Interesting. I don't have this book handy [all I have is my signed
copy of "Antennas, 2ed" ]. Is there any indication in the text as
to where the "actual current" data came from? Is it derived from
some sort of EM analysis, or is it measured data I wonder?
I think Kraus spent a lot of time studying helical structures
while he was developing the helical antenna. Since a loading
coil is basically a helical antenna operating in the normal mode
perhaps the answer to this question lies in some of his early
work.

Thanks,

Mike, W4EF.............................................. .........


"Cecil Moore" wrote in message
...
Michael Tope wrote:
This is what bothers me about the claims that the "cosine law"
can be used to predict the current taper in the loading coil.

It is certainly NOT a "cosine law". It is at best an approximation.
From _Antennas_For_All_Applications_ by Kraus & Marhefka, third
edition, page 464: "The difference between these (dashed) curves
and the solid curves is not large but is appreciable." The solid
curves are cosine curves. The dashed curves, indicating the actual
current, are not cosine curves but are relatively close approximations.

The only time pure cosine curves will result for net current is in
a lossless situation which is certainly not entirely valid or accurate
for a radiating antenna.

If the magnitudes of the forward current and reflected currents are
not equal, there will be a drift away from a pure cosine shape.
--
73, Cecil http://www.qsl.net/w5dxp