Circuit Description - Kenwood TK-2402(V) Service Manual

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 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: 136~174MHz
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 (L411) and
goes to the mixer. These BPF are adjusted by variable ca-
pacitance diodes (D401, D402, D403 and D404). The input
voltage to the variable capacitance diode is a regulated volt-
age output from the DC amplifi er (IC704).
TK-2402(V)/2402/2406/2407

CIRCUIT DESCRIPTION

1st MIX MCF
RF
AMP
38.85MHz
174.85~
212.85MHz
RF
AMP
136~174MHz
Fig. 1 Frequency confi guration
Q405 Q404
RF AMP BPF 1st MIX
BPF1 1st Local
Fig. 2 Receiver system
CF
450kHz
IF
Baseband
System
38.4MHz
X2
TCXO
doubler
PLL
VCO
CF401
Q403
XF400 IF AMP
IC401
IF,MIX,DET
MCF
Q400
X2 doubler
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 Q406 to pro-
duce a fi rst IF frequency of 38.85MHz.
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
19.2MHz
MIC
MIC
AMP
IC709
AF PA
IC705 (INT)
Baseband
X1
TCXO
19.2Hz
SP
9