Wes Stewart wrote:
I downloaded a couple of them, but I have a question. I opened them
using MultiNEC, which reads all of the popular modeling program file
formats. The loads did not import, but when I opened the same files
in EZNEC 3 I saw them as R+jX loads with only an 'X' value.

You can put in any R and XL value, Wes. The phase of the current will
not change. The magnitude decreases and the phase stays the same.

I learned from Dan, AC6LA, the author of MultiNEC, that some early
EZNEC versions save all loads as Laplace and he doesn't read those
into MultiNEC. Opening the files in EZNEC 3 and then just resaving
them makes the import into MultiNEC work okay, but this makes me
suspect that using your earlier files in my later version might be a
problem. The documentaion says otherwise though, but to be sure, what
are the actual load parameters.

Well, your Laplace files won't run on my EZNEC version 2.0. They all
come up as zeros. So I don't know what loads you used either.

I don't want to comment further until I know exactly what you are
using.

You can vary R and XL values from zero to infinity. The phase of the
current never changes. I tried values from 1+j300 to 1000+j300000
and it only affected the magnitude, not the phase.
--
73, Cecil http://www.qsl.net/w5dxp



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On Mon, 02 Feb 2004 22:28:55 -0600, Cecil Moore
wrote:

|Wes Stewart wrote:
| I downloaded a couple of them, but I have a question. I opened them
| using MultiNEC, which reads all of the popular modeling program file
| formats. The loads did not import, but when I opened the same files
| in EZNEC 3 I saw them as R+jX loads with only an 'X' value.
|
|You can put in any R and XL value, Wes. The phase of the current will
|not change. The magnitude decreases and the phase stays the same.

Okay, I guess that means the answer is: you used R+jX loads.
|
| I learned from Dan, AC6LA, the author of MultiNEC, that some early
| EZNEC versions save all loads as Laplace and he doesn't read those
| into MultiNEC. Opening the files in EZNEC 3 and then just resaving
| them makes the import into MultiNEC work okay, but this makes me
| suspect that using your earlier files in my later version might be a
| problem. The documentaion says otherwise though, but to be sure, what
| are the actual load parameters.
|
|Well, your Laplace files won't run on my EZNEC version 2.0. They all
|come up as zeros. So I don't know what loads you used either.

Mine aren't Laplace loads. There are straight RLC with C=0.

|
| I don't want to comment further until I know exactly what you are
| using.
|
|You can vary R and XL values from zero to infinity. The phase of the
|current never changes. I tried values from 1+j300 to 1000+j300000
|and it only affected the magnitude, not the phase.

It remains to be seen in my mind whether you are correct in your
assertions; however, I believe that you have stated that in your Kraus
reference that he used the self-resonance of the inductors to do the
magic.

How on Earth can you expect a load consisting of only R and Xl to be
self-resonant?

Wes Stewart wrote:
Mine aren't Laplace loads. There are straight RLC with C=0.

The 'LO' display says "Laplace Coefficients", "Select to show
values", and the values are all zero. The feedpoint impedance
of the antenna is infinite.

I believe that you have stated that in your Kraus
reference that he used the self-resonance of the inductors to do the
magic.

No magic - just relatively simple experiments. 1/2WL of a helical
antenna reverses the phase of the current just like a 1/2WL wire
does, over ground or in free space.

How on Earth can you expect a load consisting of only R and Xl to be
self-resonant?

I *don't* expect such a coil to simulate reality. That's the whole problem.
The artificial lumped load software doesn't match reality. It only
approaches reality for "physically small" coils. Once again, a 75m Texas
Bugcatcher coil is not physically small.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote in message

I *don't* expect such a coil to simulate reality. That's the whole problem.
The artificial lumped load software doesn't match reality. It only
approaches reality for "physically small" coils. Once again, a 75m Texas
Bugcatcher coil is not physically small.

It's physically small enough that any error should be small. IE: 1 db
or less.
This has been shown a few times. Myself, I don't lose much sleep over
the phasing coil dilemma. I don't think it will be much of an issue
when modeling simple short loaded whips. Being there is a workaround
for phasing antennas, IE: separate sources where you can define the
phase angle, the antenna can still be modeled.
There is something that keeps bothering me and my beady mind though...
You say the current going "one way" will be fairly constant across the
coil. Will the coil position effect this? If not, that creates a new
problem.
If the coil position does not effect the current taper going "one
way", I don't see how it would coming back the other way. Regardless
of coil position. If the current is constant going one way, seems to
me it would also be constant the other way. So in effect, they would
cancel each other out, and would still be fairly constant. I guess
what I want to see is experiments to test your theory of coil position
effecting the current taper. IE: You claim a center load would have
constant current, but off center would not. Seems to me, if this is
true, there should be a position that places maximum current at the
top of the coil, not bottom. If you never see this, I would be
suspect.
Well, back to my 1 db or less rubber room... MK

Mark Keith wrote:

Cecil Moore wrote in message

I *don't* expect such a coil to simulate reality. That's the whole problem.
The artificial lumped load software doesn't match reality. It only
approaches reality for "physically small" coils. Once again, a 75m Texas
Bugcatcher coil is not physically small.

It's physically small enough that any error should be small. IE: 1 db
or less.

A 13% error is small? The error is even larger than that for the current
at the top of the coil.

If the coil position does not effect the current taper going "one
way", I don't see how it would coming back the other way. Regardless
of coil position.

The forward current and reflected current phasors rotate in opposite
directions. Sometimes they are in phase and sometimes they are out
of phase. In a lossless transmission line, the forward current and
reflected current are absolutely constant with zero taper. Yet they
still result in standing waves with minimum and maximum points. This
is explained on my web page.

Seems to me, if this is
true, there should be a position that places maximum current at the
top of the coil, not bottom.

I have already said multiple times, depending upon where the coil is
placed, the net current into the coil can be less than, equal to, or greater
than the net current coming out. It all depends upon the phasor sum of the
forward current and reflected current. It can be zero or maximum or
anything in between depending upon where the coil is placed. For Kraus'
phase-reversing coil, the net current is zero at both ends and maximum
in the middle of the coil.
--
73, Cecil http://www.qsl.net/w5dxp/current.htm



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

Cecil Moore wrote in message

I *don't* expect such a coil to simulate reality. That's the whole problem.
The artificial lumped load software doesn't match reality. It only
approaches reality for "physically small" coils. Once again, a 75m Texas
Bugcatcher coil is not physically small.

It's physically small enough that any error should be small. IE: 1 db
or less.

A 13% error is small? The error is even larger than that for the current
at the top of the coil.

I don't know where this 13% comes from, but how many db difference
would it make in the modeling results? I bet it's about 1 or less. If
you have an 8 ft antenna, with a 1 ft tall coil, no matter what the
current taper is across the coil, it will not drastically effect the
modeling results. At least 3 or 4 people have shown this. The coil is
not a large enough portion of the overall antenna. And any taper of
the current along that one foot section is not going to make a
difference more than about 1 db. Usually less.



Seems to me, if this is
true, there should be a position that places maximum current at the
top of the coil, not bottom.

I have already said multiple times, depending upon where the coil is
placed, the net current into the coil can be less than, equal to, or greater
than the net current coming out. It all depends upon the phasor sum of the
forward current and reflected current. It can be zero or maximum or
anything in between depending upon where the coil is placed. For Kraus'
phase-reversing coil, the net current is zero at both ends and maximum
in the middle of the coil.

I know you have said it multiple times, but so far I don't recollect
anyone actually measuring a real world coil, and finding max current
at the top of the coil. That is what is bothering me. MK

Mark Keith wrote:
Cecil Moore wrote:
A 13% error is small? The error is even larger than that for the current
at the top of the coil.

I don't know where this 13% comes from, but how many db difference
would it make in the modeling results?

Uh Mark,
1 dB error = 13% error 10^(0.1) = 1.26
2 dB error = 29% error 10^(0.2) = 1.58
3 dB error = 50% error 10^(0.3) = 2.00

I know you have said it multiple times, but so far I don't recollect
anyone actually measuring a real world coil, and finding max current
at the top of the coil. That is what is bothering me. MK

Nobody builds an antenna that way but consider the following monopole.
Ground is at the left, top is at the right. Each of the following
1/4WL sections are electrical 1/4WL's.

1/4WL coil
Gnd-FP------1/4WL tubing------//////////------1/4WL stinger------

max--*-------------------------------*-------------------------
* * *
* * *
Current min-------------------*----------------------------------*

The current at the feedpoint will be high. The current at the bottom of
the coil will be low. The current at the top of the coil will be high.
The current at the tip of the antenna will be low.
--
73, Cecil http://www.qsl.net/w5dxp



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Mark wrote in reply to Cecil,
(snip)

I have already said multiple times, depending upon where the coil is
placed, the net current into the coil can be less than, equal to, or
greater
than the net current coming out. It all depends upon the phasor sum of the
forward current and reflected current. It can be zero or maximum or
anything in between depending upon where the coil is placed. For Kraus'
phase-reversing coil, the net current is zero at both ends and maximum
in the middle of the coil.

I know you have said it multiple times, but so far I don't recollect
anyone actually measuring a real world coil, and finding max current
at the top of the coil. That is what is bothering me. MK


Hi Mark,
Cecil doesn't actually have to measure anything, since he's already convinced
he's right because his arguments agree with the theory he made up in his head.
Yuri is supposed to measure loading coils using fish tank thermometers and
such. The real test will be when someone tries to make a new, improved
antenna based on the belief that the current taper on the loading coil
of a physically short antenna makes a tinker's damn worth of difference
in the far field radiation of said antenna.
73,
Tom Donaly, KA6RUH

Cecil Moore wrote:
I have already said multiple times, depending upon where the coil is
placed, the net current into the coil can be less than, equal to, or greater
than the net current coming out.

Which end of the coil is the input and which end is the output?

73, Jim AC6XG

Jim Kelley wrote:

Cecil Moore wrote:
I have already said multiple times, depending upon where the coil is
placed, the net current into the coil can be less than, equal to, or greater
than the net current coming out.

Which end of the coil is the input and which end is the output?

The DC model strikes again. For AC, current flows out of the coil
input just as often as it flows in and into the coil output just
as often as it flows out. :-)

But by convention the 'input' of the coil is the end closest to
the antenna feedpoint.
--
73, Cecil http://www.qsl.net/w5dxp



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