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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Cecil Moore wrote in message ...
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

What example? I look at the page, and all I see is a current
distribution model for an antenna using stubs. ?? Where is the model
of the one using lumped inductance? I tried modeling a couple of
antennas myself using multiple 1/2 wave elements and inductance as
phasing coils just to test this out. But I used three elements instead
of four. I do not see any major change in current distribution when
compared to feeding all three with three separate sources. Minimum
current is at the ends of each section in both cases.
But I do see a bit less gain with the lumped inductance version, and
not quite as tight a pattern. This *might* be a point of error, but
I'd have to look more carefully into that. It's quite possible that
feeding with separate sources is superior in the real world, and it's
reflected in the model. But if this is an error in the model, I would
think that it only applies to arrays with lumped inductance used for
phasing coils. I very seriously doubt this error would apply to
modeling short coil loaded verticals. Or even large arrays that used
lumped inductance for loading, and not phasing purposes. Like I've
said, when I phase elements, I usually use separate sources to feed.
That way I can control the phase angle to whatever I want it to be.
MK

Mark Keith wrote:
Cecil Moore wrote in message ...

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

What example? I look at the page, and all I see is a current
distribution model for an antenna using stubs.

The example is four 1/2WL phased sections with "PHASE-REVERSING"
coils. The current is flowing into both ends of the coils at the
same time. Please show me an EZNEC model that allows current to
flow into both ends of the coil at the same time. You can model
that antenna using stubs but you cannot model that antenna using
lumped inductance. This is an example of an antenna that EZNEC
models with a "gross modeling error". With EZNEC, the current
never reverses phase as it must for that antenna to work properly.
--
73, Cecil http://www.qsl.net/w5dxp



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Mark Keith wrote:

Cecil Moore wrote:

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

What example? I look at the page, and all I see is a current
distribution model for an antenna using stubs. ?? Where is the model
of the one using lumped inductance?

Scroll on down. It's four 1/2WL array sections separated by a "phase
reversing coil".

I tried modeling a couple of
antennas myself using multiple 1/2 wave elements and inductance as
phasing coils just to test this out. But I used three elements instead
of four. I do not see any major change in current distribution when
compared to feeding all three with three separate sources.

Turn on the CI feature, display the current phase, and you will
see the difference. With EZNEC's lumped coils, the currents in the
outside sections are 180 degrees out of phase with what they need
to be.

But I do see a bit less gain with the lumped inductance version, and
not quite as tight a pattern. This *might* be a point of error, but
I'd have to look more carefully into that.

When you turn on the 'display current phase' feature, you will
see the difference. The currents in each 1/2WL sections are supposed
to be in phase. With EZNEC's lumped coils, they are out of phase no
matter what coil reactance is chosen. That's why there's more gain
using multiple sources. The errors are minimized using multiple sources.
--
73, Cecil, W5DXP

Cecil Moore wrote in message

Scroll on down. It's four 1/2WL array sections separated by a "phase
reversing coil".

I see a diagram, but no pattern plots or current distribution plots.
I'm curious to see how your's compared to mine. So far, after juggling
many different coil inputs, about the best gain I can get broadside is
3.54 dbi. "three 1/2 wave elements set end to end as a single wire
with the coils in the proper places on the wire ends" With separate
sources, I can get nearly 5 dbi. One note...End to end 1/2 waves is
not an optiumum spacing for max gain...

I tried modeling a couple of
antennas myself using multiple 1/2 wave elements and inductance as
phasing coils just to test this out. But I used three elements instead
of four. I do not see any major change in current distribution when
compared to feeding all three with three separate sources.

Turn on the CI feature, display the current phase, and you will
see the difference. With EZNEC's lumped coils, the currents in the
outside sections are 180 degrees out of phase with what they need
to be.

I wasn't using eznec...

But I do see a bit less gain with the lumped inductance version, and
not quite as tight a pattern. This *might* be a point of error, but
I'd have to look more carefully into that.

When you turn on the 'display current phase' feature, you will
see the difference.

Again, wasn't using eznec, but I looked in eznec for that feature and
couldn't find it. Is it in the demo version?
The currents in each 1/2WL sections are supposed
to be in phase. With EZNEC's lumped coils, they are out of phase no
matter what coil reactance is chosen.

Dunno, mine seem to be fairly well in phase. But not as good a
pattern or as much gain as using separate sources and elements. But
being as the overall current distribution seems little changed either
way, I'm not going to speculate on the reason at this point. With the
separate source antenna, I placed the elements as close together as
possible in order to be close to the loaded version in total length.

That's why there's more gain
using multiple sources. The errors are minimized using multiple sources.

This is quite possible. But I still don't think this would cause
noticable error when modeling short coil loaded antennas, or arrays
where the coil didn't act as a phasing device. Surely not a short
mobile whip. I doubt even with complex arrays if all the coils are for
loading purposes only. Sure, there may be some error, but not much
anyone can do about it, unless they design a new modeling engine. I
would think any error would be a db or less in most cases. Not really
worth worrying about. Or to me anyway...:/ When phasing elements, I
prefer separate sources anyway. And when designing mobile antennas, I
don't model them.
I calculate in terms of efficiency. The appx pattern and current
distribution is a given...
Seriously speaking...I think you can take Reg's vertload program, and
get as close as you would ever need to get as far as designing a
mobile whip, or short loaded vertical. It will tell you the best appx
place for the coil, the effects of wire dia, coil dia, coil length,
adding lower masts, adding upper stingers, ground loss, etc, etc,
about as well as you will ever need to use for designing such an
antenna. And if you feed it an accurate ground loss number, you know
your appx efficiency. After farting around with it a couple of years,
it seems to be pretty accurate comparing it to the real world. And
it's not even zipped up... MK

Mark Keith wrote:
I see a diagram, but no pattern plots or current distribution plots.
I'm curious to see how your's compared to mine. So far, after juggling
many different coil inputs, about the best gain I can get broadside is
3.54 dbi. "three 1/2 wave elements set end to end as a single wire
with the coils in the proper places on the wire ends" With separate
sources, I can get nearly 5 dbi. One note...End to end 1/2 waves is
not an optiumum spacing for max gain...

That difference in gain is because one cannot model a phase reversing
coil with a lumped inductive reactance. A workaround is needed and
yours is to use multiple sources. Mine is to use inductive stubs.

Again, wasn't using eznec, but I looked in eznec for that feature and
couldn't find it. Is it in the demo version?

I'm using DOS EZNEC 2.0 but I assume 3.0 has the same features. On
2.0 a Ctrl-I changes the current display from magnitude only to
magnitude and phase.

Dunno, mine seem to be fairly well in phase. But not as good a
pattern or as much gain as using separate sources and elements. But
being as the overall current distribution seems little changed either
way, I'm not going to speculate on the reason at this point.

That's the point. The current distribution is NOT the same either way.
I'm pretty sure you are displaying the current magnitude, not the
current phase. Given that the EZNEC lumped inductive reactance cannot
reverse the phase, the phases will always be 180 degrees apart in
adjacent 1/2WL sections and will not result in maximum gain or
minimum beamwidth.

This is quite possible. But I still don't think this would cause
noticable error when modeling short coil loaded antennas, or arrays
where the coil didn't act as a phasing device.

If I remember correctly, all you asked for was an example where EZNEC
didn't provide the correct results. Antennas using phasing coils is
that example. The lumped inductive reactance will not model a phasing
coil. It's not a big deal since there exist workarounds. I'm going to
try a parallel inductance and capacitance and see what happens to the
phase of the currents in EZNEC.
--
73, Cecil, W5DXP