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G0FTD > COILS 28.12.05 00:59l 64 Lines 1659 Bytes #999 (0) @ WW
BID : 503194G0FTD
Read: GUEST DL1LCA OE7FMI
Subj: Further tests done
Path: DB0FHN<DB0RGB<DB0MRW<DB0SON<DB0ERF<DB0FBB<DB0BI<DB0NOS<DB0EA<DB0RES<
ON0BEL<ZL2BAU<GB7YKS<GB7SYP<GB7PFD<GB7ESX<GB7NNA
Sent: 051227/1420z @:GB7NNA.#31.GBR.EU #:75979 $:503194G0FTD [Witham, Esx]NNA
I previously wrote:
> G0TSU wrote:-
>> The small diameter of the core would indeed be effective
>
> It seems so.
>
> I just did a quick experiment:
>
> I took one coil of wire wound on a 35mm former and then inserted a
> much smaller diameter (about 8mm) piece of ferrite rod in the middle off
> it.
>
> The 19uH shot up to 45uH.
>
> The I just held the same ferrite rod upto the *outside* of the coil
> but the effect was minimal - about 0.3uH.
>
> I've drawn two ascii drawings below to help demonstrate.
>
>
>
> .-'"""'-.
> .' '.
> / \
> ; xx ; [Ferrite inside much smaller than coil diamter]
> ; xx ;
> \ /
> '. .'
> '.......-'
>
>
>
> xx
> xx
> .-'"""'-.
> .' '.
> / \
> ; ;
> ; ; [Ferrite held against ouside of coil]
> \ /
> '. .'
> '.......-'
>
>
>
>
> The next test is to find some brass rod to see if I can lower the value
> which is what I really need to do.
Now I've just found some brass rod which is 10mm diameter compared to
the test inductance being 35mm diameter.
Inserting the 10mm brass rod sent a 19uH down to 18uH which is of limited
use.
I suspect that having a core closer to the coil diameter is the most
effective, however it does show that even if the core is much smaller
diameter it does have some effect.
Oh well that kept me amused for half an hour ;-)
- Andy -
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