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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
To MCU
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.
2ndIF BPF
CF300
450KHz+/4.5K
OUT
IN
IFAmp1
U200
AN29160AA
RSSI
IFAMP2
PROCESSER
mix2
DET
VREF
SQ
tone-LPF
PE
5th-LPF
信令输出
De
Emphasis
To MCU
CDC/CTC
VCC
EN
VCO
TX
RX
MCU
LATCH
POWERREG
IC
volume
AF
mute
LIM
5th-HPF
Mic amp
(TX)
AF
HPF
SF
mic mute
AMP(TX)
Figure 7
11
POWER446 Service Manual
SPVCC
DATA
sp Amp
AUDIO OUT
16Ω IW
U201
AF
SW
AMP
0
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