Circuit Description - Kenwood TK-3312 Service Manual

TK-3312/3317
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: 400~470MHz
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,
L491, L414 and L413) and goes to the mixer. These BPFs
are adjusted by variable capacitance diodes (D408, D407,
D405, D404 and D403). The input voltage to the variable ca-
pacitance diodes is a regulated voltage output from the DC
amplifi er (IC811).
12

CIRCUIT DESCRIPTION

1st MIX
RF
SW AMP
49.95MHz
350.05~
420.05MHz
TX
400~470MHz
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