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LC notch filter not working!

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!!

Reply to
mrhyde377
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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?

Reply to
Anthony Fremont

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

Reply to
Michael Black

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.

Reply to
Anthony Fremont

Try this: (View in Courier)

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

--
JF
Reply to
John Fields

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