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Old April 10th 06, 11:32 PM posted to rec.radio.amateur.antenna
 
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Default Current across the antenna loading coil - from scratch


Yuri Blanarovich wrote:
Check my article that describes the controversy, shows some proof of reality
and then efforts of the "gurus" to deny it and "reason" why it can't be so.
http://www.k3bu.us/loadingcoils.htm


Yuri,

I know you aren't going to like to hear this, but your article
incorrectly claims the current difference (you call it current drop) is
related to the electrical degrees the coil replaces.
That is not accurate.

ON4UN's book was initially incorrect.

Consider a short vertical antenna. If the current is uniform through
toploading, radiation resistance is higher and current lower throughout
the radiator.

If it is base loaded, current becomes nearly triangular in
distribution. Current into the vertical actually doubles so we have the
same number of ampere-feet. It always requires the same number of
ampere feet to radiate the same power as EM radiation.

The job of the inductor in either system is simply power factor
correction, to bring voltage and current into phase. We have a large
voltage drop across the coil, but current does not change. phase shift
and delay of current through the inductor will also be very small, zero
in a perfect coil.

That is in an ideal antenna with very small stray capacitance to the
outside world compared to the antenna area above the coil.

If we have a physically large coil, the coil MIGHT have significant
capacitance compared to the antenna area above the coil. In this case
there would be a difference in current between the bottom and top
terminal of the coil, and there would be phase difference in the
current entering and leaving the coil, but it is a result of current
being shunted off through displacement currents.

The exact amount would depend on the physical size of the coil and the
capacitance compared to the antenna above the coil.

There is not any magic to any of this, and we don't need to have
standing waves. It is incorrect to consider the coil behavior and
antenna currents by making the coil "act like" it has the missing
electrical dgrees or replaces a section current curve in the antenna.

I can have one antenna and use a good coil design that has essentially
no current difference at each terminal, and replace it with a very
large (or poorly designed) diameter coil that has large differences in
current at each end. Probably the ultimate in poor coil design for base
loading is a linear loading system or stub, while the best would be a
compact coil with nearly equal diameter to length.

The very fact we can change distribution all over the place with only a
change in loading inductor design proves your theory incorrect.

Please try to not extract certain sentences from long explainations to
distort the overall picture of what really happens, and of what I am
describing.

The fact is, we cannot model or predict the behavior of a loading
system without knowing the displacement currents. Neither wave theory
nor "missing antenna length" theory will paint the correct picture of
what is going on, and neither will give an accurate answer to a wide
variety of real world systems.

By the way, this did not start with Belrose and it is not a QST or
Handbook problem. The Antenna Engineering Handbook by Jasik and dozens
of other college or engineering textbooks all deal with the problems
the same way. If you are looking to libel anyone, you need to go all
the way back to James C. Maxwell in the 19th century. It was before the
Civil War that the "big error" you and Barry found started.

I guess it all comes down to if Barry and Yuri are right, or if nearly
every professor, scientist, and engineer from Maxwell to today are
correct. I can measure ANY antenna and prove things behave as I
described. Can you do the same?

73 Tom