Yaesu FT-51R, Техническое дополнение

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Description
This pulse train is filtered to DC and returned to
varactor D5001 on the 430 VCO Unit.
Changes in the level of the DC voltage applied to
the varactors affect the reactance in the tank circuit of
the VCO, changing the oscillating frequency of the
VCO according to the phase difference between the
signals derived from the VCO and the crystal refer­
ence oscillator. The VCO is thus phase-locked to the
crystal reference oscillator.
The output of VCO Q5001 is also buffered by
Q5002 & Q5003 and is then delivered to the 430
Mother Unit for amplification by Q3003 before appli­
cation to the 1st mixer, as described previously.
For UHF transmission, VCO Q5001 oscillates be­
tween 430 and 450 MHz according to the model ver­
sion and programmed transmit frequency. The
remainder of the PLL circuitry is shared with the
receiver. However, the dividing data from the micro­
processor is such that the VCO frequency is at the
actual transmit frequency (rather than offset for IFs,
FT-51R Technical Suoolement
as in the receiving case). Also, for transmission, the
VCO is modulated by the filtered speech audio ap­
plied to the tank circuit at D5003, as described pre­
viously. Receive and transmit buses select which
VCO is to be active by Q5004
(DTC143ZE),
respec­
tively. FET Q3015
(2SK880GR)
on the 430 Mother
Unit buffers the VCV line for application to the track­
ing band-pass filters in the receiver front end.
When the power saving feature is active, the mi­
croprocessor periodically signals the PLL IC to con­
serve power and shorten lock-up time.
Power-On Sequencing
Pressing the orange POWER switch applies 3 volts
to POWER SW pin 94 of microprocessor Q1002 to
wake it up. This provides 3 volts via Q1017
(XP4312)
on the Control Unit. At the same time, Q1002 pro­
vides 3 V via regulator IC Q2022 and Q2023 (both
TK
1
1230
M) on the 144 and 430 Mother Units.
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