Kenwood TK-P721, Service Manual, Page: 12 / 52

TK-P721
12
1. Frequency Confi
guration
The receiver utilizes double conversion. The first IF is
4 9 . 9
5MHz 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: 136~174MHz
185.95~
223.95MHz
136~174MHz
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 L41
9 ), and is then ampli-
fi ed by the RF amplifi er (Q407).
The resulting signal passes through a BPF (L41 9 , 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).
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 4
9 . 9 5MHz.
The resulting signal passes through the XF401 MCF to
cut the adjacent spurious and provide the optimum charac-
teristics, such as adjacent frequency selectivity.