HYT TC-508, Service Manual

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TC-508 Service Manual
10
After the RF signals are received from the antenna, the undesired out-of-band signals are filtered out at
the bandpass filter. Then the remaining RF signals are amplified by LNA Q501. Afterwards, the amplified
signal goes through the bandpass filter again to eliminate undesired out-of-band interference signal.
After being filtered and amplified, the RF signals and first LO signals are mixed at Q502, and then the
mixed signal is filtered by crystal filter XF501 to get 38.85MHz differential signals as the first IF signal.
After being amplified by Q506, the IF signal goes to chip U611, where the signal will be mixed with the
second LO signal (38.4MHZ). Next, the signals will be filtered by CF501 to produce 450KHz IF signal.
When the IF signals are processed by demodulation circuit (including U611 and CD501) to generate
audio signals, which are delivered to IC Q613 for amplification and output in two channels. After simple
filtering, one channel of signals is sent to MCU U601 for CTCSS/CDCSS decoding; for the other channel,
it goes through two stages of low-pass filter first, and then it goes to high-pass filter U610 (consisting of
four operational amplifiers) for audio processing. Finally, the signals will be sent to audio power amplifier
U302 for amplification so as to drive the speaker.
2.4 MCU Control, Signal Processing and Audio Power Amplification
U601
MCU
SRT3210
MICJACK
VOX_DET
Q611
D616
R204
C204
C205
R607
R632
R206
AF AMP
U302
SW
VOLUME
S201
S
W
_
C
H
A
N
N
A
L
RESET IC
U605
E 2ROM
U603
DATA/ STB/ CK
LD
T
X
_
C
T
L
S
A
V
E
SDA/ SCL
RESE T
EC0/EC1/EC2/ EC3
MODE
A
F
V
O
X
1
2
PTT/SK1/SK2
APC
M
IC
IN
R
_
L
E
D
T
_
L
E
D
LED
D601
LED
D602
SPK
MODE_OUT
RXD
TXD
SP_JACK
J3
PJ-D3027 D
1
2
MIC
B201
QT_OUT
T/ R
QT _OUT
QT _MODULATING
FILLER
AF_MODULATING
FILLER
BATTERY
G602
W/N
AF_SW
Q 302
B
E
E
P
B
E
E
P
A
F
_
M
U
T
E
R
F
_M
U
T
E
Figure 5