TC-600 Service Manual
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Figure 5 Transmit CTCSS
3) DTMF/2-Tone Encoder
DTMF/2-Tone signalings are generated by IC11 and outputted in parallel by Pin 48-51. The output
signal is reshaped by resistor array CP7-CP10, then sent to IC3 (1/4) for amplification, and filtered by
active LPF consisting of Q25, Q24 and other components to eliminate the corresponding HF emission
before being passed to TX VCO for modulation. The modulated signal is applied to AF AMP through
C254 for ease of monitoring.
4) RF Amplifier
The transmit signal obtained from VCO buffer amplifier Q14 is amplified by Q15 and Q17. The
amplified signal is passed to power amplifier Q32 and Q31, and is capable of generating a 4.0W RF
power. Q50 and R617 are used to toggle between high and low power.
5) Antenna Switch and LPF
The output signal from RF amplifier is passed through a low-pass filter network and a transmit/receive
switch circuit before reaching the antenna terminal. The transmit/receive switch circuit is comprised of
D11 and D12. D11 and D12 is turned on (conductive) in transmit mode and off (isolated) in receive
mode.
5. Power
The 5V reference power supply for the control circuit is derived from a LDO IC. The reference power
provides a 5V voltage in transmit mode [T_V], a 5V voltage in receive mode [R_V], and a 5V voltage
shared in both modes based on the control signal from the microprocessor.
6. Control System
The IC11 CPU operates at 7.3728MHz.