Re: Wire length, coil geometry, and velocity factor

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Paul Nicholson" <paul-at-abelian.demon.co.uk> 

Mike wrote:
 > has anyone looked at a coil who's H/D ration is 0.3?
 > From what I have calculated, the quarter wave frequecy
 > would be very close to the LC frequency at that geometry,
 > with no topload.

It would be a reasonable extrapolation from existing measurements
to conclude that unity velocity factor (which is what I assume
you mean) would be achieved somewhere down in that area, so
you may well be right Mike.

The lowest h/d measured by tssp is 0.91 - this was a special coil
wound with taps for current measurements,

  http://www.abelian.demon.co.uk/tssp/tfcp260302/

Average diameter = 10.915 inches, overall length = 9.92 inches.

Wire length is ~= 385 metres, a distance which is a free-space
quarter wavelength at 300e6/385/4 = 195kHz.  The fundamental
resonance of the coil was measured to be 229.9 Khz, giving a
velocity factor of 229.9/195 ~= 1.18

Malcolm supplied measurements for h/d=17.5, and obtained a
velocity factor 2.37, which is the current record holder for
the large h/d end of the scale.

I wrote:
 > Malcolm measured 1.0697MHz, the formula predicts 1039.6Mhz*

Terry wrote:
 > >> * I am sure Paul meant 1.0396Mhz - Terry <<

I did, thanks.

 > I have a long skinny coil here...

Perhaps we can look forward to some measurements.

In a recent thread in which I asked about Ed Harris,
Ed Phillips wrote:

 > Was Ed Harris the guy who gave us some neat simulation programs?

I think he did contribute some software.

 > They're probably on this machine but I don't know where and
 > don't remember what they did except that I was impressed.

I've been impressed with Ed Harris's various posts.  Lots of the
stuff we talk about these days was discussed by Ed Harris on this
list nearly 10 years ago, but the ideas didn't appear to take root
at the time.   He seemed to be struggling against the pathological
'theory is a waste of time' attitude which prevailed at the time.

Wonder if there's any TCBA articles which discuss how velocity
factor varies with h/d ratio - I'll have to have a browse through
the index.
--
Paul Nicholson
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