TK-2107G
9
CIRCUIT DESCRIPTION /
电路说明
1. Frequency Confi guration
The receiver utilizes double conversion. The first IF is
38.85MHz and the second IF is 450kHz. The fi rst local oscil-
lator signal is supplied from the PLL circuit.
The PLL circuit in the transmitter generates the neces-
sary frequencies. Fig. 1 shows the frequencies.
2. Receiver
The frequency confi guration of the receiver is shown in
Fig. 2.
2-1. Front-end RF amplifi er
An incoming signal from the antenna is applied to an RF
amplifier (Q203) after passing through a transmit/receive
switch circuit (D102 and D103 are off) and a band pass fi lter
(L208, L209 and L210). After the signal is amplifi ed (Q203),
the signal is filtered through a band pass filter (L203 and
L214) to eliminate unwanted signals before it is passed to
the fi rst mixer. Band pass fi lters (L208, L209, L210, L203
and L214) have varactor diodes (D203, D204, D205, D202
and D201).
The voltage of these diodes are controlled by to track the
MCU (IC403) center frequency of the band pass fi lter. (See
Fig. 2)
1. 频率构成
接收部采用二次变频超外差方式。第一中频为 38.85M H z，
第二中频为 450K H z。第一本振频率信号由锁相环电路 ( P L L )
提供。
发射部由锁相环电路直接产生所需要的频率。图 1 显示各
种频率。
2. 接收部
接收部的频率构成如图 2 所示。
2-1. 前端射频放大器
从 天 线 输 入 的 信 号 经 过 收 发 转 换 电 路 ( D102 和 D103 断
开 ) 和带通滤波器 ( L208, L209 和 L210) 后，在射频放大器
( Q203) 处放大。信号被放大后 ( Q203)，在通过第一混频器之
前，经过带通滤波器 ( L203 和 L214) 滤波来消除不要的信号。
带通滤波器 ( L208, L209, L210, L203 和 L214) 有变容二极管
(D203,D204,D205,D202 和 D201)。
这些变容二极管的电压由带通滤波器的 MCU(IC403) 中心频
率控制。( 参见图 2)
Fig. 1 Frequency confi guration /
图 1 电路构成
Fig. 2 Receiver section confi guration /
图 2 接收部构成
ANT
150~174MHz
TX 150~174MHz
RX
188.85~212.85MHz
ANT
SW
RF
AMP
MCF
CF
IF
SYSTEM
AF
AMP
PA
AMP
TX
AMP
PLL
VCO
MIC
AMP
TCXO
X3
multiply
38.85MHz
450kHz
38.4MHz
12.8MHz
SP
MIC
ANT
D102,
D103
BPF
L208~L210
APC
TUNE
RF AMP
Q203
BPF
L214,L203
MIXER
Q202
MCF
XF200
IF AMP
Q201
CF200
Q1
IC300
IF, MIX, DET
IC200
AF AMP
LPF, HPF
AF PA AMP
IC302
SP
Wide/Narrow SW
Q303
X3
multiply
IC403
MCU
TCXO
1st Local OSC
(PLL)
ANT
SW
