HYT POWER446, Service Manual, Page: 12 / 61

POWER446 Service Manual
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MCU outputs appropriate PWM waveform according to the selected channel. This waveform is then
rectified by the RC filter circuit (R441, R442, C440 and C441) to generate level of APC/TUNE control
signal. One flow of the signal goes to R500 to serve as control voltage of the RX electrically tunable
circuit. In TX mode, the signal goes to R439 and R440 for voltage division, so as to get APC reference
voltage.
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 amplifier 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) TX Audio & Signaling 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 6
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.