Receiver System - Kenwood TH-D72A Service Manual

3. Receiver System

3-1. VHF receiver circuit
■ 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.
IC353
A band demodulator
A band
AF
IC352
B band
D352
SW
AF
SW
IC351
D351
AM
AGC
DET
CIRCUIT DESCRIPTION
CF352
2nd Local
50.400MHz
450kHz
DET
2nd Local
IC354 45.505MHz
B band demodulator
DET
Q352 Q354 Q356
CF351
455kHz
Q353
SW
Q355
Figure 2-1 VHF receiver circuit
TH-D72A/D72E
■ 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.
■ 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).
D24,D25
Q358 Q2
XF351 D12,D13
49.950MHz
1st Local
A band
IC737
IC721
Main E-
MCU Volume
1st Local
B band
45.050MHz
Q359 XF352 Q4 D26,D27
D14,D15
D42,D43 VHF
Q7
D32,D33 Q11 BPF
AIP
Q15
SW
IC611
Sub
MCU
AIP
Q16
SW
Q8 D44,D45 Q13
D35,D36
5