DJ-C1 CIRCUIT DESCRIPTION
1) Reception
1. Front End
The signal picked up by the antenna is passed through a low-pass filter and
band-pass filter, and amplified by an RF amplifier (Q207). It is then passed
through another low-pass filter and sent to the mixer (Q209).
2. Mixer
The mixer (Q209) creates the sum and difference of the received signal and
the first local signal The crystal filtter (XF201) selects the 21.7 MHz signal and
eliminates adjacent signals. The first IF amplifier (Q210) then amplifies the
selected signal. The upper side local signal is used as the first local signal It is
obtained by passing the signal from the VCO through two buffer amplifiers
(Q204 and Q208) and into the base of the mixer (Q209).
3.IF
The signal amplified by the first IF amplifier (Q210) is input to pin 16 of the
demodulator circuit (IC207). A second local signal of 21 ,25 MHz is oscillated
by the crystal(X201) and IC202, and is input to pin 1 of the IC207. These two
signals are mixed by the demodulator's internal mixer and converted to a 450
kHz second IF signal. The converted second IF signal is output from pin 3 of
IC207 to a ceramic filter (FL201) where adjacent signals are eliminated. The
resulting signal is then sent back to pin 5 of IC207.
[FM]
The second IF signal input to pin 5 of IC207 is demodulated by the internal
limiter amplifier and quadrature detection circuit. It is then output as an audio
signal from pin 9.
[AM]
For AM, the S-meter output from pin 12 of IC207 is amplified by the AM audio
amplifier (Q220). Also, the AGC amplifier (Q221 ) forward-controls gain of the
first IF amplifier (Q210) in order that the correct audio signal is obtained even
when the input signal changes.
4. Squelch
The squelch takes white noise from pin 9 of IC207 and inputs into pin 8 of
IC207. The noise passes through an internal noise filtter amplifier and rectifier
circuit, and is output from pin 14. The rectified voltage is input to the A/D port
of the microcomputer (IC101 ). The microcomputer turns audio output ON/OFF
based on this voltage:
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Summary of Contents for DJ-C1
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Page 17: ...EXPLODED VIEW 17 ...
Page 18: ...EA61 ...
Page 25: ...PC BOARD VIEW CPU Unit side A DJ C1 CPU Unit side A DJ C1 27 ...
Page 26: ...CPU Unit side A DJ C4 CPU Unit side B DJ C4 28 ...
Page 27: ...MAIN Unit side A DJ C1 29 ...
Page 28: ...MAIN Unit side B DJ C1 30 ...
Page 29: ...MAIN Unit side A DJ C4 31 ...
Page 30: ...MAIN Unit side B DJ C4 32 ...
Page 31: ...PTT Unit side A DJ C1 PTT Unit side B DJ C1 PTT Unit side A DJ C4 PTT Unit side B DJ C4 33 ...
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