Circuit Description - Kenwood TK-3312 Service Manual

TK-3312/3317
1. Frequency Configuration
The receiver utilizes double conversion. The first IF is
49.95MHz and the second IF is 450kHz. The first Local os-
cillator is supplied from the PLL circuit.
The PLL circuit in the transmitter generates the neces-
sary 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 Amplifier) 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 ampli-
fied by the RF amplifier (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
amplifier (IC811).
12

CIRCUIT DESCRIPTION

1st MIX MCF
RF
AMP
49.95MHz
400.05~
470.05MHz
RF
AMP
450~520MHz
Fig. 1 Frequency configuration
Q407 Q406
RF AMP BPF 1st MIX
BPF1 1st Local
Fig. 2 Receiver system
CF
450kHz
IF AF
System baseband
50.4MHz
X3
TCXO
multiply
PLL
VCO
CF402 CF401
Q405
XF401 IF AMP
IC401
IF,MIX,DET
MCF
Q403
X3 multiply
2nd Local
2-2. First Mixer
The signal from the front end is mixed with the first local
oscillator signal generated in the PLL circuit by Q406 to pro-
duce a first 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
AMP
16.8MHz
MIC
MIC
AMP
IC815
IC812 AF PA
AF
baseband
X1
TCXO
16.8MHz
SP