Circuit Description - Kenwood TK-2312 Service Manual

TK-2312/2317
1. Frequency Confi guration
The receiver utilizes double conversion. The first IF is
49.95MHz 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.
TX/RX: 136~174MHz
ANT
ANT
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 (L418 and L419), and is then amplifi ed
by the RF amplifi er (Q407).
The resulting signal passes through a BPF (L419, L418,
L416 and L414) and goes to the mixer. These BPFs are ad-
justed by variable capacitance diodes (D408, D407, D405
and D404). The input voltage to the variable capacitance
diodes is a regulated voltage output from the DC amplifi er
(IC811).
12

CIRCUIT DESCRIPTION

1st MIX
RF
SW AMP
49.95MHz
185.95~
223.95MHz
TX
136~174MHz
Fig. 1 Frequency confi guration
Q407 Q406
RF AMP BPF 1st MIX
BPF1 1st Local
Fig. 2 Receiver system
CF
450kHz
MCF
IF
System baseband
50.4MHz
X3
TCXO
multiply
RF PLL
AMP VCO
CF402
Q405
XF401 IF AMP
IF,MIX,DET
MCF
X3 multiply
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 49.95MHz.
The resulting signal passes through the XF401 MCF to
cut the adjacent spurious and provide the optimum charac-
teristics, such as adjacent frequency selectivity.
SP
AF AF
AMP
16.8MHz
MIC
MIC
AMP
CF401
IC812
IC401 AF
baseband
Q403 X1
TCXO
2nd Local 16.8MHz
IC815
AF PA SP