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VK3ABK > COILS 14.09.05 04:38l 29 Lines 1245 Bytes #999 (0) @ WW
BID : 4604_VK3BBS
Read: GUEST DL1LCA OE7FMI
Subj: Re: Pile wound coil problem.
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<7M3TJZ<ON4HU<N2BQF<VK3FIS<VK3BBS
Sent: 050912/0053Z @:VK3BBS.#MEL.VIC.AUS.OC #:4604 XFBB7.04h Bid:4604_VK3BBS
From: VK3ABK@VK3BBS.#MEL.VIC.AUS.OC
To : COILS@WW
Hello all.
The bulletins about coil winding, and resultant interwinding capacitance
which can cause resonance, and difficulty in measuring the impedance, have
concentrated on means for getting a true 'measured' value of inductance.
A parallel resistor (as proposed) will tend to swamp any resonance effect,
and so allow an impedance estimation. But this doesn't stop the inherent
resonances, as the interwinding capacitance is still present when the
inductor is used in a normal circuit configuration.
To overcome the problem, it's usual to 'scramble' (or jumble) wind the coil
instead of layer winding; or if an automatic coil winder is available, a
satisfactory professional looking 'honey-comb' coil can reduce interwinding
capacitance. Years ago I used an 'AVO' coil winder for various coil forms.
If a layer winding must be used, for space reasons for instance, metal film
inserted between windings (without forming a continuous turn, electrically)
and the film connected to a 'neutral' point will eliminate or greatly reduce
the unwanted capacity. Some impedance bridges have a 'guard terminal' for
this purpose, and it can be reproduced in the final circuit.
73. Dick. VK3ABK.
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