DJ-C4 CIRCUIT DESCRIPTION
1) Reception
The signal picked up by the antenna is passed through a how-pass filter and
1. Front End
amplified by an RF amplifier (Q207). It is then passed through a band-pass
filter, reamprlfied by Q209 and sent to the mixer (Q223).
2. Mixer
The mixer (Q223) creates the sum and difference of the received signal and
the first local signal. The crystal filter (XF201) selects the 21.7 MHz signal and
eliminates all other adjacent signals. The first IF amplifier (Q210) then
amplifies the selected signal. The lower side local signal (439.000 ~ 439.995
MHz only upper side) 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 (Q223).
3. IF
The signal amplified by the first IF amplifier (Q210) is input to pin 16 of the
demodulator circuit (IC206). A second local signal of 21.25 MHz is oscillated
by the crystal(X201) and IC202, and is input to pin 1 of the IC206. 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
IC206 to a ceramic filter (FL202) where adjacent signals are eliminated. The
resulting signal is then sent back to pin 5 of IC206. The second IF signal input
to pin 5 of IC206 is demodulated by the internal limiter amplifier and
quadrature detection circuit. It is then output as an audio signal from pin 9.
4. Squelch
The squelch takes white noise from pin 9 of IC206 and inputs into pin 8 of
IC206. The noise passes through an internal noise filter amplifier and rectifier
circuit, and is output from pin l4. 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.
5. Audio
Audio output is switched ON/OFF by Q219. Volume is controlled by Q224 and
Q225. The signal is input to pin 2 of the audio power amplifier (IC208) and
output from pin 6, thus producing sound from the earphones, etc.
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Summary of Contents for DJ-C1
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Page 17: ...EXPLODED VIEW 17 ...
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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 ...
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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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