Vertex Standard VX-6000V 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/Q2041 (NJM2902V), pre-
emphasis, limiter (IDC instantaneous deviation con-
trol), and low-pass filter Q2001 (NJM2902V); the sig-
nal is adjusted for optimum deviation level and de-
livered to the next stage.
Voice inputs from the microphone and CTCSS are
FM-modulated at the VCO of the synthesizer, while
DCS audio is modulated by the reference frequency
oscillator of the synthesizer.
Synthesizer output, after passing through diode
switch D1025 (1SS321), is amplified by drivers
Q1031 (2SC5415E) and Q1025 (2SC2954) and pow-
er module Q1017 (M67781H) to obtain the required
RF drive prior to delivery to the PA Unit. There the
RF signal is amplified by parallel junction transis-
tors Q6001/Q6002 (2SC5125X2) and passes through
antenna switching relay RL6001 and a low-pass fil-
ter circuit, and ultimately to the antenna connector.
RF output power from the final amplifier is sam-
pled by a CM coupler and is rectified by D6002 and
D6003 (HSM88ASX2). The resulting DC is fed
through Automatic Power Controller Q1007
( N J M 2 9 0 2 V ) , 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 L6007, L6008, L6009, and C6027,
C6039, C6050, C6040, C6047 and C6041, resulting in
more than 65 dB of harmonic suppression prior to
delivery of the RF energy to the antenna.
4-2
DCS Demodulator
DCS signals are demodulated on the MAIN-
UNIT, and are applied to low-pass filter Q2040
(NJM2902V), as well as the limiter comparator
Q2040 (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 (MX165C).
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 Q2035 (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).