HYT TC-500, Руководство по обслуживанию, Страница: 13 / 77

TC-500 Service Manual
12
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.
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.
Control System
The IC11 CPU operates at 7.3728MHz.