TH-D72A/D72E
6
Figure 2-2 UHF receiver circuit
A band
AF
B band
AF
AGC
IC352
D352
SW
SW
SW
D351
AM
DET
IC351
Q352 Q354 Q356
455kHz
CF351
Q353
Q355
Q359
XF352
45.050MHz
Q1
1st Local
B band
D20,D21
D16,D17
D8,D9
Q5 D38,D40
D28,D29
Q9
Q12
AIP
SW
AIP
SW
Q14
IC611
Sub
MCU
IC721
E-
Volume
IC737
Main
MCU
UHF
BPF
Q10
D39,D41
D30,D31
Q6
D22,D23
D18,D19
D10,D11
Q3
XF351
49.950MHz
Q358
1st Local
A band
2nd Local
50.400MHz
2nd Local
45.505MHz
CF352
450kHz
IC353
A band demodulator
IC354
B band demodulator
DET
DET
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.
■
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).
CIRCUIT DESCRIPTION