Circuit Description - Kenwood TK-3402(U) Service Manual

1. Frequency Confi guration
The receiver utilizes double conversion. The first IF is
50.85MHz and the second IF is 450kHz. The fi rst Local os-
cillator is supplied from the PLL circuit.
The PLL circuit in the transmitter generates the neces-
sary frequencies. Figure 1 shows the frequencies
TX/RX: 450~520MHz
ANT
ANT
SW
TX
AMP
2. Receiver System
The receiver system is shown in Figure 2.
ANT
BPF
ANT
SW
BPF1
2-1. Front End (RF Amplifi er) 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 ampli-
fi ed by the RF amplifi er (Q405).
The resulting signal passes through a BPF (L410,L411
and L413) and goes to the mixer. These BPF are adjusted by
variable capacitance diodes (D400, D401, D402, D403 and
D404). The input voltage to the variable capacitance diode is
a regulated voltage output from the DC amplifi er (IC704).

CIRCUIT DESCRIPTION

1st MIX MCF
RF
AMP
50.85MHz
399.15~
469.15MHz
RF
AMP
450~520MHz
Fig. 1 Frequency confi guration
Q405 Q404
RF AMP BPF 1st MIX
BPF1 1st Local
Fig. 2 Receiver system
TK-3402(U)/3402/3407
CF
450kHz
IF
Baseband
System
50.4MHz
X3
TCXO
Tripler
PLL
VCO
CF401
Q403
XF400 IF AMP
IC400
IF,MIX,DET
MCF
Q400
X3 Tripler
2nd Local
2-2. First Mixer
The signal from the front end is mixed with the fi rst local
oscillator signal generated in the PLL circuit by Q404 to pro-
duce a fi rst IF frequency of 50.85MHz.
The resulting signal passes through the XF400 MCF to
cut the adjacent spurious and provide the optimum charac-
teristics, such as adjacent frequency selectivity.
SP
AF
AMP
16.8MHz
MIC
MIC
AMP
IC709
AF PA
IC705 (INT)
Baseband
X1
TCXO
16.8Hz
SP
9