Vertex Standard VX-6000U Service Manual page 21

Circuit Description
Transmitter
During transmit, the PLL synthesizer oscillates
at the desired frequency directly, for amplification
to obtain RF power output. During transmission,
voice modulation and CTCSS (or DCS) modulation
are applied to this synthesizer.
Voice audio from the microphone is delivered via
the Mic (Jack) Unit to the MAIN Unit, after passing
through amplifier Q3039/Q2108 (NJM2902V), pre-
emphasis, limiter (IDC instantaneous deviation con-
trol), and LPF Q2001 (NJM2902V); the signal is ad-
justed for optimum deviation level and delivered to
the next stage.
Voice inputs from the microphone and CTCSS are
frequency-modulated to the VCO of the synthesiz-
er, while DCS audio is modulated by the reference
frequency oscillator of the synthesizer.
Synthesizer output, after passing through diode
switch D1022 (1SS321), is amplified by drivers
Q1024 (2SC2954)/Q1030 (2SC5415E)/Q1035
(2SC5107) and power module Q1014 (M68769H) to
obtain the required RF drive prior to delivery to the
PA Unit. There the RF signal is amplified by paral-
lel junction transistors Q6001/Q6002 (2SC3102) and
passes through antenna switching relay RL6001 and
a low-pass filter circuit, and ultimately to the anten-
na connector.
RF output power from the final amplifier is sam-
pled by a directional coupler and is rectified by
D6002/D6003 (HSM88ASX2). The resulting DC is
fed through Automatic Power Controller Q1007
( M 5 2 2 3 A G P ) , Q 1 0 0 1 ( 2 S C 4 1 5 4 E ) , Q 1 0 0 2
(2SB1143S) to control the gain of the transmitter
RF amplifier and thus regulate the power output.
Generation of spurious products by the transmit-
ter is minimized by the fundamental carrier frequen-
cy being equal to the final transmitting frequency,
modulated directly in the transmit VCO. Addition-
al harmonic suppression is provided by a low-pass
filter consisting of L6003/L6004/L6005 and C6023/
C6024/C6025, resulting in more than 80 dB of har-
monic suppression prior to delivery of the RF ener-
gy to the antenna.
4-2
DCS Demodulator
DCS signals are demodulated on the MAIN-
UNIT, and are applied to low-pass filter Q2110
(NJM2902V), as well as the limiter comparator
Q2003 (NJM2902V).
CTCSS Encoder/Decoder
The CTCSS code is generated and encoded by
MPU IC Q2025 (MB90F583B). Demodulation and
detection of the CTCSS tones are carried out by IC
Q2017 (MX165CDW).
MPU
Operation is controlled by 16-bit MPU IC Q2025
(MB90F583B). The system clock uses a 16.000 MHz
crystal for a time base. IC Q2034 (RN5VL35AA) re-
sets 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 mem-
ory channels, as well as CTCSS data, DCS data, pres-
caler dividing, and REF oscillator data (internal/ex-
ternal).