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From: john larkin <jlArbor.com>
Newsgroups: sci.electronics.design
Subject: Re: those coupled drum core inductors
Date: Sun, 16 Mar 2025 14:20:18 -0700
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On Sun, 16 Mar 2025 20:53:32 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:

>Jeroen Belleman <jeroen@nospam.please> wrote:
>
>> On 3/16/25 15:15, john larkin wrote:
>> > 
>> > 
>> > https://www.dropbox.com/scl/fi/cd8gxmlrar3kvv3iz36xe/Mu_twin.jpg?rlkey=d
>> > vl8e7fbtjnzz3l9q9urkyyfn&raw=1
>> > 
>> > https://www.dropbox.com/scl/fi/nm1ksdn7eufm90ol0b0ec/Murata_Coupled_1.jp
>> > g?rlkey=e7yvk464xupz4axy7lt6zj3zk&raw=1
>> > 
>> > I was surprised to get K=0.6 by just putting them along side.
>> > 
>> 
>> That's somewhat surprising, indeed. Are the cores dumbbell-shaped? Does
>> the coupling vary steeply with the spacing?

The inductors are covered by shrink tubing but seem to be tall skinny
drum cores, dumbbells.

>
>
>Stick a sig-gen across one and a 'scope across t'other, that will tell
>you how much coupling there is at any given spacing.

I've done that but didn't quantify coupling vs distance. I measured
coupling and series inductance assuming two parts mounted as close to
one another as makes sense, not quite mechanically interfering.

I used a third one as a mag field probe, to verify that the series
pair has a magnetic null plane between the parts, and doesn't couple
far-field very much.

The extra 6 mH helps my circuit a bit, without adding ESR. Cute trick.

I guess there could be other uses for this coupling.