Service Manual

13
Audio and Signalling Processing Circuit
Baseband processing IC AN29160 has high integration level and powerful functions. Many of the
processing functions (as VCO level detect&output, SQ signal level detect&output, Tx-Rx audio
processing switch, audio amplifier, etc) and can be realized inside. The Tx-Rx sharing can also be
realized.
Block Diagram for Tx Audio&Signalling Process
D104
Q100
2SK508NV
TX-VCO
cpu
Pre
Emphasis
SF
AMP(TX)
sp Amp
Tone
AFMOD
Mic amp
U200
AN29160AA
PROCESSER
信令输入
AF
HPF
5th-HPF
mic
MIC
AF
mute
volume
mic mute
LIM
(TX)
0
Figure 7
Tx Audio Process: Audio signals input from the MIC is converted to electrical signals through the
audioelectric conversion of MIC and the amplitude limit of them are amplified by U200 after the
signals are pre-emphasized. The processed signals go to the low-pass filter circuit to remove
frequencies above 3KHz and then go 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 adjust the signal amplitude ratio of one part to the other, which
optimizes the singalling waveform modulated on the carrier.