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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 13th Jun 2021, 5:45 pm   #21
Radio Wrangler
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Default Re: Modifying an inductor?

Remember, your inductor is not a pure inductance, there is distributed stray capacitance amongst its turns. This distorts your inductance readings and apparent resonant frequencies, especially as you approach the self-resonance frequency. Modelling errors can get out of hand and rather counter-intuitive things appear to happen. 2-layer coils really make the capacitive effects worse. expecially if you laid the turns out there-and-back-again-over-the-top.

David
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Old 13th Jun 2021, 7:07 pm   #22
mole42uk
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Default Re: Modifying an inductor?

Yes, I sort of know about those unwanted capacitances. I just don't have any experience to know what to expect or how to design them into the filter. So I just work it out using what I do know, look up how some other people have done it, verify my idea with a design tool, check with someone on here who knows a lot more than I, then breadboard it and see what happens. So far I've been into several dead-ends, or learning experiences as I prefer, and have learned something about how LC filters function. What I haven't done yet is to achieve the design objective.....
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Old 13th Jun 2021, 9:03 pm   #23
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Default Re: Modifying an inductor?

Of course, I need a negative capacitor. Now, where’s my RS catalogue.....
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Old 13th Jun 2021, 10:52 pm   #24
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Default Re: Modifying an inductor?

Your inductor IS a negative capacitor!

Snag is its value changes with frequency. And you get free, stray, positive capacitors with it

David
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