Circuit Description - Vertex Standard VXA-710 Service Manual

Receive Signal Path
Narrow FM and AM mode
Incoming RF from the antenna jack is passed through a
low-pass filter and high-pass filter consisting of coils
L1028, L1030, L1035, and L1036, capacitors C1142, C1147,
C1153, C1155, C1159, C1164, C1167, C1177, and C1221 and
antenna switching diodes D1019 (RLS135), D1020
(RN739F), and D1023 (DAN235U), and then proceeds to
the receiver front end section.
Signals within the frequency range of the transceiver are
applied to the receiver front end which contains RF am-
plifier Q1043 (2SC5555) and a varactor-tuned band-pass
filter consisting of coils L1022, L1023, L1026, L1027, L1037,
L1038, L1043, and L1044, capacitors C1130, C1134, C1135,
C1140, C1143, C1157, C1168, C1175, C1176, C1179, and
C1181, and diodes D1014, D1018, D1024, and D1026 (all
HVC350), and then applied to the 1st mixer Q1040
(2SC5555).
Buffered output from the VCO Q1014 (2SC5555) is am-
plified by Q1017 (2SC5555) to provide a pure 1st local
signal between 143.4 and 199.4 MHz for injection to the
1st mixer Q1040. The 35.4 MHz 1st mixer product then
passes through monolithic crystal filter XF1001 (35M15A1,
7.5 kHz BW) which strips away unwanted mixer prod-
uct;, the 1st IF signal is then amplified by mixer post-amp
Q1033 (2SC4215Y).
The amplified 1st IF signal is applied to the FM IF sub-
system IC Q2039 (TK10931V), which contains the 2nd mix-
er, 2nd local oscillator, limiter amplifier, noise amplifier
and FM detector.
The 2nd local signal is generated by 17.475 MHz PLL ref-
erence/2nd local oscillator X2001 (GS4613). The
17.475MHz signal is doubled by Q2036 (2SC4400) to pro-
duce the 450 kHz 2nd IF when mixed with the 1st IF sig-
nal within Q2039. The 2nd IF signal then passes through
the ceramic filter CF2002 (ALFYM450) and CF2003
(CFWM450D) to remove all but the desired signal.
In the FM mode, the 2nd IF signal from ceramic filters
CF2002 and CF2003 is applied to the limiter amplifier sec-
tion of Q2039, which removes amplitude variations in the
450 kHz IF before detection of the speech by the ceramic
discriminator CD2001 (CDBM450C24). Detected audio
from Q2039 is passed through the buffer amplifier Q2045
(NJM2125F), de-emphasis network R2101/C2077, AF
switch Q2022 (HN1J02FU), and high-pass filter Q2020-2
(NJM2904V). The processed audio signal from Q2020-2
passes through the AF MUTE gate Q2014 (DTC143ZE)
and the volume control to the audio power amplifier
Q2010 (TDA7233D), providing up to 0.4 Watts to the head-
phone jack or 8 Ω loudspeaker.

Circuit Description

In the AM mode, detected audio from Q2039 is passed
through the audio amplifier Q2020-1 (NJM2904V) and
ANL circuit, then applied to the AF amplifier Q2020-2
(NJM2904V). When impulse noise is received, a portion
of the AM detector output signal from Q2039, including
pulse noise, is rectified by D2012 (BAS316). The result-
ing DC is applied to the ANL MUTE gate Q1019 (UMG2N),
which briefly interrupts the signal flow, thus reducing the
level of the pulse noise.
The processed audio signal from Q2020-2 passes through
the AF MUTE gate Q2014 (DTC143ZE) and the volume
control to the audio power amplifier Q2010 (TDA7233D),
providing up to 0.4 Watts to the headphone jack or 8 Ω
loudspeaker.
A portion of the AF signal from the FM IF subsystem
Q2039 converted into DC voltage by D2017 (BAS316),
and then passes through the AGC amplifier Q2026
(UMW1) and Q2027 (2SA1602A) to the inversion ampli-
fiers Q1035 and Q1042 (both 2SC5555). These amplifier
reduce the amplifier gain of the IF amplifier Q1033 and
the RF amplifier Q1043 when receiving a strong signal.
Wide FM mode
Incoming RF from the antenna jack is passed through a
low-pass filter and high-pass filter consisting of coils
L1028, L1030, L1035, and L1036, capacitors C1142, C1147,
C1153, C1155, C1159, C1164, C1167, C1177, and C1221 and
antenna switching diodes D1019 (RLS135), D1020
(RN739F), and D1023 (DAN235U), and then proceeds to
the receiver front end section.
The RF signal is applied to the wide FM receiver front
end which contains RF amplifiers Q1041 and Q1046 (both
2SC5555) and a varactor-tuned band-pass filter consist-
ing of coils L1017, L1018, L1024, L1025, L1033, L1034,
L1039, and L1040, capacitors C1125, C1128, C1129, C1131,
C1136, C1148, C1158, C1162, C1163, and C1169, and di-
odes D1013, D1015, D1022, and D1025 (all HVC359), then
applied to the 1st mixer Q1039 (2SC5555).
Buffered output from the VCO Q1014 is amplified by
Q1017 (2SC5555) to provide a pure 1st local signal be-
tween 133.68 and 153.65 MHz for injection to the 1st mix-
er. The 45.65 MHz 1st mixer product then passes through
band-pass filter consisting of coils L1010 and L1011, and
capacitors C1075, C1078, C1081, C1083, C1087, and C1093.
The 1st IF signal is applied to the wide FM IF subsystem
IC Q2023 (TA7792F), which contains the 2nd mixer, 2nd
local oscillator, limiter amplifier and FM detector.
The 2nd local signal is generated by 17.475 MHz PLL ref-
erence/2nd local oscillator X2001 (GS4613). The
17.475MHz signal is doubled by Q2036 (2SC4400) to pro-
duce the 10.7 MHz 2nd IF when mixed with the 1st IF
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