Background music decoder


Posted on Apr 11, 2012

A resistive voltage divider is used to establish a bias voltage for the input (Pins 2 and 3). The demodulated (multiplex) FM signal is fed to the input through a two-stage high-pass filter, both to effect capacitive coupling and to attenuate the strong signal of the regular channel. A total signal amplitude, between 80 mV and 300 mV, is required at the input. Its source should have an impedance of less than 10,000 ohm. The Phase-Locked Loop is tuned to 67 kHz with a 5000 ohm potentiometer, only approximate tuning is required since the loop will seek the signal. The demodulated output (Pin 7) passes through a three-stage low-pass filter to provide de-emphasis and attenuate the high-frequency noise which often accompanies SCA transmission.


Background music decoder
Click here to download the full size of the above Circuit.

Note that no capacitor is provided directly at Pin 7; thus, the circuit is operating as a first-order loop. The demodulated output signal is in the order of 50 mV and the frequency response extends to 7 kHz.




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

Simple PC smartcard reader
Cuckoo-song Generator
Five-transistor amplifier
Universal Laboratory Power Supply Circuit
200mW High Quality FM Transmitter With TX-200
emergency light circuit diagram
project DBS
coil coupled operation metal
1N5401 3.0 AMP Silicon Rectifier
RF drive audio oscillator



Top