Kenwood TK-3401D Service Manual page 6

2.3 CIRCUIT DESCRIPTION
2.3.1 Frequency Configuration
The receiver utilizes double conversion. The first IF is 49.95MHz and the second IF is 450kHz. The first Local oscillator is supplied
from the PLL circuit.
The PLL circuit in the transmitter generates the necessary frequencies. Figure 1 shows the frequencies.
TX/RX: 446.00625~446.196875MHz
ANT
ANT
SW
TX
AMP
2.3.2 Receiver System
The receiver system is shown in Figure 2.
ANT
BPF
ANT
SW
BPF1
2.3.2.1 Front End (RF Amplifier) Circuit
The signal coming from the antenna passes through the transmit/receive switching diode circuit (D201, D202, D203 and D204) and a
BPF (L415 and L416), and is then amplified by the RF amplifier (Q405).
The resulting signal passes through a BPF (L410,L411 and L413) and goes to the mixer. The BPF is adjusted by variable capacitance
diodes (D400, D401, D402, D403 and D404). The input voltage to the variable capacitance diodes is the regulated voltage output from
the DC amplifier (IC704).
2.3.2.2 First Mixer
The signal from the front end is mixed with the first local oscillator signal generated in the PLL circuit by Q404 to produce the first IF
frequency of 49.95MHz.
The resulting signal passes through the XF400 MCF to cut the adjacent spurious and provide optimum characteristics, such as adja-
cent frequency selectivity.
1-6 (No.RA012<Rev.001>)
1st MIX MCF
RF
AMP
49.95MHz
RX:396.05625~
396.246875MHz
RF
AMP
TX:446.00625~
446.196875MHz
Fig.1 Frequency configuration
Q405 Q404
RF AMP BPF 1st MIX
BPF1 1st Local
Fig.2 Receiver system
IF
Baseband
System
50.4MHz
x3
TCXO
Tripler
PLL
VCO
Q403
XF400 IF AMP
IC400
IF,MIX,DET
MCF
Q400
x3 Tripler
2nd Local
SP
AF
AMP
16.8MHz
MIC
MIC
AMP
IC709
AF PA
IC705 (INT)
Baseband
X1
TCXO
16.8MHz
SP