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TK-3312/3317
12
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.
CIRCUIT DESCRIPTION
2. Receiver System
The receiver system is shown in Figure 2.
Fig. 1 Frequency confi guration
Fig. 2 Receiver system
TX/RX: 400~470MHz
350.05~
420.05MHz
400~470MHz
1st MIX
MCF
SP
MIC
CF
450kHz
ANT
ANT
SW
RF
AMP
IF
System
X3
multiply
PLL
VCO
49.95MHz
50.4MHz
TX
AMP
RF
AMP
AF
AMP
MIC
AMP
AF
baseband
TCXO
16.8MHz
SP
ANT
IC401
IF,MIX,DET
Q406
1st MIX
ANT
SW
Q403
X3 multiply
2nd Local
X1
TCXO
16.8MHz
AF
baseband
IC812
BPF1
BPF
Q407
RF AMP
XF401
MCF
Q405
IF AMP
IC815
AF PA
BPF1
1st Local
BPF
CF402
CF401
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).
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.