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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
L1023, L1024, L1025, L1039, L1030 & L1031, capaci-
tors C1260, C1266, C1267, C1269, C1270, C1272, C1273,
C1274, C1276, C1278 & C1281 and antenna switching
diodes D1034 and D1036 (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
amplifier Q1067 (2SC5226) and varactor-tuned band-pass
filter consisting of coils L1012, L1014, L1018, L1019,
L1027 & L1028, capacitors C1209, C1211, C1212, C1217,
C1221, C1225, C1228, C1236 & C1275, and diodes
D1029, D1031, D1032 & D1040 (all HVU350), then
applied to the 1st mixer Q1068 (2SC5226).
Buffered output from the VCO is amplified by Q1030
(2SC5226) to provide a pure 1st local signal between 143.4
and 172.4 MHz for injection to the 1st mixer. The 35.4
MHz 1st mixer product then passes through monolithic
crystal filter XF1001 (35S15A, 7.5 kHz BW) which strips
away all but the desired signal, which is then amplified
by mixer postamp Q1060 (2SC4215Y).
The amplified 1st IF signal is applied to the AM/FM
IF subsystem IC Q1052 (TK10931V), which contains
the 2nd mixer, 2nd local oscillator, limiter amplifier, noise
amplifier and AM/FM detector.
A 2nd local signal is generated by PLL reference/2nd
local oscillator Q1045 (2SC4116GR) from the 17.475
MHz crystal X1002 to produce the 450 kHz 2nd IF when
mixed with the 1st IF signal within Q1052. The 2nd IF
then passes through the ceramic filter CF1001
(CFWM450D) to strip away unwanted mixer products.
In the FM mode, a 2nd IF signal from the ceramic fil-
ter CF1001 applied to the limiter amplifier section of
Q1052, which removes amplitude variations in the 450
kHz IF before detection of the speech by the ceramic dis-
criminator CD1001 (CDBM450C24). Detected audio
from Q1052 is passed through the de-emphasis, consist-
ing of the resistors R1102, R1105, R1111 & R1162, ca-
pacitors C1100, C1101, C1103 & C1145, and Q1028
(NJM2904V), then applied to the AF amplifier Q1028
(NJM2904V).
In the AM mode, detected audio from Q1052 is passed
through the audio amplifier Q1028 (NJM2904V) and
ANL circuit, then applied to the AF amplifier QQ1028
(NJM2904V). When impulse noise received, a portion of
the AM detector output signal from the AM/FM IF sub-
system Q1028, including pulse noise is rectified by
D1019 (BAS316). The resulting DC is applied to the ANL
MUTE gate Q1029 (UMG2N), thus reducing the pulse
noises.
Circuit Description
The processed audio signal from Q1028 passes
through the audio mute gate Q1016 (DTC124TU) and
the volume control to the audio power amplifier Q1009
(TDA72330), providing up to 0.4 Watts to the headphone
jack or 8 Ω loudspeaker.
A portion of the AF signal from the AM/FM IF sub-
system Q1052 converted into DC voltage within the IC,
and then passes through the AGC amplifier Q1059
(2SA1602A) and Q1062 (UMW1) to the inversion ampli-
fiers Q1063 and Q1066 (both 2SC5226). These amplifier
reduce the amplifier gain of the IF amplifier Q1060 and
the RF amplifier Q1067 while receiving a strong signal
Squelch Control
When signal is received, appear the DC squelch con-
trol voltage at pin 15 of AM/FM IF subsystem Q1052
according to the receiving signal strength. This DC is ap-
plied to pin 16 of microprocessor Q1014.
The DC squelch control voltage is compared with the
SQL threshold level by the microprocessor Q1014. If the
DC squelch control voltage is higher, pin 89 of Q1014
goes high. This signal activate the AF MUTE gate Q1016
(DTC124TU), thus disabling the AF audio.
Also, the microprocessor stops scanning, if active, and
allows audio to pass through the AF MUTE gate Q1016.
Transmit Signal Path
Speech input from the microphone is passed through
the microphone sensitivity potentiometer VR1001 and
microphone amplifier Q1005-3 (NJM2904V), then ap-
plied to the ALC amplifier Q1008 (AN6123MS). The
amplified speech signal is passed through the high-pass
filter Q1005-1 (NJM2904V) and low-pass filter Q1005-
2 (NJM2904V), then applied to the power amplifier
Q1061 (2SK2973) which AM modulate the Tx frequen-
cy with speech signal.
When using the optional headset, the SIDETONE sig-
nal from Q1011 (UMG2) becomes "HIGH," turning
Q1015 (TC7S66FU) on, therefore a portion of the speech
signal applied to the AF power amplifier Q1009 as a mon-
itor signal.
The carrier signal from the VCO Q1025 (2SC5226)
passes through the buffer amplifier Q1030 (2SC5226)
and TX/RX switch D1027 (MC2848), then amplified by
Q1047 (2SC3356) and Q1051 (2SK2973), then applied
to the power amplifier Q1061 which increases the signal
level up to 5 watts output power.
The transmit signal then passes through the antenna
switch D1034 (RLS135), and is low-pass filtered to sup-
press away harmonic spurious radiation before delivery
to the antenna.
11
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