Kenwood TH-D72A Service Manual page 6

TH-D72A/D72E
3-2. UHF receiver circuit
■ A band UHF receiver circuit
The reception signal from the antenna passes through a
fi lter circuit and goes to the RF amplifi er (Q10). The ampli-
fi ed signal then enters the band-pass fi lter. After the signal
passes through the band-pass fi lter, it is amplifi ed by a sec-
ond RF amplifi er (Q6) and passed through the band-pass fi l-
ter before entering the mixer (Q3). The signal converted by
the fi rst-local oscillator (Lower heterodyne) to generate the
fi rst IF signal (49.950MHz) passes through the MCF (XF351),
is amplifi ed by the IF amplifi er (Q358) and then enters the
FM IC (IC353). The signal is converted to the second IF
signal (455kHz) by the second-local oscillator (Upper hetero-
dyne) which generated three times to 50.400MHz and is
detected to generate an audio signal.
A band
AF
IC352
B band
D352
SW
AF
SW
IC351
D351
AM
AGC
DET
6
CIRCUIT DESCRIPTION
CF352
2nd Local
50.400MHz
450kHz
IC353
A band demodulator
DET
2nd Local
IC354 45.505MHz
B band demodulator
DET
Q352 Q354 Q356
CF351
455kHz
Q353
SW
Q355
Figure 2-2 UHF receiver circuit
■ B band UHF receiver circuit
The reception signal from the antenna passes through a
fi lter circuit and goes to the RF amplifi er (Q9). The amplifi ed
signal then enters the band-pass fi lter. After the signal pass-
es through the band-pass fi lter, it is amplifi ed by a second
RF amplifi er (Q5) and passed through the band-pass fi lter
before entering the mixer (Q1). The signal converted by the
fi rst-local oscillator (Lower heterodyne) to generate the fi rst
IF signal (45.050MHz) passes through the MCF (XF352), is
amplifi ed by the IF amplifi er (Q359) and then enters the FM
IC (IC354). The signal is converted to the second IF signal
(455kHz) by the second-local oscillator (Upper heterodyne)
and is detected to generate an audio signal.
■ UHF accompanying circuit
Each band-pass filter is tuned to a target frequency
through the variable-capacitance Diode by the tuning volt-
age output from E-Volume (IC721) controlled with the Main
MCU (IC737).
D22,D23
D18,D19
Q358 Q3
XF351 D10,D11
49.950MHz
1st Local
A band
IC737
IC721
Main E-
MCU Volume
1st Local
B band
45.050MHz
Q359 XF352 Q1 D20,D21
D16,D17
D8,D9
D39,D41 UHF
Q6
D30,D31 Q10 BPF
AIP
Q14
SW
IC611
Sub
MCU
AIP
Q12
SW
Q5 D38,D40 Q9
D28,D29