Yaesu FT-51R, Техническое дополнение

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Description
The FT-51R electronics consists of three major
boards: the 144 and 430 (MHz) motherboards (or
Mother Units) and the Control Unit, and numerous
minor boards that mount on these. The motherboards
include the receiver front ends, IF and PLL subsystem
ICs, and support daughter boards for transmit stages,
local VCOs, supply regulation and switching circuits.
The Control Unit includes the microprocessors and
tone generator
I
decoder chips, and supports daugh­
ter boards for the display, keys and keypad, audio
circuits and an contact board for coupling with the
motherboards. While reading this description, you
can refer to the block diagram for an overview of the
major circuit blocks, and to the schematic diagrams
for component details.
Antenna Duplexer
Incoming
RF
from the antenna jack passes through
a 450-MHz low-pass filter on the 430 Mother Unit
before application to two band-switching networks:
coil L3008, diode D3003
&
3006 and capacitor C3040
on the 430 Mother Unit for UHF signals; and coil
L2006, diode D2003 & 2007 and capacitor C2026 on
the 144 Mother Unit for VHF signals. These networks
filter VHF signals from the UHF receiver and UHF
signals from the VHF receiver, allowing each band to
operate independently while sharing the same an­
tenna connection.
VHF Reception
VHF signals passed by the duplexer are applied to
a varactor-tuned band-pass filter consisting of L2016
and L2019 before RF amplification by Q2032
(2SC4537).
The amplified
RF
is then band-pass fil­
tered again b y varactor-tuned resonators
L2015 /D2018 and L2018 to ensure pure in-band input
to 1st mixer Q2029 /D2017
(2SC4537).
Tuning volt­
age for the varactors is provided by VHF PLL Q2007,
buffered by Q2014
(2SK880GR).
Buffered 189.05
�
199.05-MHz output from the
144-VCO Unit is amplified by Q2002
(2SC4537)
and
applied to the 1st mixer. The resulting 45.05-MHz 1st
mixer product is passed through monolithic crystal
filter XF2001(± 7.5-kHz BW) to strip away all but the
desired signal, which is then amplified by Q2028
(2SC4215Y)
before delivery to FM IF subsystem IC
Q2031
(TK10930V),
containing the 2nd mixer, 2nd
local oscillator, limiter amplifier, noise amplifier, S­
meter amplifier and squelch gates. A 2nd local signal
is generated from 44.595-MHz crystal X2001, which
produces the 455-kHz 2nd IF when mixed with the 1st
IF signal within Q2031. The 2nd IF is passed through
ceramic filter CF2001 to strip away unwanted mixer
FT-51R Technical Suoolement
products, and is then applied to the limiter amp in
Q2031, which removes amplitude variations in the
455-kHz IF before detection of the speech by ceramic
discriminator CD2001. Detected audio from pin 12 of
Q2031 is delivered to the CNTL Unit.
VHF Squelch Control
When no carrier is received, noise at the output of
the detector stage in Q2031 is amplified and band­
pass filtered by the noise amp section of Q2031 and
the network between pins 19 and 20, and then recti­
fied by D2013. The resulting DC squelch control volt­
age is passed to pin 99 of Main CPU Q1002. While no
carrier is received, pin 54 of Q1002 remains low, sig­
naling pin 8 of Sub CPU Q1001
(M38223E4H P)
on the
Control Unit to keep the green (Busy) half of the VHF
LED off, and holding the AF MUTE line low to block
VHF receiver audio from passing through analog gate
Q1015-1 while no signal is being received, and during
transmission.
When a carrier appears at the discriminator, noise
is removed from the output, causing pin 54 of Q1002
to go high and signaling microprocessor Q1001 to
activate the BUSY LED. The microprocessor then
checks CTCSS chip Q1004
(AK2343)
and DTMF de­
coder chip Q1007
(TC35305F)
for CTCSS
or
DTMF
code squelch information, respectively. If not trans­
mitting and tone squelch is not activated,
or
if the
received tone matches that programmed, the micro­
processor stops scanning, if active, and allows audio
to pass through muting and amplifier IC Q1023
(TDA7233D)
to the loudspeaker.
VHF Single-Band Dual Receive
When VHF single-band dual receive operation is
active, a portion of the received VHF RF passing
through the antenna switching network (and applied
to the VHF front end) is sampled through diodes
D2006 on the 144 Mother Unit and D3007 on the 430
Mother Unit, the signals are band-pass filtered and
amplified by Q3013
(2SC4226)
before application to
mixer Q3014
(2SC4215Y).
This mixer also receives
output from the 430-VCO Unit, after it is divided by
four in Q3024
(µPB587G)
on the 430-Mother Unit.
The resulting 58.525-MHz sub-receiver 1st IF signal is
applied to the UHF receiver IF chain before mono­
lithic filter XF3001, and is then handled just as a UHF
signal would be in UHF operation.
AF Output
On the CNTL Unit, detector audio from either the
144 or 430 Mother Unit is applied through analog
switch Q1015-1 or -2
(%
NJU4066BV)
to remove the
3-1