Vertex Standard VXA-200, Руководство по обслуживанию

Страница: 7 / 28

7
Circuit Description
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
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