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Old April 12th 06, 10:14 PM posted to rec.radio.amateur.antenna
Cecil Moore
 
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Default Current across the antenna loading coil - from scratch

Gene Fuller wrote:
I will retain the entire message below, so that I am not accused of
misattribution.


Gene, to the best of my knowledge, you have never
misattributed anything.

Where did you get this idea that the velocity factor is constant?


The equation for velocity factor includes coil diameter,
turns per inch, and wavelength. Keeping the coil diameter
constant, the turns per inch constant, and the wavelength
constant should ensure that the velocity factor is constant.

Specifically, why is the velocity factor of a resonant coil the same as
the velocity factor of a significantly shorter coil? It is pretty well
accepted that the inductance of coils does not scale linearly with the
length of the coil. Therefore any arguments about based on direct
calculation of Vf from L and C would seem to fail to support your model.


You are obviously mistaken. If you increase the L by lengthening
the coil, you have also increased the C by the same percentage.
The L and C for any unit length are the same no matter how long
the coil or transmission line is.

" . . . an approximation for M has been determined by Kandoian and
Sichak which is appropriate **for quarter-wave resonance** and is valid
for helices . . ."


Yes, but if one doesn't change the frequency or the diameter or
the turns per inch, the approximation should hold since nothing
in the VF equation changes by shortening the coil. One should be
able to shorten or lengthen the coil andmaintain the same VF.

Seems it is up to you to prove what you are saying. Please prove
that the ratio of L to C ratio of a coil changes with length. That
should be an interesting proof.
--
73, Cecil http://www.qsl.net/w5dxp
 
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