Vertex Standard VXR-1000 (UHF) Service Manual page 28

Circuit Description
MHz), the temperature compensation circuit
which includes D2007 (1SS353) and thermostats
TH2001 and TH2002, and the transmit (DCS)
modulation circuit D2005/ D2006 (HVU350 × 2).
Transmitter
Voice audio from the microphone or external
inputs passes through a low-pass filter Q1005
(NJM2902M), and a limiter amplifier and low-
pass filter at Q1006 (NJM2902M), then is adjust-
ed for optimum deviation level and delivered
to the next stage.
Voice input from the microphone, or external in-
puts and CTCSS, are frequency-modulated at the
VCO of the synthesizer, while DCS audio is mod-
ulated by the reference frequency oscillator of the
synthesizer. Synthesizer output, after passing
through diode switch D2010 (1SS184), is ampli-
fied by driver Q2015 (µPC2710) and power mod-
ule Q2003 (M67799H) to obtain full RF output.
The RF energy then passes through antenna
switch D2001/ D2002 and a low-pass filter circuit
and finally to the antenna connector.
RF output power from the final amplifier is sam-
pled by C2117 and C2118 and is rectified by
D2017 (1SS321). The resulting DC is fed through
Automatic Power Controller Q2018 (TA75S01F)
to transmitter power module Q2003.
Generation of spurious products by the trans-
mitter is minimized by the fundamental carrier
frequency being equal to the final transmitting
frequency, modulated directly in the transmit
VCO. Additional harmonic suppression is pro-
vided by a low-pass filter consisting of L2001,
L2002, and L2024 and C2002, C2004, C2009,
C2111, C2112, C2113, and C2114, resulting in
more than 60 dB of harmonic suppression prior
to delivery to the RF energy to the antenna.
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DCS Demodulator
DCS signals are demodulated on the RF-UNIT,
and are applied to low-pass filter in sections 3
and 4 of Q1040 (NJM2902M), as well as the lim-
iter comparator in section 1 of Q1040.
CTCSS encoder/decoder
Generation, demodulation, and detection of the
CTCSS tones are carried out by IC Q1014
(MX165C).
MPU
Operation is controlled by 8-bit MPU IC Q1039
(HD64F3334YTF). The system clock uses a
9.8304 MHz crystal for a time base. IC Q1015
(RH5VL45AA) resets the MPU when the power
is on, and monitors the voltage of the regulated
5V power supply line.
EEPROM
The EEPROM retains Tx and Rx data for all 16
channels, CTCSS data, DCS data, prescaler di-
viding, IF frequency, local oscillator injection
side (upper/lower), and REF oscillator data (in-
ternal/external).