TC- 446 Service Manual
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4.
Transmitter
1)
Transmit audio
The audio signal from microphone is amplified through IC3, and then pre-emphasized , and
then filtered by another low-pass filter
(
separate filter
)
(Q25 and Q24) to eliminate the
frequencies over 3KHz. The resulting signal enters the VCO for direct FM modulation. (See
figure 5)
2)
CTCSS/CDCSS Encoder
The necessary frequency for CTCSS/CDCSS encoder is generated by IC11 and
FM-modulated to the PLL reference signal. Since the reference OSC does not modulate the
loop characteristic frequency or higher, modulation is performed at the VCO side by splitter.
(See figure 5)
Figure 5 transmit CTCSS
3)
RF amplifier
The transmit signal obtained from VCO buffer amplifier Q14 is amplified by Q15 and Q17.
This amplified signal is passed to power amplifier Q32 and Q31, and is capable of producing
a 4.0W RF power.
4)
Antenna Switch and LPF
The RF amplifier output signal is passed through a low-pass filter network and a
transmit/receive switch circuit before it is passed to the antenna terminal. The
transmit/receive switch circuit is comprised of D11 and D12. D11 and D12 is turned on in
transmit mode and off in receive mode.
5.
Power
The 5V reference power supply for the control circuit is derived from an internal battery. The
reference power provides a 5V supply in transmit mode [T_V], a 5V supply in receive mode [R_V],
and a 5V supply shared in both modes based the control signal from the microprocessor.
6.
Control System
The IC11 CPU operates at 7.3728MHz.
Summary of Contents for TC-446
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