HYT TC-618, Service Manual

Page: 19 / 110

TC-618/626 Service Manual
18
8. VOX Realization Circuit
The block diagram is shown in the figure below:
Q202
2SA1832
1
2 3
Q201
2SK1824
2
3
1
J4
MICJACK
2
4
3
1
VCC_5V
R251
1M
MIC_EN
EXPTT
C260
220P
RXD
mic
X1
-
2
+
1
R201
2.2K
C201
470P
C200
4.7u/10V
R203
4.7K
VCC_5V
R200
470
C213
1U
C212
0.1U
R205
47K
C202
0.1U
L200 1UH
R202 100
TP200
R208
100K
R207
56K
R206 1K
R204 470
C274
0.01U
Figure 10
Press and hold down the programmed VOX key, and the radio enters the VOX status. The VOX function
can be enabled only when MIC_EN and EXT-PTT are detected by MCU to switch from low level to high
level within several hundred milliseconds. Otherwise, the earpiece will be deemed as one without VOX
and the VOX function cannot be enabled.
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 closed 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
levels, adjustable) reaches the preset value, voice operated transmission is being made, and the
voice signals enter the baseband processor (AN29160) via the processing path.
2) If a non-VOX earpiece (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 closed circuit (maintaining the cut-off status)
and EXT-PTT is still at low level. In this case, a non-VOX earpiece is determined by MCU. The
radio will return to normal mode, and will transmit if the PTT key on the earpiece is held down.