Alinco DJ-G5, Руководство по обслуживанию

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3 Demodulation
3-1 L Band
After amplified in the first IF amplifier (Q78), the signal is fed to the demodulation
IC (IC302) Pin24. The first IF signal outputted to Pin24 (38.9MHz) is mixed in the
mixer of IC302 with the local signal of 38.455MHz which is oscillated in the
oscillation circuit of IC302 and the crystal oscillator (X303), then converted into the
second IF signal of 455kHz. The second IF is supplied from the IC302 Pin3. After
eliminating unwanted signal by the ceramic filter (FL302), the signal is applied to
Pin5 and Pin7.
As for the FM demodulation, the second IF signal applied to Pin7 is demodulated
in limiter amplifier and quadrature detection circuit of IC302 when IC302 Pinl4 is
open, and it is outputted from Pinl2 as the audio signal.
As for the AM demodulation, the second IF signal applied to Pin5 is demodulated
in AM amplifier and AM detection circuits of IC302 when the voltage of IC302
Pin14 is low, and it is outputted from Pinl3 as the audio signal.
3-2 R Band After amplified in the first IF amplifier (Q60), the signal is applied to the demodula­
tion lC301, Pinl6. It is mixed in the mixer of IC301 with the local signal of
45.555MHz which is oscillated in the oscillation circuit and the crystal oscillator
(X301) of IC301, then converted into the second IF signal of 455kHz. The second
IF is outputted from IC301 Pin3, and applied to Pin5 and Pin7 after eliminating
unwanted signal by the ceramic filter (FL30l).
4 Audio Circuit
4-1 FM (L band The audio signal supplied from IC302 is pre-emphasized white transmitting. So
the audio frequency should be compensated in the de-emphasis circuit (R366,
C363), then the signal is passed through FM/AM selection switch (IC303). The
frequency of 300Hz or below is cut in the audio high-pass fitter circuit (Q313), and
it is applied to the electronic volume (IC304) Pin1. The signal is passed through
the buffer (IC306), and adjusted the volume, then led to the audio power amplifier
(IC307) to drive the speaker.
4-2 AM (L bandWhen AM mode is selected, the switching transistor (Q312) is turned ON, and
IC302 Pin14 becomes low, then AM demodulation circuit of IC302 is activated.
The audio signal provided from IC302 Pin14 is passed through the de-emphasis
circuit (R362, C360), and FM/AM selection switch (IC303), then led to audio high­
pass filter circuit (Q313), electronic volume (IC304), buffer (IC306) and the audio
power amplifier (IC307) to drive the speaker.
Note:
The FM detection circuit in IC301 (TK10930) is operating even while AM receiving.
(The squelch circuit is activated by FM detection output.) So the FM audio is not
outputted by FM/AM selection switch (IC303).
4-3 FM (R band)
The audio signal supplied by IC301 Pin9 is compensated the audio frequency
characteristics in de-emphasis circuit (R330, C327), and the signal is passed
through the audio high-pass filter (Q306), then applied to the electronic volume
(IC304) Pin20. It is passed through the buffer (IC305), and led to the audio power
amplifier (IC307) to drive the speaker.
5 Squelch Circuit
5-1 L Band
A part of the audio signal of IC302 Pin12 is selected and amplified by the noise
amplifiers in R351 , R352, R350, R353, C351, C352, C353, and IC302. Then it is
supplied from IC302 Pin20 to be amplified again in the noise amplifier (Q309). The
amplified noise factor is rectified in D302, adjusted the level in VR303, and applied
to CPU (IC508) Pin96, then converted to the digital signal.
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