Thread: Dish reflector
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Old April 23rd 09, 11:39 PM posted to rec.radio.amateur.antenna
Cecil Moore[_2_] Cecil Moore[_2_] is offline
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First recorded activity by RadioBanter: Mar 2007
Posts: 3,521
Default Loading coils: was Dish reflector

Roy Lewallen wrote:
I did and do support lumped element analysis for a very small toroidal
loading inductor, and extensively posted the reasons why in this
newsgroup about six years ago ("Current in antenna coils controversy",
2003). Cecil and Yuri were arguing that the coil would replace some
number of "degrees of antenna" and its current therefore would have a
substantial phase difference between input and output ends. I made and
posted careful measurements to support my statement, after which Cecil
invented his "standing wave current" and went off in various directions.


I didn't invent "standing wave current". Standing wave
current is what EZNEC displays for standing wave antennas.
Standing wave current is what Kraus describes graphically
on page 464, Figure 14-2, of "Antennas ...", 3rd edition.
Standing wave current is what Ramo and Whinnery describe
mathematically in "Fields and Waves ...".

It has been at least 5 years since I explained why
the phase of the current on a standing wave antenna cannot
be used to determine the delay in a wire or in a coil.
EZNEC, Kraus, Balanis, and Ramo and Whinnery all agree
with me and disagree with you. I explained, 5 years ago,
how the magnitude of the current can be used to calculate
the delay through a coil. All my explanations fell on
deaf ears and you called them gobblygook, or some such.

Once again, most of the current in a standing wave antenna
is of the form,

I = Imax*cos(kx)*cos(wt)

For any given time = t1, the phase of the current all up
and down the antenna does not change with x. The phase
is the same at the feedpoint, at the bottom of the coil,
at the top of the coil, and at the top of the stinger.
The phase of that current cannot be used to calculate
delay in a wire or through a coil.

You once said you were quick to admit a mistake. It has
been 5+ years since you made that conceptual mistake
and you have not admitted it yet.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com