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Circuit Description
Transmitter
Voice audio from the microphone is delivered via
the MIC (Jack) Unit to the MAIN Unit, after passing
through amplifier Q3039/Q2040 (NJM2902V), pre-
emphasis, limiter (IDC instantaneous deviation con-
trol), and LPF Q2001 (NJM2902V), is adjusted for
optimum deviation level and delivered to the next
stage.
Voice input from the microphone and CTCSS are
FM-modulated to 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 driver Q1031
(2SC3356) / Q1025 (2SC3357) and power module
Q1017 (RA60H1317M) to obtain full RF output. The
RF energy then passes through antenna switch
D2015 / D2016 and a low-pass filter circuit and fi-
nally to the antenna connector.
RF output power from the final amplifier is sam-
pled by CM coupler and is rectified by D1037, D1038
(HSM198S x 2). The resulting DC is fed through Au-
tomatic Power Controller Q1007 (NJM2904V) to
transmitter RF amplifier and thus the power out-
put.
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 L1008 L1004, L1002, L1001 and
C1338, C1336, C1337, C1335, C1334, C1333, C1332
and C1326, resulting in more than 60 dB of harmon-
ic suppression prior to delivery to 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
Q2003.
CTCSS encoder/decoder
The CTCSS code is generation and encoding 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 (RN5V35AA) 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 mem-
ory channels and CTCSS data, DCS data, prescaler
dividing, and REF oscillator data (internal/external).
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