LC notch filter not working!

Apr 26, 2007 4 Replies
M

Hi,



I am trying to filter out a 13.56 MHz signal (and if possible I would want to filter some of its harmonics in succeeding circuits).



I have tried a LC parallel resonance circuit put in series with the load. In theory the impedance of the LC parallel circuit becomes infinite at resonance frequency, i.e. the circuit becomes open.



I used a fixed inductance L=10uH and a variable C, i.e. a trimmer to get the product L*C = 1 / (2*pi*13.56MHz)^2 right. C should be approx 14 pF, however, due to +/-20% tolerances in L, I use a trimmer.



However, I can turn the trimmer (in the range from 10 to 20pF) as much as I want and I don't see ANY effect at all on my scope.



Any hints ? What am I missing ?



I have also looked at active notch filters, but this seems to be rather difficult at these high frequencies (see

formatting link



Thank you!!



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A

Please learn to cross-post, it makes everyone's life easier when you want to cover the topic in more than one group.

What kind of termination do you have on the filter?

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M

Well no.

Learn to figure out the most appropriate newsgroup, and post there. There is rarely any good reason to cross-post, it is usually the sign of someone too lazy to find the best place, or too clueless.

Just because cross-posting is better than multiple posting does not make cross-posting a good thing. It's just better than multiple posting.

And multiple posting is just as much a mark of laziness or cluelessness as cross-posting.

This is a .basic question, not a .design question (I assume that's where else the guy posted to, you and the rest have made it such a cesspool with your cross-posting and non-beginner questions in there that I have stopped reading it).

ANd once again, Mark Zenier's guide to the sci.electronics.* hierarchy explains, including a bit about how cross-posting is better than multiple-posting, but not by much: ftp://ftp.eskimo.com/u/m/mzenier/seguide9706.txt

Michael

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A

Oh gawd here we go again. :-( Are you a person or a bot? Look, I don't care what your opinion on this matter is. I don't know how to make it any more clear Michael, but GFY comes to mind.

Do you have anything TECHNICAL *OR* ON TOPIC to add to this thread?

I really hadn't noticed you missing, but then you don't offer much in the way of technical stuff anyway. The cesspool that exists there now is primarily a result of trolls and netkops like yourself, not from people x-posting electronics questions.

So you consider LC filters and reactive impedance a .basics thing huh? If so, why don't you add something since we're here?

Have you actually bothered to read it yet? I certainly have. Building/debugging LC filters *do* constitute design AND x-posting is ok in this context, should I post the appropriate excerpts?

After seeing MZ himself tell you to give it a rest, I figured you would stop with this. I guess I figured wrong. You're not going to change my beliefs on this matter, so can't you just PLEASE give it a rest? OTOH if I'm still not making myself clear, I'll be happy to choose verbiage more to the point.

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J

Try this: (View in Courier)

VIN>-----+---->VOUT | [L] | [C] | GND>-----+---->GND

JF
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