9
Receive Signal Path
Incoming RF signal from the antenna jack is delivered to
the MAIN Unit and passes through a low-pass filter con-
sisting of coils L1003 and L1006, capacitors C1009, C1012,
C1020, C1023, and C1030, and antenna switching diodes
D1006
and
D1007
(both
HSU277
).
Signals within the frequency range of the transceiver en-
ter a varactor-tuned band-pass filter consisting of coils
L1011 and L1012, capacitors C1062, C1064, C1075, C1081,
and C1084, and diodes
D1009
,
D1010
,
D1012
, and
D1013
(all
HVC355B
), then amplified by RF amplifier
Q1014
(
2SC5006
) and enter a varactor-tuned band-pass filter con-
sisting of coils L1019 and L1021, capacitors C1096, C1099,
C1108, and C1113, and diodes
D1019
,
D1020
,
D1021
, and
D1022
(all
HVC355B
), before 1st mixing by 1st mixer
Q1026
(
3SK320
).
Buffered output from the VCO
Q1003
(
2SC5231
) is am-
plified by
Q1006
(
2SC5005
) to provide a pure 1st local
signal between 194.25 and 218.25 MHz for injection to the
1st mixer
Q1026
(
3SK320
). The 44.25 MHz 1st IF signal
then passes through monolithic crystal filter XF1002 to
strip away all but the desired signal. The filtered 1st IF
signal is amplified by
Q1033
(
2SC4215Y
).
The amplified 1st IF signal is applied to FM IF subsystem
IC
Q1040
(
TA31136FN
), which contains the 2nd mixer,
2nd local oscillator, limiter amplifier, noise amplifier, and
RSSI amplifier.
A 2nd local signal is produced from the PLL reference/
2nd local oscillator of 14.60 MHz crystal X1001. The 14.60
MHz reference signal is tripled by
Q1040
(
TA31136FN
),
capacitor C1173, and coil L1030, then resulting the 43.8
MHz second local signal delivered to mixer section of
Q1040
(
TA31136FN
) which produce the 450 kHz 2nd IF
mixed with the 1st IF signal.
The 2nd IF signal passes through the ceramic filter CF1001
(for “Narrow” bandwidth channels) or CF1002 (for
“Wide” bandwidth channels) to strip away unwanted
mixer products, and is then applied to the limiter amplifi-
er in
Q1040
(
TA31136FN
), which removes amplitude vari-
ations in the 450kHz IF, before detection of the speech by
the ceramic discriminator CD1001.
Detected audio from CD1001 is applied to the audio high-
pass filter
Q1030
(
LM2902PW
), and then passes through
the AF mute switch
Q1037
(
2SA1586Y
), de-emphasis cir-
cuit consisting of resistor R1176 and Capacitor C1136, and
volume control to the audio amplifier
Q1041
(
NJM2070M
),
which provides up to 0.5 Watts to the internal 4-
Ω
loud-
speaker or the optional headphone.
Squelch Control
The squelch circuitry consists of a noise amplifier and
band-pass filter within
Q1040
(
TA31136FN
) and noise
detector
D1026
(
1SS355
).
When no carrier received, noise at the output of the de-
tector stage in
Q1040
(
TA31136FN
) is amplified and band-
pass filtered by the noise amplifier section of
Q1040
(
TA31136FN
) and the network between pins 7 and 8 of
Q1040
(
TA31136FN
), and then rectified by
D1026
(
1SS355
).
The resulting DC squelch control voltage is passed to pin
37 of the microprocessor
Q1013
(
M37516F8HP
). If no car-
rier is received, this signal causes pin 20 and 24 of
Q1013
(
M37516F8HP
) to go high. Pin 24 signal disable the sup-
ply voltage of the audio amplifier
Q1041
(
NJM2070M
).
Thus, the microprocessor blocks output from the audio
amplifier, and silences the receiver while no signal is be-
ing received (and during transmission, as well). Pin 20
signal hold the green (Busy) half of the LED
D1023
(
12-
22SURSYGC
) to off.
When a carrier appears at the discriminator, noise is re-
moved from the receiver output, causing pin 37 of
Q1013
(
M37516F8HP
) to go low and the microprocessor to acti-
vate the green (Busy) half of the LED
D1023
(
12-
22SURSYGC
) via
Q1013
(
M37516F8HP
).
The microprocessor
Q1013
(
M37516F8HP
) checks for the
CTCSS or DCS code squelch information. If the CTCSS or
DCS is not activated, or the received tone or code matches
that programmed, allows audio to pass through the au-
dio amplifier
Q1041
(
NJM2070M
) to the loudspeaker by
enabling the supply voltage to it via
Q1039
(
CPH6102
).
Transmit Signal Path
Speech input from the microphone passes through a high-
pass filter
Q1017
(
LM2902PW-2
) and AF mute switch
Q1012
(
2SA1586Y
) to
Q1001
(
M62364FP
) which adjust
the microphone gain. The adjusted audio passes through
a pre-emphasis circuit consisting of resistor R1063 and Ca-
pacitor C1074 to the limiter amplifier
Q1017
(
LM2902PW-
3
). The limited audio is applied to a low-pass filter
Q1017
(
LM2902PW-1/-4
), then return to
Q1001
(
M62364FP
)
which adjust the deviation level.
The audio signal is applied to varactor diode
D1005
(
HVC350
) which which frequency modulates the VCO
Q1003
(
2SC5231
). The modulated signal from the VCO
Q1003
(
2SC5231
) is buffered by
Q1006
(
2SC5005
), then
passes through the T/R switching diode
D1014
(
DAN235E
)
to the driver amplifier
Q1016
(
2SC5227
) and
Q1019
(
RD01MUS1
), then amplified transmit signal is applied
to the final amplifier
Q1024
(
RD07MVS1
) up to 2 watts
output power.
Circuit Description
Summary of Contents for VX-131 Series
Page 7: ...7 Block Diagram...
Page 8: ...8 Block Diagram Note...
Page 12: ...12 Circuit Description Note...
Page 20: ...20 Alignment Note...
Page 22: ...22 MAIN Unit Note...
Page 33: ...33...
