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Registered Member #816
Joined: Sun Jun 03 2007, 07:29PM
Location:
Posts: 156
Looks like your exiting your tuned circuit at harmonics of the signal gen frequency. At 12Khz I can see 3 peeks in one cycle. From the values I made the F0 to be 35.3Khz which if you divide by 3 is 11.7khz close to 12khz.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Yes, a square wave has odd harmonics, so you are exciting the response of the filter at 3x, 5x etc. your driving frequency. Switch to sine wave and your output will be sine as well.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Dr. Dark Current wrote ...
Yes, a square wave has odd harmonics, so you are exciting the response of the filter at 3x, 5x etc. your driving frequency. Switch to sine wave and your output will be sine as well.
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
Is the other wave in your scope pictures is the input waveform? It doesn't look like a very nice sine wave. When you are around 13 kHz, the significant third harmonic content of your "sine" is passed through the filter. Some of the fundamental also gets through the filter at this frequency, and these two signals mixed form what you see between 10 and 14 kHz.
In the future, I would suggest adding a diagram with the complete test setup and labeling the waveforms to show where in the circuit the measurements were made. To you it might be obvious, since you have the setup in front of you, but we can only guess from the limited amount of info posted.
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