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K0CQ > COILS 16.09.05 19:46l 27 Lines 1063 Bytes #-6956 (0) @ WW
BID : 13112_W0AK
Read: GUEST DL1LCA OE7FMI
Subj: Re: Pile wound coil problem.
Path: DB0FHN<DB0FOR<DB0MRW<DB0SON<DB0HBN<DB0SWR<DK0WUE<7M3TJZ<SP7MGD<ZL2TZE<
WA7V<WH6IO<KJ6EO<W9BS<W9HU<KQ0I<W0AK
Sent: 050916/0143Z @:W0AK.#CIA.IA.USA.NOAM #:13112 [Des Moines] $:13112_W0AK
From: K0CQ@W0AK.#CIA.IA.USA.NOAM
To : COILS@WW
Check the self capacitance of the coil. Likely its a lot more in
the multilayered coil than the single layered coil and that
changes the apparent inductance.
That internal distributed capacitance can cause parts of the coil
to resonate below your measuring frequency and to really
complicate what you wish to be a simple coil.
Check the C it takes to resonate the coil at a low frequency, say
10 KHz, then check the C it takes at twice that low frequency.
You may see a difference from the factor of 4 C change it should
take if the coil wasn't contributing C. There is a formula in the
Boonton Q meter manual (which isn't turning up at the moment) to
compute the self capacitance of the coil from those two
measurements. You can do it graphically too by knowing the pure
inductance would take 4 times the C to tune at the low frequency
compared to the high frequency when the two frequencies are a
factor of 2 in ratio.
73, Jerry, K0CQ @ W0AK.#CIA.IA.USA
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