Standart HX290U, Руководство по обслуживанию

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5
2.2.4 Second IF Circuit
The second IF IC comprises a second local oscillator,
second mixer, second IF amplifier, wave detector, noise
amplifier, and noise wave detector.
The first IF signal passes through pin 16 of second IF IC
QH04 and is input to the second mixer built into QH04.
The first IF signal and second local signal are mixed, and
the first IF signal is converted into a 455 kHz second IF
signal. After having adjacent signal elements eliminated
by ceramic filter FH05 (6 dB bandwidth ±6.0 kHz or
greater), the second IF signal is converted into an audio
signal by the second IF amplifier and a quadrature wave
detector.
9 8
5 3
32
12 14
QM01
QA01
TA7368F
Second IF IC
QH04
TA31136FN
De-emphasis circuit
CH23, RH14, CH21, RH22
CH22, RH12, RH13, CH30
Band pass filter
audio signal
First IF signal
First IF amplifier
squelch signal
Quadrature wave
detector
1
Second
mixer
Second local
oscillator
Crystal
resonator
Ceramic filter
(6dB bandwidth
±
6 kHz or greater)
Second local signal
(44.495 MHz)
Second IF
amplifier
Noise
amplifier
Noise wave
detector
Microprocessor
AF power amplifier
16
XH01
44.495 MHz
FH05
455 kHz
QL02
QH03-2SC4649
Inverter
amplifier
(Approx. 6 dB amp)
Figure 2-3 Second IF circuit block diagram
2.2.5 Audio Circuit
The frequency of a portion of the audio signal is corrected
by the de-emphasis circuit built into base band IC QM01.
After this, the audio signal is amplified by approximately 6
dB by AF amplifier built into QM01. After passing through
AF mute switch QM02, the audio signal is input to pin 4 of
AF power amplifier QA01.
The audio signal is amplified to approximately 0.5 W by
QA01.
RA01
volume
14
65
32
10
Second IF IC
0.5W
Speaker
EL01
Ext. speaker jack
3.5 DIA.
JA01
4
Base band IC
AF power amplifier
Audio signal
Squelch signal
Microprocessor
AF mute switch
QM01
AK2342A
QL02
QH04
TA31136FN
QA01
TA7368F
ON
OFF
OFF
ON
QL02 QM02 Squelch operation
Pin 65 Hi output
Pin 65 Lo output
QM02
HN1K02FU
(Approx. 6 dB amp)
Figure 2-4 Audio circuit block diagram