HYT TC-610P Service Manual page 17

The error detect voltage is derived after the Tx current goes through R420, R421 and R422. Then the
voltage is compared and amplified by the operational amplfier U430, and further compared with the APC
reference voltage. After these operations, the APC control voltage is output, and the close-loop negative
feedback control power is generated when the Tx current changes.
5. Audio and Signaling Processing Circuit
The baseband processor (AN29160) is highly integrated and has multiple functions such as VOX Level
Detect & Output, SQ Level Detect & Output, Rx/Tx Audio Process & Convert, Audio Amplify, etc. In
addition, it can be used for both transmission and reception.
1） Block diagram of Tx audio and signaling processing:
CPU
a) Tx audio processing: The audio signal from MIC is converted to electrical signal via acoustoelectric
conversion of MIC. After pre-emphasized, the audio signal is processed by a limiting amplifier (at
U200). Then the processed signal goes to the low-pass filter circuit to remove frequencies over
3KHz. Finally, the signal goes to the potentiometer (VR200) and then to VCO for direct frequency
modulation.
b) Tx signaling processing: MCU outputs, via the QTO port, signaling code waveform, which is divided
via RC circuit into two flows. One flow modulates the reference frequency oscillator of PLL directly,
while the other flow modulates VCO. Note: VR260 adjusts the amplitude proportion between the two
flows, to optimize the singaling waveform modulated on the carrier.
AF
mute
5th-HPF
Mic amp
AF
HPF
mic mute
Pre
Emphasis
volume
LIM
sp Amp
(TX)
SF
AMP(TX)
AUDIO OUT
M IC3
mic
0
Figure 6
15
TC-610P Service Manual
U200
AN29160AA
PROCESSER
AFMOD
TX VCO
signalling input