Receiver
The input signal from the antenna passes
first through a lowpass filter on the Tx
Unit, and is directed to the Rx U nit by t/r
switching diodes when receiving. On the Rx
U nit the signal is bandpas s filtered before
amplification by Q lOO l ( 2 S C3355 ) , and then
filtered by a three-stage high- Q resonator
network before application to first mixer
Q l002 ( 2 S C2026 ) . T he high-Q resonators
minimize cross modulation and intermodu
lation while providing a low noise figure
for the receiver front end . Ql002 also
receives a local signal 2 1 . 4 MHz below the
receiving frequency from VCO Q2005 ( 2 SC-
2786L ) on the Tx U nit, buffered by Q2010
( 2 SC-278 5F ) .
The 2 1 . 4 MHz product from the first mixer
is passed through 4- pole monolythic crys
tal filter XF lOOl (+/-7. 5 kHz BW) and
amplified by Q 1003 ( 2 S C535B) before appli
cation of the resulting 1st IF signal to FM
receiver sub-system IC Q 1005 (MC3361P ) ,
which contains local oscillator, mixer, I F
limiter and FM detector circuits. The ampli
fied first I F signal is applied to the mixer
section, along with the second local signal
internally generated via 20 . 945 MHz crystal
XlOOl. T he 4 5 5 kHz product, filtered by
CFlOOl, is then amplified and
limited
remove amplitude variations before appli
cation to the discriminator.
The resulting audio output from Ql005 is
delivered to the Tone U nit connector. If
no tone unit is installed, the audio is de
emphasized
by
C l034
before
passing
through VOL potentionmeter VR1002 to
audio amplifier Q 1007 (LA414 5 ) and the
loudspeaker or earphone. If a Tone U nit is
installed , resistance for the de-emphasis
network is provided on that board .
When no signal is being received, high
frequency noise is present at the output
of the discriminator stage of Q l005. T his
noise is sampled and high- pass filtered by
Rl016 and Cl025, and then amplified by a
noise amplifier in Q 1005 and Q1004 (2SC-
2603E ) , the output of which is rectified b y
Dl004/Dl005 t o provide
DC
for squelch
switching. T his squelch control DC (adj us
table by the operator via Squelch control
VRlOOl ) triggers a gate within Q l005 to
provide a squelch gate control signal
output at pin 14 .. This signal is applied to
squelch gate Ql009 ( 2 S C278 5 ) , which then
drives
Q lO lO
( 2 S B793R)
and
Q l O l l
( 2 SC278 5 ) t o turn off the supply voltage to
AF amplifier Q1007 when no signal is recei
ved . A sample of this signal also causes
TX/RX indicator LED D l006 to glow green
when the squelch is open.
Transmitter
When the push-to-talk switch is pressed,
audio from the microphone is delivered to
Mic Amp
U nit
Ql008
( DK1089 ) , which
provides audio pre-emphasis ,
me
(instan
taneous deviation control ) and low pass
filtering to prevent overdeviation from
excessive microphone levels .
Processed audio from Q lOOB is passed
through deviation trimmer VR1004 to var
actor diodes D2001 and D2002 (both 1T33)
to modulate VCO Q2005 ( 2 S C2786L ) , oscilla
ting at the transmit frequency . T he output
of Q2005 is buffered by Q2009 ( 2 SC2026)
and Q20 1 1 ( 2 S C2786L ) , and then delivered
to the three-stage RF amplifier consisting
of Q2012 ( 2 SC2407 ) , Q2013 ( 2 SC2538) and
Q2014 ( 2 SC197 1 ) , providing up 2. 5 or 4 . 5
watts R F output, depending o n the battery
voltage and High/Low power switch set
ting.
The transmit signal from final amplifier
Q20 14 is lowpass filtered by L2015/L2016,
TC2004 and C2059-206 1 , passed through t/r
switching diode D200 5, and then lowpass
filtered again by L2019 and C206 5-2067 to
suppress harmonics before application to
the antenna.
Transmit/receive switching is controlled
by Q20 19 ( BN1A4M ) , Q2020 ( BA1L4M ) and
Q2021 ( 2 S A733AP ) . When the P T T switch
lowers the impedance at the base of Q 2019,
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