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Ci rcu i t Descr i ption
Q1011 (MX265LH) and DTMF decoder chip
Q1008 (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 microprocessor stops scanning, if active,
and allows audio to pass through muting gate
Q1406 to the amplifier and loudspeaker.
VHF Single-Band Dual Receive
When VHF single-band dual receive opera
tion is active, a portion of the received VHF
passing through the antenna switching net
work (and applied to the VHF front end) is
sampled through diodes D3005 on the 144
Mother Unit and D2027 on the 430 Mother
Unit, for delivery to the V /V
board on the 430 Mother Unit. On this daugh
ter board, the signals are band-pass filtered
and amplified by Q5002 (2SK882Y) before ap
plication to mixer Q5001 (2SC4215Y). This
mixer also receives output from the 430-MHz
VCO Unit, after it is divided by four in Q4002
(µPB587G) on the V /V Local Unit. The result
ing 44.775-MHz sub-receiver 1 st IF signal
(V /V IF) is applied to the UHF receiver IF
chain before monolithic filter XF2002, and is
then handled just as a UHF signal would be in
operation.
UHF
AF Output
On the MIC/ AF Amp Unit, detector audio
from either the 144 or 430 Mother Unit is a
plied through analog switch Q1406-3 or -4 ( Yt!
NJU4066BW) to high-pass filter Q1403-4 or -3
(Y4
LM324DB), respectively, which removes
the CTCSS tone, if present, and adds keypad
beeps and DTMF monitor tones as needed via
Q1403-2. The resulting audio is delivered
through the respective volume control and
audio selector Q1 705 (µPD4052BG) on the
Volume Unit, which selects VHF and UHF
audio on the internal or external (EAR jack)
loudspeakers, separate or mixed, through
dual audio amplifier Q1401 (NJM2073D) on
the Mic/ AF Amp Unit. When no e xternal
loudspeaker is connected, D1402 signals the
microprocessor to cause audio selector Q1 705
to mix both channels of audio together for the
internal loudspeaker.
RF
Unit daughter
Rx
f
UHF Reception
UHF signals passed by the duplexer are
applied to a varactor-tuned band-pass filter
consisting of L2015 and D201 7 /D2021 before
amplification by Q201 6 (2SC4325). The
RF
amplified
RF
is then band-pass filtered again
by varactor-tuned resonators L2018 /D201 6 I -
D2020 and L2017 /D2015/D201 9, further am
plified by Q2015 (2SC4325) and filtered once
more by L2016/D2014/D2018 to ensure pure
in-band input to 1 st mixer Q2012 (2SC4537).
Tuning voltage for the varactors is provided
by UHF PLL Q2005, buffered by Q2007 (2SK-
880GR).
Buffered
output between 385 .225 and
405.225-MHz from the VCO Unit is amplified
by Q2002 (2SC4227-R32) and applied to the
1 st mixer. The resulting 44.775-MHz 1 st mixer
product is passed through dual monolithic
crystal filters XF2001 /XF2002 (± 7.5-kHz BW)
to strip away all but the desired signal, which
is then amplified by Q2013 (2SC4215Y) before
delivery to
IF subsystem IC Q2011 (MC-
FM
33720), which contains the 2nd mixer, 2nd
local oscillator, limiter amplifier, noise ampli
fier, S-meter amplifier and squelch gates.
A 2nd local signal is generated from 45.23-
MHz crystal X2002, which produces the 455-
kHz 2nd IF when mixed with the 1 st IF signal
within Q2011 . The 2nd IF is passed through
ceramic filter CF7001 on the IF Unit daughter
board to strip away unwanted mixer products,
and is then applied to the limiter amp in
Q2011, which removes amplitude variations in
the 455-kHz IF before detection of the speech
by ceramic discriminator CD7001, also on the
daughter board.
Detected audio from pin 9 of Q2011 is de
emphasized and delivered via the 430 Mother
Unit, Interface Unit and Control Unit (for sam
pling by CTCSS & DTMF detectors), to the
MIC/
Amp Unit. Receiver audio amplifica
AF
tion is as already described.
UHF Squelch Control
When no carrier is received, noise at the
output of the detector stage in Q2011 is ampli
fied and band-pass filtered by the noise amp
section of Q2011 and the network between
pins 9 and 1 0, and then rectified by D2012. The
resulting DC squelch control voltage, adjusted
/
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