On Thu, 04 Dec 2003 14:55:51 -0600, Cecil Moore
wrote:

Richard Clark wrote:
Six, the differences of Models employing the protocol and those not
employing it shows about 0.5dB difference.

If you would like to see more difference, try to model a 180 degree
phase-shifting coil using EZNEC.

Not worth the effort.

Richard Clark wrote:

On Thu, 4 Dec 2003 11:08:21 -0600 (CST),
(Richard Harrison) wrote:
Yuri Blanarovich posted ON4UN`s Fig 9-22 from "Low-Band DXing".
45-degrees of the 90-degree total length of a center-loaded whip comes
from the loading coil. Current tapers cosinusoidally from 1A at the
drivepoint to 0A at the tip.

Hi Richard,

First, and unfortunately, the antenna offered was never anywhere close
to 45° tall. The one Yuri posted barely stood 20° tall.

Second, Yuri's complaint centered on the notion of Modeling, not
measuring. He was making a plea to improve the accuracy and
efficiency of Modelers (all of this is EZNEC implicit, or by extension
NEC generically). Yuri never demonstrated the so-called cosinusoidal
variation in either Models or in Measurement. In fact, Yuri never
demonstrated ANY variation in current along ANY radiator.


Third, the argument of lumped or distributed circuit properties had
been answered with a protocol BEFORE the argument started. The
protocol offered every bit of correlation to ON4UN's drawings.

Fourth, this correlation did not demonstrate a slavish equality to the
so-called cosinusoidal variation, but rather demonstrated a conceptual
agreement. In fact, the Model data shows a divergence from that
curve.

Fifth, no one has bothered to demonstrate anywhere, that with the
protocol, that it is or is not born out in measurement.

Six, the differences of Models employing the protocol and those not
employing it shows about 0.5dB difference. This responds to the
original complaint of Yuri, in that no remarkable efficiencies are
gained or lost by this debate. To make matters worse, no Measure of
differences has been made to accept or dismiss this Model either.
This of course returns us to methods and accuracies, and given the
forecast of 0.5dB, the prospects of that turning into a metaphysical
freak show are more prominent than field tests resolving it in the
noise.

73's
Richard Clark, KB7QHC

Bravo. Pretty much sums it all up in a nutshell. No one has shown an
example of gross modeling error to date. No examples, no beef is served.
MK
--
http://web.wt.net/~nm5k

Mark Keith wrote:
Bravo. Pretty much sums it all up in a nutshell. No one has shown an
example of gross modeling error to date.

What is the matter with the one I posted last week with phase-
reversing coils as described by Kraus on page 824 of _Antennas_
for-all_Applications_, third edition? If you missed it, look at

http://www.qsl.net/w5dxp/current.htm
--
73, Cecil http://www.qsl.net/w5dxp



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KB7QHC writes:

Yuri's complaint centered on the notion of Modeling, not
measuring.

No, the first problem was that I argued that current across the loading coil is
different, while W8JI still argues that it is equal, the rest developed from
that. I knew it was different, W9UCW measured it, other "calculated" and
"Kirchoffed" that it isn't.
I will get to measurements, just let me get my life back to normal and have
some time to do the decent job. In the mean time let the games continue :-)

Yuri

Jim, AC6XG wrote:
"But there`s no question that it`s possible to build an airplane that
flies, without understanding why it flies."

True, but it`s often better to understand what you are doing, especially
when innovating. Sometimes mistakes can be avoided. The Wright Brothers
certainly understood aerodynamics and worked hard to develop their
design before it ever flew.

They built the world`s first wind tunnel to perfect their airfoils while
trying to avoid possible fatal cut and trys. Because they knew why it
flew, The Wrights were the first to sustain powered flights.

Heath`s kits were airplanes before they started producing electronic
kits.

Best regards, Richard Harrison, KB5WZI

Art, KB9MZ wrote:
"What do you mean by that Richard?"

The Wrights were the first to sustain powered flight. That means the
first practical airplane.

It wasn`t really Ernest and Julio Gallo that first got Americans to fly.
It was the Wright Brothers. The Wrights were already accomplished
mechanical designers and bicycle manufacturers. They collected and
studied all the information on flight they could get from around the
world and analyzed it for flaws to avoid in their own work. They
designed a new aluminum engine from the ground up to avoid overloading
their new flying machine. These guys were serious and practical
scientists and engineers.

This all happened 100 years ago. After the prototype flew, the Wrights
went into production on air frames and engines. Many WW-2 aircraft were
powered by "Wright Cyclone Engines".

One of the original Wright engines was owned by a California collector.
When a replica of the original Wright Flyer was recently built from the
original plans and specifications, the nearly 100 year old engine was
obtained from the collector, bolted into the new-old airframe and the
engine worked very well in powered flight of the replica. The builders
of the replica tested it on the ground for thrust the same as the Wright
brothers had. When the plane flew it was just like old times.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:

Jim, AC6XG wrote:
"But there`s no question that it`s possible to build an airplane that
flies, without understanding why it flies."

True, but it`s often better to understand what you are doing, especially
when innovating.

It's probably true for antennas as well as airplanes.

73, Jim AC6XG

Cecil Moore wrote in message ...
Jack Smith wrote:
My understanding of the particular question being debated is that the
loading coil is physically small and at the frequency in question may
be safely treated as a lumped element, and that some have said that
current-in current-out.

A 200 cubic inch 75m bugcatcher coil is NOT physically small and should
NOT be treated as a lumped element if one desires real-world results.

Cecil
When I first started working on my antenna design I didn't look at a
coil
as representing degrees per se. What I did was to ascertain the
resonant
frequency and the Q of the coil and transpose this into a length
that resonated with the same Q at the original frequency. True, the
radiation per unit length is different and has to be accounted for (a
critical important factor when comparing toroids to air wound coils)
but this aproach is quite different from using the "degrees" aproach
which is not the same because of the radiation difference ( See Roy's
aproach).
This aproach was the one I took with my antenna design
and it worked very well in practice as well as being confirmed by a
"theoretical" computor programs.
This aproach then allows a tranditional aproach of viewing current
behavior as it moves thru a distributed resistance and its limited
radiation.
Is there a fallacy in this aproach ?
Appreciate any insights that you have on the above to further my
education
Best Regards
Art

Art Unwin KB9MZ wrote:
Is there a fallacy in this aproach ?

The 'gotcha' in such an approach is why distributed network analysis
had to be invented. The problem is ascertaining whether the model one
is using is sufficient for the task. One can be using the wrong model
and not realize it. It appears that is the problem that W8JI has
encountered with his insistence that net current through a coil is
always constant. If there are two constant currents flowing through a
real-world coil in opposite directions, the superposed net current
will not be constant.

Any time there exist forward waves and reflected waves, a lumped circuit
analysis would be suspect. Sometimes one gets the same results as a
distributed network analysis and sometimes not. What I do is keep the
distributed network analysis as a concept in the background to verify
the validity of any lumped circuit analysis.
--
73, Cecil http://www.qsl.net/w5dxp



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