Vertex Standard VX-820 series, Руководство по обслуживанию

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The high frequency signal components are ampli-
fied by
Q1075 (
LM2902PWR
), and their level is set
by Q1020 ( M62364FP ) to establish proper balance
of the level between high- and low-frequency com-
ponents. After that, the signals modulate the trans-
mit carrier via modulator
D1030 (
1SV286
) of the
VCO.
3-2. Drive and Final Amplifier Stages
The modulated signal from VCO Q1051 (
2SC4227
)
is buffered by Q1040 ( 2SC5005 ) and amplified by
Q1032 (
2SC5005
). Then the signal is buffered by
Q1027 ( 2SC3356 ) for delivery to the final amplifier
driver Q1024 (
2SK3475
). The low-level transmit sig-
nal is then applied to Q1019 ( 2SK3476 ) for final am-
plification up to 5 watts output power. The transmit
signal then passes through the antenna switch
D1012
(
HVU131
) and is low-pass filtered to suppress har-
monic spurious radiation before delivery to the an-
tenna.
3-3. Automatic Transmit Power Control
The current detector Q1072 ( NJM12902V ) detects
the current drawn by Q1019 ( 2SK3476 ) and Q1024
( 2SK3475 ), and converts the current difference to a
voltage difference. The output from the current de-
tector
Q1072 ( NJM12902V ) is compared with the ref-
erence voltage and amplified by the power control
amplifier
Q1072 ( NJM12902V ). The output from
Q1072 ( NJM12902V ) controls the gate bias of the fi-
nal amplifier Q1019 ( 2SK3476 ) and the driver Q1024
( 2SK3475 ). The reference voltage switches among
four values of TX Power (“High,” “Low3,” “Low2,”
and “Low1”), as controlled by
Q1020 ( M62364FP ).
3-4. PLL Frequency Synthesizer
The frequency synthesizer consists of PLL IC Q1068
( SA7025DK ), the VCO, TCXO ( X1003 ), and buffer
amplifier. The output frequency from the TCXO is
16.8 MHz, and the tolerance is ±2.5 ppm (in the tem-
perature range —30 °C to +60 °C).
3-4-1. VCO (Voltage-Controlled Oscillator)
While the radio is receiving, the RX oscillator Q1046
( 2SK508 ) in the VCO generates a programmed fre-
quency between 184.85 and 224.85 MHz as the 1st
local signal. While the radio is transmitting, the TX
Circuit Description
port) of Q1067 (CPU: LC87F5BP6A ). When a car-
rier is received, the DC voltage becomes low because
the noise is compressed. When the detected voltage
to the CPU is high, the CPU stops AF output by set-
ting
Q1083 ( DTC114TE ) “OFF” (by making pin 59
of the CPU “High” level). When the detection volt-
age is low, the CPU switches
Q1083 ( DTC114TE )
“ON” by making pin 59 “Low,” and the AF signal is
allowed to flow.
2-5-2. Carrier Squelch
The pin 15 (A/D port) of CPU Q1067 (
LC87F5BP6A
)
detects the RSSI voltage output from Q1065
(
TA31136FN
) at pin 12, and controls the AF output.
The RSSI output voltage changes according to the
signal strength of carrier; a stronger signal makes
the RSSI voltage higher. The processing of the AF
signal control is same as Noise Squelch, except that
the switching threshold is adjusted so as to be 3 dB
higher than the “tight squelch” sensitivity.
3. Transmitter System
3-1. MIC Amplifier
The AF signal from the internal microphone (pin 21
of J2002 on the Display Unit) or an external micro-
phone (pin 6 of J2002 on the Display Unit) passes
through microphone selection switch
Q2015
( CD4053BPWR ) and is amplified by microphone
amplifier Q2014 ( LM2904PWR ), thereafter passing
through the microphone gain controller, Q1020
( M62364FP ). The AF signal then passes through
compandor Q1022 ( LA8630M ). When not using the
compandor, the CPU bypasses the compandor cir-
cuit and feeds the signal to the pre-emphasis circuit.
Q1078 ( CD4066BPWR ) becomes “OFF” when an op-
tional signaling unit is attached, and the AF signal
from
Q1022 ( LA8630M ) is redirected via the signal-
ing unit. If a signaling unit is not installed, Q1078
( CD4066BPWR ) becomes “ON,” the signal bypasses
Q1078 ( CD4066BPWR ), and it instead is applied to
the pre-emphasis amplifier Q1031 ( AK2345 ). The
signal passes through the limiter and splatter filter
of
Q1031 ( AK2345 ), and is adjusted for proper de-
viation at Q1020 ( M62364FP ). The low frequency
signal components (CTCSS, DCS, etc.) are then am-
plified by
Q1075 ( LM2902PWR ) and used for direct
modulation of the reference oscillator, TCXO X1003 .