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POWER446 Service Manual
11
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 signaling waveform modulated on the carrier.
2) RX Audio & Signaling Process
RX
sp Amp
2ndIF BPF
SF
AMP(TX)
VOX
Tone
tone-LPF
DET
BGR
EN
RSSI
Mic amp
VCO
DATA
0
5th-LPF
IFAMP2
AF
HPF
PE
信令输出
5th-HPF
IFAmp1
SW
To MCU
IC
CF300
/4.5K
OUT
IN
VREF
TX
De
Emphasis
LATCH
AF
mute
SPVCC
volume
To MCU
CDC/CTC
MCU
mix2
mic mute
POWERREG
VCC
LIM
(TX)
SQ
AUDIO OUT
16
Ω
IW
U201
AF
AMP
U200
AN29160AA
PROCESSER
Figure 7
After demodulating the received signal, U200 outputs initial audio signal, which contains noise, signaling
and voice components. Therefore, audio is processed as follows:
a. RX audio processing: One flow of audio signal from U200 goes back to U200 after passing through
the RC low-pass filter and de-emphasis circuit. This flow of audio signal is amplified at U200, and
restored after frequencies below 300Hz are removed. The restored audio signal is adjusted by the
potentiometer and then applied to the audio power amplifier (U201), which performs power
amplification to drive the speaker directly. To obtain higher power, BTL output is adopted.
b. RX signaling processing: One flow of audio signal from U200 goes to the 300Hz low-pass filter
circuit (U640). After audio signals above 300Hz are removed, signaling (CTCSS or CDCSS) goes to
the QTIN pin of CPU. Then the input signaling is decoded by CPU.
c. Noise Signal Processing: One flow of audio signal from U200 goes back to U200. After they are
filtered, amplified and rectified at U200, a DC voltage signal (SQ) is derived and is sent to the BUSY
pin of MCU by the ND pin of U200. Then MCU processes the input signal.
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