Cec,

I thought you'd never ask. ;o)

Regarding solenoidal, single-layer, antenna loading coils -


Rule 1.

Inductance cannot change with frequency. With ANY coil, inductance between
the end points depends solely on dimensions and number of turns. As you
know, calculating formulae can be found almost anywhere. But to be very
exact with a long coil, an appreciable fraction of a wavelength, add the
inductance of a straight wire of the same length. After all, the coil may
consist of less than one turn as occurs when a coarse helix of wire is
pulled out straight. For a demonstration use program SOLNOID3. Read the
notes.


Rule 2.

Self-capacitance of a multi-turn, fairly close-wound coil consists of two
parts, Ca and Cb, both of which can be considered to be in shunt with the
coil to form a parallel tuned circuit. The structure does in fact behave
like this and has a measurable resonant frequency.


Ca is the same as the capacitance between the two halves of a dipole of the
same overall length and diameter as the coil. Matters become very
complicated as the spacing between turns increases


Cb is the capacitance between N adjacent turns ALL IN SERIES with each
other. So as N increases the resultant fast becomes very small. As spacing
between turns increases Cb decreases even faster. This is intuitively true.


All the above is calculable from dimensions. As is done in LOADCOIL and some
other programs. I'm sure somebody will let me know if a significant error
is found.


Sorry I am unable to provide references. I doubt if there are any. I have
made measurements.


Why not ask Yuri ? He sounds like an expert.
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.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
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"Cecil Moore" wrote
Reg, does your software involving loading coils take distributed
coil capacitance into account? Is there some rule of thumb involved?
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73, Cecil, W5DXP