Keith Dysart wrote:
When I look at one of those coils, I think it is one big complicated
mess of distributed capacitance and inductance. There is intra and
inter turn capacitance and capacitance to ground. A mess.

Some say such a coil can be adequately modelled using a lumped
inductor.

I'm afraid you have fallen for someone else's mis-statement of that
point of view.

The most recent posting about lumped inductance was probably mine. It
states both the value and the limitations of this approach.

"Lumped inductance is often a good approximation to reality, so [most
models other than Cecil's] very sensibly use that as their
starting-point. Then they can progressively apply corrections for the
distributed properties of a real-life inductors. The smaller those
corrections are, the simpler the model becomes.

In practical terms, a lumped-inductance model will take you straight to
a buildable prototype. The necessary corrections can then be applied by
mechanical adjustment, without needing to model the distributed
properties of the loading coil in detail. Such models are to be found in
G4FGQ's MIDLOAD program, ON4UN's 'Antennas for Low Band DXing' and other
handbooks.

There was also an excellent theoretical treatment by Boyer in 'Ham
Radio', which shows in detail how the model of an antenna as an
unterminated transmission line is COMPLETELY capable of incorporating
lumped inductance."



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek