Alinco DJ - C7 T, Service Manual

4 

4. IF

[FM/AM] 
The signal amplified at the 1st IF amplifier Q15 is supplied to pin 24 of IC7 
for demodulation. Also the signal of 12.6 MHz from the reference buffer 
output of IC2 is multiplied by 3 at Q12, and then it is led to pin 1 of IC7. 2 
input signals are mixed in the mixer circuit inside IC7 and converted into the 
2nd IF signal of 450kHz.The converted 2nd IF signal is output from pin 3 of 
IC7. 

[FM] 
The output signal from pin 3 of IC7 is led to pin 7 of IC7 after eliminating the 
adjacent channel signal at the ceramic filter FL3. The input 2nd IF signal to 
pin 7 of IC7 is demodulated at the limiter amplifier and quadrature detector 
circuits inside of IC7, then output from pin 12 of IC7 as an AF signal. 

[AM] 
The output signal from pin 3 of IC7 is led to the pin 5 of IC7 after eliminating 
the adjacent channel signal at the ceramic filter FL3. The 2nd IF signal input 
to pin 5 of IC7 is AM-demodulated inside of IC and output from pin 13 of 
IC7 as an AF signal. The 1st IF amplifier Q15 is controlled by reverse AGC at 
AGC amplifier Q19 to get better audio output even though the input is 
changed, and the gain is controlled. 

[WFM] 
The signal amplified at the 1st IF amplifier Q14 is supplied to pin 7 of IC7 for 
demodulation.  
The input 2nd IF signal to pin 7 of IC7 is demodulated at the limiter amplifier 
and quadrature detector circuits inside of IC7, then output from pin 12 of IC7 
as an AF signal. 

5. Squelch

The AF signal got from pin 12 of IC7 is fed to pin 19 of IC7. The input signal 
is output from pin 21 of IC7 passing through the noise filter amplifier and 
rectifier circuits inside of IC7. The rectified signal is added to the A/D port of 
the microcomputer IC6. Judging the signal, the microcomputer controls 
ON/OFF of the audio output. 

6. Audio

[FM/AM/WFM] 
The selection of receiving audio output signal between FM/WFM and AM is 
performed at IC8. The volume of output audio signal is adjusted at the 
electronic volume IC14 via the AF amplifier Q27. The signal is input to pin 2 
of audio power amplifier IC12 and output from pin 6 to drive a speaker, etc.