Vertex Standard VX-6000L Service Manual page 14

Transmitter
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), to obtain the required RF
drive prior to delivery to the PA Unit. There the RF
signal is amplified by parallel junction transistors
Q6006/Q6007 (SD1405X2) and passes through an-
tenna switching relay RL6001 and a low-pass filter
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 D6006/D6007
(MA729X2). The resulting DC is fed through Auto-
matic Power Controller Q1038 (NJM2902V), Q1001
(2SC4154E), Q1004 (2SB1132Q) 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. Additional
harmonic suppression is provided by a low-pass fil-
ter consisting of L6009/L6010/L6011 and C6042/
C6043/C6044/C6047/C6074/C6075 and C6045, result-
ing in more than 65 dB of harmonic suppression pri-
or to delivery of the RF energy to the antenna.
VX-6000 VHF Low-Band Service Manual
Circuit Description
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 Q2110
(NJM2902V).
CTCSS Encoder/Decoder
The CTCSS code is generated and encoded by
MPU IC Q2019 (MB90F583B). Demodulation and
detection of the CTCSS tones are carried out by IC
Q2013 (MX165C).
MPU
Operation is controlled by 16-bit MPU IC Q2026
(MB90F583B). The system clock uses a 16.000 MHz
crystal for a time base. IC Q2036 (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).
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