"Walter Maxwell" wrote
Reg, I had never given much thought to the series relationship of
the
capacitance between turns. I had always considered them as being
in
parallel,
thus the honeycomb, or the basket-weave configurations to
minimize
the interturn
capacitance. Have I misconstrued the purpose of those
configurations?

Do I also understand you correctly that with a specified length
of
the solenoid,
and a given diameter, the total interturn capacitance is
independent
of the
number of turns, because the capacitance between turns adds in
series to the
same value regardless of the number of turns?

====================================
Walt,

As I said, I was referring only to the solenoid form.

Below the self-resonant frequency and for some way above it, the
distributed self-capacitance is equivalent to a lumped capacitor
across the ends of the coil.

Because capacitances between adjacent turns are in series with each
other, the capacitance between turns only matters when there are
only
one or two turns. So, for ordinary proportioned coils, when there
are
more than a few turns, the self-capacitance tends to become
independent of the number of turns, wire diameter and wire spacing.

The wire turns can be considered to form the outside of a Faraday
cage.

To calculate self capacitance, consider wire spacing to be zero.
When
isolated in space we have the capacitance between the two fat
halves
of a dipole. Which is calculable from length and diameter of the
coil,
and is equivalent to a lumped capacitance between its ends, which
may
be used to calculate the self-resonant frequency.

Or the self-resonant frequency can be calculated directly from
dimensions and number of turns.

In the past I have measured the self-resonant frequency of coils of
all sorts of dimensions. From antenna loading coils, coax choke
coils, to 6 feet long, 1 inch diameter, 1000 turns, 160-meter
helical
antennas. In all cases measurement results agree with the
calculating
formula within the uncertainties of the measured input data.
----
Reg.

=========================================
Thanks, Reg, for the valuable insight. It does pay to read the posts
made
by one G4FGQ.

Walt
=========================================
Walt,

Yes, there is only one G4FGQ. Although I confess I don't spend much
time on the air these days. Poor health!

When it comes to antennas, one reason why I don't publicise the source
code of my programs is that they are full of proven little tricks like
the foregoing which give answers in the right american ball-park.
There is always the danger that unjustified, unqualified criticism
would spoil the confidence and integrity to be placed in them by
novices. If for any reason you don't like a program you can always
have your money back!

One day I might list my 60 years of engineering experience but it may
be construed as bragging.

And a compliment from you, Walt, is a compliment indeed!
----
Reg.