Vox Realization Circuit - HYT POWER446 Service Manual

8. VOX Realization Circuit

VCC_5V
C274
R251
1M 0.01U
L200
Press the programmed VOX key, and the radio enters the VOX status. The VOX can be activated only
when MIC_EN and EXT-PTT are detected by MCU to switch from low level to high level within several
hundred milliseconds. Otherwise, it is detected as the earpiece without VOX so as to disable the VOX
function.
1. When a VOX earpiece is plugged into the accessory jack, Q201 is cut off, and MIC_EN switches
from low level to high level. Meantime, Q202 and R204 form a loop circuit with the external earpiece
(Q202 is conductive), and EXT-PTT switches from low level to high level. In this case, the VOX
earpiece is determined by MCU, and the VOX function is enabled. When the VOX level (5 selectable
levels) gets to the preset value, transmission is initiated, and the voice signal enters the baseband
processor (AN29160) via the processing path.
2. If it is an earpiece without VOX (namely an earpiece with PTT), Q201 is cut off, and MIC_EN
switches from low level to high level. However, Q202 does not form a loop circuit (maintaining the
cut-off status) and EXT-PTT is still at low level. In this case, MCU detects it as the earpiece without
VOX. The radio will return to normal mode, and will transmit if the PTT key on the earpiece is held
down.
R206 1K
C212
R205
0.1U
47K
C213
1U
Q201
2SK1824
2
R203
4.7K
1UH
Q202
2SA1832
2 3
R207
56K
R204 470
C260
R202 100
220P
TP200
C202
0.1U
C201 R201
470P 2.2K
C200 R200
4.7u/10V 470
Figure 10
14
POWER446 Service Manual
R208
100K
J4
MICJACK
X1
2
-
1 mic
+
VCC_5V
EXPTT
MIC_EN
RXD