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TP620 Service Manual
3. Circuit Description
3.1. Tx/Rx Signal Procedure
Figure 3-1 RF Schematic Diagram
ANT
LPF
RF AMP
Q505
MCF
IF AMP
Q507
GT3136
450K
AF AMP
AF PA
SPK
D501 D503
D504
XF501
49.95MHz
U102 NJM2902
IC101 TDA8547
TX/RX
SW
BPF
BPF
MIXER
CF501 450H
16.8MHz
TCXO
16.8MHz
To 50.4MHz
Q605
X601
Q509
450_IF AMP
CODEC
U201
HR_C5000
Q506 3SK318
PLL
2SK72310
Loop
Filter
TX VCO
RX VCO
Buffer
PA
Pre-driver
PA
driver
PA
Final
Q504 2SC3356
Q503 2SC3356
Q502 RD01
Q501 RD07
MIC
AF
AMP
CODEC
MOD_I
MOD_Q
U103
NJM2100
3.1.1. Tx Circuit
Figure 3-2 Tx Circuit Diagram
ANT
LPF
D501 D503
D504
TX/RX
SW
16.8MHz
TCXO
X601
U201
HR_C5000
PLL
2SK72310
Loop
Filter
TX VCO
Buffer
PA
Pre-driver
PA
driver
PA
Final
Q504 2SC3356
Q503 2SC3356
Q502 RD01
Q501 RD07
MIC
AF
AMP
CODEC
MOD_I
MOD_Q
U103
NJM2100
BATT+
APC
APC
U502
Tx circuit mainly includes four parts below:
•
RF Power Amplifier Circuit
The carrier signal generated by VCO will be modulated and preliminarily amplified before entering Tx
circuit. The signal will first pass
through a Π-type pure resistance attenuator R536 R537 R538 to realize
the level isolation between the power amplifier circuit and Tx VCO. Then the modulation signal enters the
first pre-drive amplifier (Q504) for preliminary amplification, which generates a certain isolation between
the first and second amplifier; The amplified signal will then enter the next pre- drive amplifier (Q503 and
drive amplifier (Q502 RD01)) for further power amplification so as to ensure that enough drive power
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