11
TK-2118
TK-260
:K, K2
1. Frequency configuration
The receiver utilizes double conversion. The first IF is
51.65MHz and the second IF is 450kHz. The first local
oscillator signal is supplied from the PLL circuit.
The PLL circuit in the transmitter generates the necessary
frequencies. Fig. 1 shows the frequencies.
CIRCUIT DESCRIPTION /
电路说明
ANT
ANT SW
RF
AMP
MCF
CF
IF SYSTEM
AF
AMP
RX
TX
PA
AMP
TX
AMP
PLL
VCO
MIC
AMP
TCXO
X4
multiply
51.65MHz
450kHz
51.2MHz
12.8MHz
SP
MIC
Fig. 1 Frequency configuration /
图1 电路构成
ANT
D24, D25
D26, D27
BPF
APC
TUNE
RF AMP
Q20
BPF
MIXER
Q12
MCF
XF1
IF AMP
Q6
CF1
IF, MIX, DET
IC2
AF AMP
LPF, HPF
IC306
AF PA AMP
IC309
SP
WIDE/NARROW SW
Q316
X4
multiply
Q2
IC300
MPU
TCXO
1st Local OSC
(PLL)
ANT SW
2. Receiver
The receiver is double conversion superheterodyne,
designed to operate in the frequency range of 150 to 174MHz
(C type), 136 to 150MHz (C2 type).
The frequency configuration is shown in Fig. 1.
1) Front - end RF amplifier
An incoming signal from the antenna is applied to an RF
amplifier (Q20) after passing through a transmit/receive switch
circuit (D24, D25, D26, AND D27 are off) and a band pass
filter (L44, L47 and L49). After the signal is amplified (Q20),
the signal is filtered through a band pass filter (L34 and L40) to
eliminate unwanted signals before it is passed to the first
mixer. Band pass filters (L44, L47, L49, L34 and L40) have
varactor diodes (D21, D22, D23, D16 and D20).
The voltage of these diodes are controlled by to track the
MPU (IC300) center frequency of the band pass filter. (See
Fig. 2)
Fig. 2 Receiver section configuration /
图2 接收部构成
1. 频率构成
接收部采用二次变频超外差方式。第一中频为51.65MHz·第
二中频为4 5 0 K 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
接收部为二次变频超外差方式,设计操作的频率范围是1 5 0 -
174MHz (C),136-150MHz (C2)。
1) 前端射频放大器
从天线输入的信号经过收发转换电路 (D24, D25, D26和D27断
开) 和带通滤波器 (L44, L47和L49) 后,在射频放大器 (Q20) 处放
大。信号被放大后 ( Q 2 0 ),在通过第一混频器之前,经过带通
滤波器 (L34和L40) 滤波来消除不要的信号。带通滤波器(L44,
L47, L49, L34和L40) 有变容二极管 (D21, D22, D23, D16和D20)。
这些变容二极管的电压由带通滤波器的MPU (IC300) 中心频
率控制。(参见图2)