Vertex Standard VX-4100 Series, Руководство по обслуживанию, Страница: 9 / 63

1. Circuit Configuration by Frequency
The receiver is a double-conversion superheterodyne with a first
intermediate frequency (IF) of 50.85 MHz and a second IF of
450kHz. Incoming signal from the antenna is mixed with the
local signal from the VCO/PLL to produce the first IF of 50.85
MHz. This is then mixed with the 50.4 MHz second local oscil-
lator output to produce the 450 kHz second IF. This is detected
to give the demodulated signal. The transmit signal frequency
is generated by the PLL VCO, and modulated by the signal
from the microphone. It is then amplified and sent to the an-
tenna.
2. Receiver System
2-1. Front-end RF amplifier
Incoming FR signal from the antenna is delivered to the RF
Unit and passes through Low-pass filer, antenna switching di-
ode, and removed undesired frequencies by varactor diode
(tuned band-pass filer: T1001, T1002 and T1003). The passed
signal is amplified in
Q1022 (
2SC3357
) and moreover cuts an
image frequency with the band path filter and comes into the
1st mixer. The
Q1020 (
2SA1774
) controls bias of Q1022
( 2SC3357 ).
2-2. First Mixer
The 1st mixer consists of the Q1035 (
SPM5001
), T1004, T1005
and T1006. Buffered output from the VCO is amplified by
Q1038 (
2SC5226
) to provide a pure first local signal between
184.85 and 224.85 MHz for injection to the first mixer. The
output IF signal is amplified by
Q1046 (
2SC3357
) and enters
from the mixer to the crystal filter. The IF signal then passes
through monolithic crystal filters
XF1001 (±5.5 kHz BW) to
strip away all but the desired signal.
2-3. IF Amplifier
The first IF signal is amplified by Q1059 (
2SC5226
). The am-
plified first IF signal is applied to FM IF subsystem IC
Q1079
(
TA31136FN
) which contains the second mixer, second local
oscillator, limiter amplifier, noise amplifier, and S-meter am-
plifier. The signal from reference oscillator
X1003 becomes 3
times of frequencies in
Q1079
( TA31136FN ), it is mixed with
the IF signal and becomes 450 kHz. The second IF then passes
through the ceramic filter
CF1001
(for wide channels),
CF1002
(for narrow channels) to strip away unwanted mixer products,
and is applied to the limiter amplifier in
Q1038
( 2SC5226 ),
which removes amplitude variations in the 450 kHz IF, before
detection of the speech by the ceramic discriminator
CD1001
.
2-4. Audio amplifier
Detected signal from Q1079 (
TA31136FN
) is inputted to
Q1037
( AK2345 ) and is output through the band path filter
inside Q1037 (
AK2345
). When the optional unit is installed,
the
Q1063
( BU4066BCFV ) is made “OFF” and the AF signal
from Q1037 (
AK2345
) goes the optional unit. When the op-
Circuit Description
tional unit is not installed, Q1037 (
AK2345
) is made “ON”
and the signal goes through
Q1063
( BU4066BCFV ). The sig-
nal then goes through AF mute switch Q1068 (
BU4066BCFV
),
de-emphasis part and expander
Q1021
( LA8630M ). When the
function of expander is off, the 1021 will be bypassed by Q1069
( TAR5S50 ). The output signal of expander (or a signal from
de-emphasis) is amplified by Q1088 (
NJM12902V
) and it is
amplified with AF power amplifier
Q1005
( TDA1519CTH )
after passing AF volume Q1029 (
M62364FP
). The output of
Q1005
( TDA1519CTH ) drives a speaker (it chooses the exter-
nal SP or internal SP in J6001).
2-5. Squelch Circuit
There are 13 levels of squelch setting from 0 to 12. The level 0
means open the squelch. The level 1 means the threshold set-
ting level and level 11 means tight squelch. From 2 to 10 is
established in the middle of threshold and tight. The bigger fig-
ure is nearer the tight setting. The level 12 becomes setting of
carrier squelch.
2-5-1. Noise Squelch
Noise squelch circuit is composed of the band path filter of
Q1079 (
TA31136FN
), noise amplifier Q1091 (
2SC4617
), and
noise detector
D1059
,
D1061
(both DA221 ). When a carrier
isn’t received, the noise ingredient which goes out of the de-
modulator
Q1079
( TA31136FN ) is amplified in
Q1091
(
2SC4617
) through the band path filter Q1079 (
TA31136FN
),
is detected to DC voltage with
D1059
,
D1061
(both DA221 )
and is inputted to 19 pin (the A/D port) of the Q1083 (CPU:
LC87F74C8A ). When a carrier is received, the DC voltage
becomes “LOW” because the noise is compressed. When the
detected voltage to CPU is “HIGH,” the CPU stops AF output
with
Q1068 (
BU4066BCFV
) “OFF” by making the 40pin “L”
level. When the detection voltage is low, the CPU makes
Q1068
“ON” with making 40pin “H” and the AF signal is output.
2-5-2. Carrier Squelch
The pin 18 (A/D port) of
Q1083
(CPU: LC87F74C8A ) detect
RSSI voltage output from pin 12 of Q1079 (
TA31136FN
), and
controls AF output. The RSSI output voltage changes accord-
ing to the signal strength of carrier. The stronger signal makes
the RSSI voltage to be higher voltage. The process of the AF
signal control is same as Noise Squelch. The shipping data is
adjusted 3dB higher than squelch tight sensitivity.
3. Transmitter System
3-1. Mic Amplifier
The AF signal from microphone jack J4001 (4ch) or J5001
(501ch) is amplified with microphone amplifier
Q1066 , is am-
plified with 2nd microphone amplifier
Q1088
after microphone
selection switch Q1016 , and passes microphone gain volume
Q1029
. The AF signal which was controlled in the correct gain
passes compandor Q1021 . When not using a compandor, with
E-1