Owen Duffy wrote in
:

....
You have to view the helix as a transmission line.

I mightn't have spelled this out fully.

A 15m straight length of wire could be viewed as a transmission line.

Coiling the wire into the form that Tom measured changes the transmission
line characteristics. Corum's paper and his references deal with
development of parameters for the new transmission line.

Corum argues that solving this new transmission line is a better method
of determining the inductance of the coil that other methods. That
probably understates it a bit, because he represents that his method is a
better way of estimating self resonance, better than the notion of a
lumped parasitic capacitance to deal with distributed capacitance
(another transmission line attribute).

Estimating inductance has been a challenge over a long time.

Corum's method with some extensions is incorporated in the online
calculator to which I gave a link. I have used this calculator to a
limited extent, and it has reconciled well with measured values. My
observations don't prove that it is accurate, but they haven't proved it
grossly inaccurate, and so far, it seems a good estimator for the types
of problems I have solved.

I must admit that I haven't tried solving inductance using David Knights
approach, it may well work and looks to be a degree simpler, but it
doesn't seem to deal with the distributed capacitance /self resonance
issue. One of my to-do jobs is to knock up a calculator and compare both
solutions to some measured values... which is something of a problem for
me because I mainly depend on others for quality measurements.

This issue has held up further work on bootstrap coax traps
(http://www.vk1od.net/coaxtrap/index.htm) . After a lot of work modelling
one of my correspondent's traps, he didn't want the analysis published
because it disagreed with his QEX article. A later QEX article supports
my model. Ah, that's ham radio!

I see people quoting the late Reggie's tools, but unfortunately he did
not expose the underlying algorithms to most of them, so they are a bit
of an unknown quantity in that respect.

I digressed a bit there, but estimating inductance remains a great
interest for RF practitioners.

Owen