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Receive Signal Path
Incoming RF from the antenna jack is passed through a
low-pass filter and high-pass filter consisting of coils
L1024, L1027, L1028, L1029, L1030 & L1031, capacitors
C1213, C1218, C1219, C1222, C1223, C1224, C1226, C1227,
C1228, C1229, C1230, & C1234 and antenna switching
diodes D1038 and D1040 (both RLS135) to the receiver
front end section.
Signals within the frequency range of the transceiver is
applied to the receiver front end which contains RF am-
plifier Q1049 (3SK318) and varactor-tuned band-pass fil-
ter consisting of coils L1014, L1015, L1018, L1021, L1025,
& L1026, capacitors C1180, C1182, C1184, C1185, C1186,
C1189, C1190, C1193, C1194, C1197, C1207, C1215, &
C1216, and diodes D1035, D1036, D1037, & D1039 (all
HVC350B), then applied to the 1st mixer Q1043 (3SK318).
Buffered output from the VCO is amplified by Q1032
(2SC5555ZD) to provide a pure 1st local signal between
155.25 and 184.25 MHz for injection to the 1st mixer. The
47.25 MHz 1st mixer product then passes through mono-
lithic crystal filter XF1001 (7.5 kHz BW) which strips away
all but the desired signal, which is then amplified by mix-
er post-amp Q1042 (2SC4915).
The amplified 1st IF signal is applied to the AM/FM IF
subsystem IC Q1039 (TK10931), which contains the 2nd
mixer, 2nd local oscillator, limiter amplifier, noise ampli-
fier and AM/FM detector.
A 2nd local signal is generated by PLL IC Q1025
(MB15A01PFV1) from the 11.7 MHz crystal X1002.
The11.7MHz signal is quadruple by Q1037 (2SC4915) to
produce the 450 kHz 2nd IF when mixed with the 1st IF
signal within Q1039 (TK10931). The 2nd IF then passes
through the ceramic filter CF1001 to strip away unwant-
ed mixer products.
In the FM mode, a 2nd IF signal from the ceramic filter
CF1001 applied to the limiter amplifier section of Q1039
(TK10931), which removes amplitude variations in the
450 kHz IF before detection of the speech by the ceramic
discriminator CD1001. Detected audio from Q1039
(TK10931) is passed through the de-emphasis, consist-
ing of the resistors R1082, R1087, R1089, & R1090, capac-
itors C1069, C1070, C1073, & C1081, and Q1019-2
(LM2902PWR).
In the AM mode, detected audio from Q1039 (TK10931)
is passed through the audio amplifier Q1019-1
(LM2902PWR) and ANL circuit, then applied to the AF
amplifier Q1019-2 (LM2902PWR). When impulse noise
received, a portion of the AM detector output signal from
the AM/FM IF subsystem Q1039 (TK10931), including
pulse noise is rectified by D1019 (1SS400). The resulting
Circuit Description
DC is applied to the ANL MUTE gate Q1022 (UMG2N),
thus reducing the pulse noises.
The processed audio signal from Q1019-1 (LM2902PWR)
is passed through the amplifier Q1019-2 (LM2902PWR)
to the volume control IC Q1029 (M62364FP). The audio
signal is passed through the volume control IC to the au-
dio power amplifier Q1003 (TDA2822), providing up to
0.7 Watts to 16 Ohm loudspeaker.
A portion of the AF signal from the AM/FM IF subsystem
Q1039 (TK10931VTL) converted into DC voltage within
the IC, and provide to the inversion amplifiers Q1048 and
Q1050 (both 2SC4617). These amplifier reduce the am-
plifier gain of the RF amplifier Q1049 (3SK318) while
receiving a strong signal.
Squelch Control
When signal is received, the DC squelch control voltage
appears at pin 15 of AM/FM IF subsystem Q1039
(TK10931) according to the receiving signal strength. This
DC is applied to pin 16 of microprocessor Q1015
(LC87F7C8A).
The DC squelch control voltage is compared with the SQL
t h r e s h o l d l e v e l b y t h e m i c r o p r o c e s s o r Q 1 0 1 5
(LC87F7C8A). If the DC squelch control voltage is lower,
the microprocessor Q1015 (LC87F7C8A) control pin 14
of volume control IC Q1029 (M62364FP) goes "LOW,"
thus disabling the AF audio. Also, the microprocessor
stops scanning, if active, and allows audio to pass through
the volume control IC Q1029 (M62364FP).
Transmit Signal Path
Speech input from the microphone is passed through the
microphone amplifier Q1011-1 (LM2902PWR), then ap-
plied to the ALC amplifier Q1013 (AN6123MS). The am-
plified speech signal is passed through the high-pass fil-
ter Q1011-4 (LM2902PWR) and low-pass filter Q1011-3
(LM2902PWR), which adjusts the modulation level, then
fed to the AM modulator Q1045 (RD07MVS1A).
When using the optional headset, pin 10 of microproces-
sor Q1015 (LC87F7C8A) goes "HIGH." This signal is
applied to pin 15 of volume control IC Q1029 (M62364FP)
which allows amplified speech signals by the AF power
amplifier Q1001 (DTC144EE) as a monitor signal.
The carrier signal from the VCO Q1028 (2SC5231) pass-
es through the buffer amplifier Q1032 (2SC5555) and TX/
RX switch D1026 (DAN222).
The signal from D1026 (DAN222) is amplified by Q1040
(2SC5226) and Q1044 (RD01MUS1), and ultimately ap-
plied to the final amplifier Q1045 (RD07MVS1A) which
increases the signal level up to 5 watts output power. The
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