Audio And Signalling Process Circuit; Diagram For Tx Audio & Signalling Process - HYT TC-610 Service Manual

According to the selected channel, MCU outputs the corresponding PWM waveform, which is reshaped
by the RC filter network (R441, R442, C440 and C441) to derive the level for the APC/TUNE control
signal. One part is used as the control voltage of the Rx electrically tunable circuit after passing through
R500. In transmit mode, the level is voltage-divided by R439 and R440 to obtain the APC reference
voltage.
The transmit current passes through R420, R421 and R422 to derive the error detect voltage. The
voltage is amplified by operational amplifier U430 and then compared with the APC reference voltage to
output the APC control voltage and to form control power of closed-loop negative feedback when the
transmit current changes.

Audio and Signalling Process Circuit

Baseband processor AN29160 has high integration level and powerful functions. Many of the process
functions (as VCO level detect & output, SQ signal level detect & output, Tx-Rx audio process switch,
audio amplifier, etc) can be realized inside and can be used in both receive and transmit modes.
1. Diagram for Tx Audio & Signalling Process
cpu
Tx Audio Process: The audio signal input from the MIC is converted to electrical signal through the
audioelectric conversion of MIC and the amplitude limit is amplified at U200 after the signal is
pre-emphasized. The processed signal goes to the low-pass filter circuit to remove frequencies above
3KHz and then goes to VCO for direct frequency modulation after passing through potentiometer VR200.
Tx Sinalling Process: MCU outputs, via the QTO port, signalling encoder waveform, which is divided into
two parts for modulation after passing through the RC network. One part is used to modulate PLL
reference frequency oscillator directly, while the other part is used to modulate VCO. VR260 balances
the modulation and adjusts the signal amplitude ratio of one part to the other, which optimizes the
singalling waveform modulated on the carrier.
AF
mute
LIM
5th-HPF
Mic amp
(TX)
AF
HPF
mic mute
Pre
Emphasis
U200
volume
AN29160AA
sp Amp
PROCESSER
SF
AMP(TX)
AFMOD
MIC
mic
0
Figure 7
15
TC-610/620 Service Manual
D104
信令输入
TX-VCO
Q100
2SK508NV