal is divided by 64 or 65, accord
ing to a control signal from the data latch sec
tion of Q2005, before being applied to the
programmable divider section of Q2005.
The data latch section of Q2005 also receives
serial dividing data from microprocessor
Q1005 on the Control Unit, which causes the
pre-divided VCO signal to be further divided
in the programmable divider section, de
pending upon the desired receive frequency,
so as to produce a 5-kHz or 6.25-kHz deriva
tive of the current VCO frequency. Meanwhile,
the reference divider section of Q2005 divides
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