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G0FTD > COILS 27.12.05 14:27l 76 Lines 2175 Bytes #999 (0) @ WW
BID : 613190G0FTD
Read: DL1LCA GUEST OE7FMI
Subj: Re: Variable coil experiments ?
Path: DB0FHN<DB0THA<DB0ERF<DB0FBB<DB0IUZ<DB0GOS<DB0RES<DK0WUE<I0TVL<ED1ZAC<
GB7YKS<GB7SYP<GB7YFS<GB7LGS<GB7ESX<GB7NNA
Sent: 051227/1202z 75962@GB7NNA.#31.GBR.EU $:613190G0FTD [Witham, Esx]NNA V3.1
Hi Dem (and others who responded),
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.
Anyone who has seen my trolley mobile will have spotted my LF inductance
(see website below) wound on some waste pipe with a few 4mm plug taps
to alter the inductance. However on 160m I find that I need to be
ablwe to control the inductance value mopre accuratly and I was thinking
of having a sliding rod much like a dipstick arrangement.
.-"""""-.
/ 73's de \
.-. | _ _ | .-.
(_. '._ | |_\ /_| | _.' ._)
-._'-.(_ A _).-'_.-'
'-._| _____ |_.-'
_.-'_\`"""""`/_'-._
.-.-'_.-' `-----' '-._'-.-.
(,_.'` `'._,)
Colonel Andy
Supreme Commander of the Trolley Platoon
And The Laughter Corps
www.southgatearc.org/articles/g0ftd/shopping_trolley_wally.htm
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