HYT TC-700P, Руководство по обслуживанию

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TC-700P Service Manual
11
The APC circuit stabilizes the output TX power by detecting the drain current of the final-stage amplifier.
The voltage comparison circuit (U401 (2/2)) compares the voltage derived from the final-stage current
with the preset reference voltage. The APC voltage is proportional to the difference between the auto
detection voltage (output by U401 (1/2)) and the reference voltage. This output voltage controls FET PA
to ensure constant output TX power. You can control the APC voltage via a microprocessor to adjust the
output power of the TX circuit.
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Antenna Switch and LPF
Before going to the antenna, the signal output by the RF amplifier passes through a low-pass filter (LPF)
circuit and a TX-RX switch circuit ( composed of D403, D407 and D408). D407 and D408 are turned on
in TX mode, and turned off in RX mode.
6. Audio and Signaling Processing Circuit
Figure 5 Diagram of Audio and Signaling Processing Circuit
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CTCSS/CDCSS
TX: CTCSS/CDCSS generated by CTC_PLL is sent to VCXO via the low-pass filter. After passing the
low-pass filter, CTCSS/CDCSS generated by CTC_OUT is mixed with the audio signal and then
sent to VCO.
RX: The demodulated signal passes through U201 and U205, and then enters MCU, which determines
whether the received CTCSS/CDCSS is consistent with the preset value, and controls audio output
via AF_MUTE.
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2-Tone/5-Tone/DTMF