Mike Coslo wrote:
Roy Lewallen wrote:

That this concept is wrong can and has been shown by theory, modeling,
and measurement. I made and posted measurements on this newsgroup in
November 2003 which demonstrated clearly that the presumption is false.

Okay. It looks like we have at least some measurements that differ.
Any idea why that would be?

The amount the magnitude of the current drops across an inductor is
determined primarily by the amount of inductance and the capacitance
from the inductor to ground or the other half of the antenna. This is
easily explained by simple lumped constant circuit theory. There's also
some variation due to radiation and imperfect coupling between turns. In
the extreme case of a very loose helix, coupling is poor and radiation
is high, so the helix acts more like a wire than an inductance. This
requires a more complex analysis, but that's also in the realm of well
known phenomena. With this wide variation in physical possibilities,
different results can't be avoided. What some of us have tried to do is
explain why the results occur.

I don't know of differing results from the same physical setup, but it
could surely happen. Making good measurements isn't a trivial task.

Do you remember the name of the thread?

Current in antenna loading coils controversy (long). I made two sets of
measurements. The second was posted on Nov. 11, 2003 and the first a few
days earlier.

The loading coil isn't making the antenna act like a physically longer
antenna. In the extreme case of a physically short inductor at the
feedpoint, it's simply modifying the feedpoint impedance and has no
effect whatever on the antenna's radiation.

Would the inductor then be best right past the feedpoint? Certainly
having the inductor at the far end, or in the middle seems like a bad
place for it. (not talking about trap antennas)

Generally not, but it depends on several factors. Moving the coil upward
increases the radiation resistance of the system, which improves
efficiency in the presence of ground loss. However, it also requires a
larger coil, so the coil's resistance is greater. But the current at the
location of the coil is lower, so overall I^R loss of the coil is often
less with the coil somewhere around halfway up. The relative amount of
coil and ground loss, as well as the amount of top loading if any, are
all factors in determining which position is best. This is really a
separate question, and I don't have varied enough experience with HF
mobile setups to be anywhere near an expert. Tom, W8JI, is though. You
can take what he says on the subject to the bank.

Roy Lewallen, W7EL

Roy Lewallen wrote:
The amount the magnitude of the current drops across an inductor is
determined primarily by the amount of inductance and the capacitance
from the inductor to ground or the other half of the antenna. This is
easily explained by simple lumped constant circuit theory.

How does lumped constand circuit theory handle the phase shift through
the inductance? It is certainly NOT zero as your measured.
--
73, Cecil http://www.qsl.net/w5dxp