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- - - - - - - - - - - - - - - - C i r c u i t Description
~Receive
Signal Path
Incoming RF from the antenna jack is deliv-
ered to the PA Unit and passes through a low-
pass filter consisting of coils L703
&
L704,
capacitors C712
&
C713 and antenna switching
diodes, D703
&
D704 (both Ml308) to the
MAll\i l.Jnit. Signals within the trequency
range of the transceiver then enter a varactor-
tuned band pass filter consisting of diode
D1012 (1 T326) & T1005 before RF amplifica-
tion by Q1004 (3SK131). The amplified RF is
then varactor-tuned band pass filtered again by
diodes D1005, D1006, D1007 & D1008 (all
1 T362) and T1003, T1004, T1006
&
T1007 be-
fore impedance matching by T1001 and enter-
~ing
the 1st mixer Q1001
&
Q1003 (both
2SK302).
Buffered output from the VCO Unit is am-
plified by Q1011 (2SC2759)
to
provide a pure
1st local signal between 126.3 and 130.3MHz
for injection
to
the 1st mixer. The 17.7-MHz 1st
mixer product then passes through dual mono-
lithic crystal filters XF1001
&
XF1002 (both
17T15BU: ± 7.5 kHz BW)
to
strip away all but
the desired signal, which is then amplified by
Q1002 (2SC2620).
The amplified 1st IF signal is applied to FM
IF subsystemIC Q201 (MC3372ML) on the IF
Unit, which contains the 2nd mixer, 2nd local
oscillator, limiter amplifier, noise amplifier, S-
,-.,meter amplifier and squelch gates. A 2nd local
signal
is
generated from 17.245MHz crystal
X201, to produce the 455kHz 2nd IF when
mixed with the 1st IF signal within Q201. The
2nd IF then passes through ceramic filter CF
1001 (CFW455E) on the MAIN Unit,
to
strip
away unwanted mixer products, and is then
returned to the IF Unit and applied
to
the
limiter amplifier in Q201, which removes am-
plitude variations in the 455kHz IF, before de-
tection of the speech by ceramic discriminator
CD201 (CDB455C7).
Detected audio from Q201 is fed through
mute analog switch Q906 (2SC2812) on the
MUTE Unit and then enters the MIC AMP
UNIT for de-emphasis, high-and low- pass fil-
tering by Q501 (NJM2902M-1, -3) on the MIC-
AMP Unit before returning
to
the MAIN Unit.
Audio output level is controlled by VOL poten-
tiometer VR2002 on the CNTL Unit and audio
amplifier Q1020 (AN5262) before application
to audio power amplifier Q1021 (TDA2003) for
up to 2 watts for the optional headphone jack
or 8-ohm loudspeaker.
Squelch Control
The squelch circuitry consists of a noise am-
plifier, high-pass filter
&
squelch trigger within
Q201, and noise detector D201 (1 SS302), both
on the IF Unit, squelch gate Q506 on the MIC-
AMP Unit, and control circuitry within micro-
processor Q2001 (HD4074629H) on the CNTL
Unit.
When no carrier is received, noise at the
output of the detector stage of Q201 (pin 11) is
detected by D201 (1 SS302) to provide a DC
control voltage for squelch gate control. This
voltage is delivered to NOISE/I-I TEMP pin 2
of Q2001 on the CNTL Unit. With no carrier
present, pin 2 of Q2001
is
high which signals
the microprocessor
to
activate squelch gate
Q506 (DTC323TK) on the MIC-AMP Unit,
pulling the audio line
to
ground, thus silencing
the receiver while no signal
is
being received.
Transmit Signal Path
Speech input from the microphone is deliv-
ered via the CNTL Unit to the MIC-AMP Unit,
where it passes through Mic Amplifier Q501
(NJM2902M-4) and Mic Mute analog switch
Q503 (UPD4052BG). To prevent over-devia-
tion, the audio is processed by IDC (instantane-
ous deviation control) Q501 (NJM2902M-2),
and then low-pass filtered by Q501
(NJM2902M-3) before delivery to the modula-
tor on the VCO Unit.
If a CTCSS tone is enabled for transmission,
the subaudible tone from microprocessor
Q2001 on the Control Unit is lowpass filtered
-------------------~--------------------------~---------1-7
FT-2200 Technical Supplement
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