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FM/AM
In the receiving side of FM/AM the signal of 38.85MHz is selected by crystal filter XF101. Then the signal is amplified at the 1st IF amplifier Q112 after eliminating the adjacent channel signal.
WFM
In the receiving side of WFM the signal of 38.85MHz is selected by band-pass filter. Then the signal is amplified at the 1st IF amplifier Q112 after eliminating the adjacent channel signal.
4. IF FM/AM
The amplified signal at the 1st IF amplifier Q112 is led to the demodulator pin 24 of IC105. The signal of 12.8MHz from the reference buffer output of IC101 is multiplied by 3 in Q133. Then the signal is mixed with the signal of pin 1 of IC105 in the mixer circuit inside of IC105 and converted into the 2nd IF signal of 450kHz. The converted 2nd IF signal is output from pin 3 of IC105.
FM
The output signal from pin 3 of IC105 is led to pin 7 of IC105 after eliminating the adjacent channel signal at the ceramic filter FL103. The input 2nd IF signal to pin 7 of IC105 is demodulated at the limiter amplifier and quadrature detector circuits inside of IC105, then output from pin 12 of IC105 as an AF signal.
AM
The output signal from pin 3 of IC105 is led to the pin 5 of IC105 after eliminating the adjacent channel signal at the ceramic filter FL103. The 2nd IF signal input to pin 5 of IC105 is AM-demodulated inside of IC and output from pin 13 of IC105 as an AF signal. The 1st IF amplifier Q112 is controlled by reverse AGC at AGC amplifier Q117 to get better audio output even though the input is changed, and the gain is controlled.
WFM
The output signal from pin 3 of IC105 is led to pin 7 of IC105. The input 2nd IF signal to pin 7 of IC105 is demodulated at the limiter amplifier and quadrature detector circuits inside of IC, then output from pin 12 of IC105 as an AF signal.
5. Squelch
The AF signal got from pin 12 of IC105 is fed to pin 19 of IC105. The input signal is output from pin 21 of IC105 passing through the noise filter amplifier and rectifier circuits inside of IC. The rectified signal is added to the A/D port of the microcomputer IC1. Judging the signal, the microcomputer controls ON/OFF of the audio output.
