[HomeBrew] notch filter

[Jim Kearman]

Richard: Try isolating the poles and testing them separately. If you built it as described the second pole should short the signal, so I'd start there. The others should appear as a high Z at the frequency. If you have a scope or rf voltmeter you should be able to confirm the poles are working as designed (voltage dips across the second pole at resonance, and peaks at resonance on the other two) and perhaps find where the problem lies. 

After that, if no luck (which would surprise me) you could try sweeping the filter while measuring the output voltage, to get some idea of what it's actually doing. Maybe the notch is so sharp you're missing it? 

73,

Jim, KR1S
http://kr1s.kearman.com/