TH-D72A/D72E
5
3. Receiver System
3-1. VHF receiver circuit
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A band VHF receiver circuit
The reception signal from the antenna passes through a
fi lter circuit and goes to the RF amplifi er (Q11). 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 (Q7) and passed through the band-pass fi l-
ter before entering the mixer (Q2). The signal converted by
the fi rst-local oscillator (Upper 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.
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B band VHF receiver circuit
The reception signal from the antenna passes through a
fi lter circuit and goes to the RF amplifi er (Q13). 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 (Q8) and passed through the band-pass fi l-
ter before entering the mixer (Q4). The signal converted by
the fi rst-local oscillator (Upper 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 hetero-
dyne) and is detected to generate an audio signal.
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VHF 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).
Figure 2-1 VHF 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
Q4
1st Local
B band
D26,D27
D14,D15
Q8 D44,D45
D35,D36
Q13
Q16
AIP
SW
AIP
SW
Q15
IC611
Sub
MCU
IC721
E-
Volume
IC737
Main
MCU
VHF
BPF
Q11
D42,D43
D32,D33
Q7
D24,D25
D12,D13
Q2
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
CIRCUIT DESCRIPTION