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1. Frequency configuration
The receiver utilizes double conversion. The first IF is
38.85MHz 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.
2. Receiver
The receiver is double conversion superheterodyne,
designed to operate in the frequency range of 450 to 470MHz
(C type), 400 to 420MHz (C4 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) and a 3-pole LC filter. After
the signal is amplified (Q20), the signal is filtered by a band
pass filter (a 3-pole LC filter) to eliminate unwanted signals
before it is passed to the first mixer.
The voltage of these diodes are controlled by to track the MPU
(IC300) center frequency of the band pass filter. (See Fig. 2)
ANT
BPF
D24,D25
D26,D27
ANT SW
TUNE
APC
IC300
MPU
TK-260
:K, K2
CIRCUIT DESCRIPTION /
ANT
RF
ANT SW
AMP
38.85MHz
RX
PA
TX
AMP
AMP
TX
Fig. 1 Frequency configuration / 图1 电路构成
RF AMP
MIXER
BPF
Q20
Q12
1st Local OSC
(PLL)
Fig. 2 Receiver section configuration / 图2 接收部构成
电路说明
1. 频率构成
接收部采用二次变频超外差方式。第一中频为38.85MHz，第
二中频为450KHz。第一本振频率信号由锁相环电路(ＰＬＬ)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。
CF
450kHz
MCF
AF
IF SYSTEM
AMP
38.4MHz
X3
multiply
TCXO
12.8MHz
PLL
MIC
VCO
AMP
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4 5 0 -
470MHz (C)，400-420MHz (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)和三极管LC通滤波器后，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( 一
个三极管LC滤波器)滤波来消除不要的信号。
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)
MCF
IF AMP
XF1
Q6
IF, MIX, DET
TCXO
TK-3118
SP
MIC
CF1
AF PA AMP
IC309
AF AMP
LPF, HPF
IC2
IC306
X3
multiply
Q2
WIDE/NARROW SW
Q316
SP
11
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