MC1496 STEREO CODER |
Summary description:
L-R DSB 38KHz signal is obtained with MC1496 modulator. Use 10K/1% resistors around of L-R operational amplifier.
The oscillator uses a 455KHz ceramic resonator and two dividers, in this way is possible to generate 19KHz and 38KHz. One trimmer capacitor connected in series with 455KHz resonator, help to increase the frequency up to 456KHz.
L+R signal are added (mixed) together by two resistors. For best result, the stereo audio signal must to be processed using a 15KHz LPF. Checks download section to see a good audio LPF.
The stereo encoder is provided with RDS input and 19KHz output for phase synchronization.
Stereo separation is good. For best result, MC1496 must not be overloaded. Check also if 38KHz is clean and has correct amplitude.
Pilot signal 19KHz need to have low amplitude, only 10% from maximum value of MPX signal. Use "pilot level" variable resistor to adjust 19KHz level. The mono/stereo switch is connect in series with 19KHz pilot signal.
All TL082 operational amplifiers can be replaced with TL072 or better type.
MC1496 Modulator
Oscillator 19KHz and 38 KHz
15KHz Lowpass filter with pre-emphasis