Coil winding info

Brian Sherwood Ka9Egw ka9egw at BRITEWERKZ.COM
Sun Nov 7 09:25:36 EST 2010

this from theradioboard web blog:
My own LCR meter does not give accurate readings due to a combination of
coil self-capacitance, and coil DC resistance.

But there are also some general problems with Professor Coyle.

It's important to bear in mind that Professor Coyle uses Wheeler's
inductance formula which is only accurate where the Length of the coil is
greater than .4 x Diameter. As the coils get shorter, the accuracy drops off
rapidly. One bit of information that hasn't been posted is the length
(height) of the coil. But, from the photos, it looks like this basket weave
coil is outside the range of accuracy for the formula.

Prof. Coyle also makes some assumptions about wire spacing which may not
always be valid.

Also Professor Coyle is approximating the basket weave coil as a solenoid in
order to make it work with Wheeler's solenoid formula. This may not be a bad
assumption as long as the difference between inner and outer diameter is
less than about 10% of the inner diameter. However this coil once again
falls outside that range, since the difference between inner and outer
diameter looks to be about 50% of the inner diameter. Generally, when an
oddly shaped coil is massaged to fit into an existing simple inductance
formula, the mean diameter should be calculated from the total length of
wire, and the number of turns. Dividing the total wire length by number of
turns gives you a mean circumference , and then dividing by pi, will give
you a mean diameter. This number generally gives better results in
inductance calculations than simply taking the average between inner and
outer diameter. Of course it means that you have to measure the length of
wire before you start winding, and then measure again after you finish so
that you can determine an accurate total winding length.

Since the coil in the photo appears to have a roughly square winding cross
section, the coil falls between a solenoid and a spider coil.
I would be inclined to use a formula for multilayer coils having a
rectangular winding cross section. It would probably be a better fit for
this shape of coil.

-----Original Message-----
From: Boat Anchor Owners and Collectors List
[mailto:BOATANCHORS at LISTS.TEMPE.GOV]On Behalf Of Kludge
Sent: Sunday, November 07, 2010 1:23 AM
Subject: Coil winding info

Somewhere along the line, I remember a site that had a calculator for
winding spider web, honeycomb, basket weave and other elder type coils only
I can’t remember where it is now.  If someone could point me to it, I would
be ever so grateful.


Best regards,

Michael, WH7HG BL01xh
Hiki Nô!

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