No Full Stereo Seperation ..????

[xitronics]

Hello Guys..!

i had designed a stereo coder based on the convetional L and R switching concept... 76 Khz was produced with 4060 oscillator by using a rare 4.864 mhz crystal...

L, R switching is with the help of 4066 IC by using two 38 khz opposite waveforms generated by 4013 freq. divider.. Pilot tone was filtered using 19 khz 4th order passive RC lowpass filter (R = 8.2K, C = 1nF)..

i didnt use any bandpass filter for filtering of the composite L R signal.. as i wanted complete stereo seperation first.. even if my Tx o/p power had been wasted by unnecessary harmonics..

At my stereo FM, got the stereo seperation... but not adequate. Atmost the seperation might be 30db.. The left channel can be clearly heard in the right(although with considerably less intensity)..

Can anyone guess the problem.???

___________________________
Prasanna Rao..
India

 

[Frank Berry]

Your 19 kHz pilot must be exactly in phase with the 38 kHz subcarrier. It's also critical that the duty cycle of your 38 kHz switching frequency be exactly 50%.

 

[xitronics]

i doubt about the duty cycle of 4060 IC... But i have heard that it provides almost near 50% duty cycle..

the pilot lowpass filter provides 360 deg. phase diff but that should be the problem as 180, 360, 540 ... deg lags should be alright for seperation ..

_____________
Prasanna