Coil winding info

Kludge wh7hg.hi at GMAIL.COM
Sun Nov 7 19:05:22 EST 2010

-----Original Message-----
From: ka9egw at [mailto:ka9egw at] 
> 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. 

This is good to know.  It's something I hadn't thought of.

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

In the case of basket weave and honeycomb coils, the only place I can see
this as making a difference is in the overall height of the coil.  In both
of these cases, the capacitance et al between immediately adjacent turns are
vastly reduced since there are no immediately adjacent turns except at the
corners.  What assumptions does Prof. Coyle make and can they be adjusted in
the formulae?

> Also Professor Coyle is approximating the basket weave coil as a solenoid
> order to make it work with Wheeler's solenoid formula. This may not be a
> assumption as long as the difference between inner and outer diameter is
> less than about 10% of the inner diameter. 

Let's see ... a 1-1/2" inside diameter with 1/16" forming pegs.  Nah,

This eliminates honeycomb coils entirely since their outer diameter is at
least 50% over 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. 

In a complex coil like the mixed "over & under" basket weave ones or
honeycomb coils, this may have to be calculated by actually winding until
the pattern starts repeating.  Then count the number of turns that took and
the length of the wire needed to do it.  Some of the oddball coils (inverted
truncated cones, for example) I made way back when under my mentors'
tutelage were more by guess and by golly but they worked.  (There was reason
for doing this but I don't remember what it was.  They were interesting,
though.)  I suspect that these would have been fairly easy to calculate
using this method if I had thought about it some.

While I've pretty much abandoned the 1920s projects, some of the older
non-solenoid type coils will wind up in the 1930s projects, more because I
like them rather than for any historic reasons.  This info on Prof. Coyle
will help immensely.  Thanks.

Best regards,
Michael, WH7HG BL01xh 
Hiki Nô! 

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