Circuit Description - HYT TC-508 Service Manual

Service Manual

5. Circuit Description

General Principle Diagram
5.1
The general circuit is composed of RDA chip circuit, TX circuit, RX circuit, power supply circuit, control
circuit, etc. See the block diagram below:
MIC
B201
2
1
2
1
AF AMP
U302
BAT
BATTERY
G602
LED
SPK
D602
LED
D601
MC9S08AC60
E2ROM
SDA/SCL
U603
VCC
VDD
Swich
5V
VT Q409
Q408
RDA Circuit: This chip is highly integrated. Its function includes voice signal
processing/modulation/demodulation, DSP, VCO, PLL, LNA and RF IF. The voice signal from MIC goes
to RDA chip for amplification. Next, the amplified voice signal will undergo a series of processing
including A/D conversion, filtering, pre-emphasizing, gain control, amplitude limit and D/A conversion.
Then the analog voice signal is delivered to VCO and amplified to a signal with 8dBm. When the RX RF
signal enters this chip, it would experience demodulation, filtering, de-emphasizing and gain control.
Finally, the signal is output to the audio amplifier.
TX section: The modulated RF signal from RDA chip goes to Q407 and Q402 for amplification, and
then further amplified by Q403. Then the amplified signal is delivered to low-pass filter to filter out the
high-order harmonics. Finally, it is sent via the antenna.
RX section: After going through LPF and amplitude limiter, the RF signal received from the antenna
enters Q501 LNA for amplification. Then the BPF will filter the signal to remove other unwanted
SP_JACK
J3
PJ-D3027D
MICJACK
VOX_DET
U613
D656
EXT_PTT
/EXT_MIC
RXD
U622
MCU
TXD
CSS/CODE/INT/SDO
/RXON/TXON/SQ/PDN
LDO
U621
V_BAT
LDO
U619
PA
Q407
2SC3356
VT
APC
DAC/ADC
VDD
3 4
DSP
2 1
U101
RDA1846
11
Circuit Description
PA PA
Q402 Q403
RD01 RD07
BIAS DOWN
APC
U401
BAT
VT
VT
VRCR
5V
RX_EN
LNA
Q501
AT41511
BPF1
ANT LPF
D401 D402