Art wrote:
"We can then use the absolute standard equation of E = I R."

For ac (RF) that`s not true. The formula is E=IZ, where Z includes
reactance and resistance in quadrature. I`m not piling on but some
readers may believe Art.

Best regards, Ricxhard Harrison, KB5WZI

The "Method of Moments" (MOM) makes no assumptions about
current distribution on a radiator; it computes the current distribution.
The radiated field is then calculated based on the current distribution.

Frank

Exactly correct. EZNEC (including demo) users can get a good
illustration of this by looking at the pattern from the example file
Cardioid.ez which consists of two identical elements with perfect
spacing and perfectly ratioed base currents. Notice that the front/back
ratio is about 35 dB (dropping to about 31 dB with more segments for
more accurate results), while it should be essentially infinite. The
small back lobe is caused by modification of the current distribution on
the two elements caused by mutual coupling -- although the base currents
are perfectly equal in magnitude and 90 degrees out of phase, the fields
from the two elements aren't, due to their having slightly different
current distributions. When I first saw this back lobe with perfectly
ratioed base currents, I searched through the program code looking for
what I was certain was a bug. I finally realized that the result was
correct and that the lobe was caused by the altered current distribution
which the program had correctly calculated. For more about this, see
http://eznec.com/Amateur/Articles/Current_Dist.pdf.

The assumption of sinusoidal current distribution is strictly true only
with straight, isolated conductors which are infinitely thin, although
it's a reasonably good assumption in many other cases. Mathematical
analyses of antennas done before computers were pretty much limited to
cases where sinusoidal distribution was assumed, because a more accurate
determination of current distribution was virtually impossible to
calculate. The ability to determine the actual current distribution is
one of the very important advantages of computer analysis.

Roy Lewallen, W7EL

On Dec 28, 3:32*pm, Roy Lewallen wrote:
The "Method of Moments" (MOM) makes no assumptions about
current distribution on a radiator; *it computes the current distribution.
The radiated field is then calculated based on the current distribution..

Frank

Exactly correct. EZNEC (including demo) users can get a good
illustration of this by looking at the pattern from the example file
Cardioid.ez which consists of two identical elements with perfect
spacing and perfectly ratioed base currents. Notice that the front/back
ratio is about 35 dB (dropping to about 31 dB with more segments for
more accurate results), while it should be essentially infinite. The
small back lobe is caused by modification of the current distribution on
the two elements caused by mutual coupling -- although the base currents
are perfectly equal in magnitude and 90 degrees out of phase, the fields
from the two elements aren't, due to their having slightly different
current distributions. When I first saw this back lobe with perfectly
ratioed base currents, I searched through the program code looking for
what I was certain was a bug. I finally realized that the result was
correct and that the lobe was caused by the altered current distribution
which the program had correctly calculated. For more about this, seehttp://eznec.com/Amateur/Articles/Current_Dist.pdf.

The assumption of sinusoidal current distribution is strictly true only
with straight, isolated conductors which are infinitely thin, although
it's a reasonably good assumption in many other cases. Mathematical
analyses of antennas done before computers were pretty much limited to
cases where sinusoidal distribution was assumed, because a more accurate
determination of current distribution was virtually impossible to
calculate. The ability to determine the actual current distribution is
one of the very important advantages of computer analysis.

Roy Lewallen, W7EL

If current distribution is calculated correctly as stated then the
answer with respect
to the route taken of the current of a fractional wave antenna should
be available and beyond doubt
as the program is derived from Maxwells laws. The distributed current
should be DC based if current flow is thru the center
of the radiator. As far as the resistance encountered on reverse flow
on the outside of a radiator the figure provided by computor programs
should be rather interesting as I have never encountered in print
suggested figures. In accordance with some engineers the radiation
resistance but be stated as the radiation impedance to avoid sniping
Art

"Roy Lewallen" wrote in message
. ..

The "Method of Moments" (MOM) makes no assumptions about
current distribution on a radiator; it computes the current
distribution.
The radiated field is then calculated based on the current distribution.

Frank

Exactly correct. EZNEC (including demo) users can get a good illustration
of this by looking at the pattern from the example file Cardioid.ez which
consists of two identical elements with perfect spacing and perfectly
ratioed base currents. Notice that the front/back ratio is about 35 dB
(dropping to about 31 dB with more segments for more accurate results),
while it should be essentially infinite. The small back lobe is caused by
modification of the current distribution on the two elements caused by
mutual coupling -- although the base currents are perfectly equal in
magnitude and 90 degrees out of phase, the fields from the two elements
aren't, due to their having slightly different current distributions. When
I first saw this back lobe with perfectly ratioed base currents, I
searched through the program code looking for what I was certain was a
bug. I finally realized that the result was correct and that the lobe was
caused by the altered current distribution which the program had correctly
calculated. For more about this, see
http://eznec.com/Amateur/Articles/Current_Dist.pdf.

The assumption of sinusoidal current distribution is strictly true only
with straight, isolated conductors which are infinitely thin, although
it's a reasonably good assumption in many other cases. Mathematical
analyses of antennas done before computers were pretty much limited to
cases where sinusoidal distribution was assumed, because a more accurate
determination of current distribution was virtually impossible to
calculate. The ability to determine the actual current distribution is one
of the very important advantages of computer analysis.

Roy Lewallen, W7EL

Thanks for the info. A very interesting link. I have experimented
with NEC models of phased arrays, and found the same problem
with a small back lobe. I followed the procedure in the ARRL
Antenna book, which involved calculating the elements in a 2 X 2
complex Z matrix, for a 2 element phased dipole array. The
results appeared to be very good, but I never actually built it.

Frank, VE6CB

In article , Roy
Lewallen wrote:


The assumption of sinusoidal current distribution is strictly true only
with straight, isolated conductors which are infinitely thin, although
it's a reasonably good assumption in many other cases. Mathematical
analyses of antennas done before computers were pretty much limited to
cases where sinusoidal distribution was assumed, because a more accurate
determination of current distribution was virtually impossible to
calculate. The ability to determine the actual current distribution is
one of the very important advantages of computer analysis.

Roy Lewallen, W7EL

Hello, Roy, and while the above is certainly correct, you're probably
wasting your time. Many folks like to fashion their own "reasonable"
explanations even when they're completely off track (should I mention the
CFA again?). Of course they're always right and it's the rest of the
world who's wrong. Certain folks on this ng appear to be in constant need
of validation. Persons without some knowledge of the underlying physics
and applied math are destined to reach the wrong conclusions IMO. Of
course that's not going to stop some from building a CFA because as we all
know it's the standard comms antenna used at the Groom Lake facility to
keep in touch with Klaatu. Sincerely, and 73s from N4GGO,

John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337

J. B. Wood wrote:

Hello, Roy, and while the above is certainly correct, you're probably
wasting your time. Many folks like to fashion their own "reasonable"
explanations even when they're completely off track (should I mention the
CFA again?). Of course they're always right and it's the rest of the
world who's wrong. Certain folks on this ng appear to be in constant need
of validation. Persons without some knowledge of the underlying physics
and applied math are destined to reach the wrong conclusions IMO. Of
course that's not going to stop some from building a CFA because as we all
know it's the standard comms antenna used at the Groom Lake facility to
keep in touch with Klaatu. Sincerely, and 73s from N4GGO,

John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337

If what you say is true, I am wasting my time. But I believe there's a
more diverse group of readers:

1. The people who already already know and understand what I'm explaining;
2. The people who think they know and understand what I'm explaining,
but don't, and won't change their minds no matter what I write; and
3. The people who are willing to read and understand what I write, and
learn from it or at least think about it.

Just like medical triage, only one of the three groups can be helped, in
this case #3. It's for those folks that I take the time to post. I hear
from them in various ways from time to time, so I know they're out
there. And I'm glad to pass along to them what I've learned, when I can.

Roy Lewallen, W7EL

On Dec 29, 1:36*pm, Roy Lewallen wrote:
J. B. Wood wrote:

Hello, Roy, and while the above is certainly correct, you're probably
wasting your time. *Many folks like to fashion their own "reasonable"
explanations even when they're completely off track (should I mention the
CFA again?). *Of course they're always right and it's the rest of the
world who's wrong. *Certain folks on this ng appear to be in constant need
of validation. *Persons without some knowledge of the underlying physics
and applied math are destined to reach the wrong conclusions IMO. *Of
course that's not going to stop some from building a CFA because as we all
know it's the standard comms antenna used at the Groom Lake facility to
keep in touch with Klaatu. *Sincerely, and 73s from N4GGO,

John Wood (Code 5550) * * * *e-mail: * * * * * * * * * *
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337

If what you say is true, I am wasting my time. But I believe there's a
more diverse group of readers:

1. The people who already already know and understand what I'm explaining;
2. The people who think they know and understand what I'm explaining,
but don't, and won't change their minds no matter what I write; and
3. The people who are willing to read and understand what I write, and
learn from it or at least think about it.

Just like medical triage, only one of the three groups can be helped, in
this case #3. It's for those folks that I take the time to post. I hear
from them in various ways from time to time, so I know they're out
there. And I'm glad to pass along to them what I've learned, when I can.

Roy Lewallen, W7EL

Roy,
That is exactly how I felt when I declared that the addition of a
radiator
to a Gaussian statics field under the application of a time varying
field equates to the
mathematics of Maxwells laws. Nobody, including you, showed an error
in that thinking.
Another person provided the mathematics that proved my point again ,
nobody could disprove it.
Anybody can view the book by Ramo and co "Fields and waves in
communication Engineering"
where in Appendix 11 where the a sample method of tackling the proof
is available in it's entirety.
Some could even read the chapter on radiastrion which spells out
problems with the existing aproach.
Remember when the presence of particles on a radiator is determined by
any person well versed in mathematics
and science then the true vehicle of communication is thus determined.
All of the above is directly
applicable to the stance in words only that you have expressed above
but..........no action
It blows my mind when people desert from mathematics and science in
efforts to prevent change.
T,here is no evidence what so ever that Newton's laws applicable in
this case has now been discarded in science
and that evidence destroys the notion of communication and the
emmission of light can be attributed to a field wave form
instead of the particles outlined in Gaussian law.
Art

Roy Lewallen wrote:
1. The people who already already know and understand what I'm explaining;

Assumes that you are omniscient and others should worship at
your feet.

2. The people who think they know and understand what I'm explaining,
but don't, and won't change their minds no matter what I write;

Assumes that you are omniscient and anyone who disagrees with
you is wrong.

3. The people who are willing to read and understand what I write, and
learn from it or at least think about it.

Assumes that you are omniscient and people can only learn
facts from you.

Roy, I don't think that any assumption of your omniscience
is warranted. Is it impossible that you are wrong about
anything in the world? Is the reason that you absolutely
refuse to engage in a rational discussion of the role of
interference in antenna systems because you might be proven
to be wrong and also learn something new in the process?
--
73, Cecil http://www.w5dxp.com

On Mon, 29 Dec 2008 11:36:34 -0800, Roy Lewallen
wrote:

If what you say is true, I am wasting my time. But I believe there's a
more diverse group of readers:

1. The people who already already know and understand what I'm explaining;
2. The people who think they know and understand what I'm explaining,
but don't, and won't change their minds no matter what I write; and
3. The people who are willing to read and understand what I write, and
learn from it or at least think about it.

Just like medical triage, only one of the three groups can be helped, in
this case #3. It's for those folks that I take the time to post. I hear
from them in various ways from time to time, so I know they're out
there. And I'm glad to pass along to them what I've learned, when I can.

Roy Lewallen, W7EL

Well, this is probably a suitable time to offer my thanks for taking
the time to explain how things work (and to correct my screwups).
Thanks much. I suspect that the time and effort are not a major
problem. It's tolerating the nonsense that passes as a substitute for
intelligence that bothers me. It's difficult to argue with
unsubstantiated illogic and one-line simulated cleverness.

I do the same in alt.internet.wireless.
http://groups.google.com/groups/profile?hl=en&enc_user=bLQuYRAAAACBvdjA7WBXQw3w3fq wxHRj
Hmmm... there should be much more dating back to about 1987.

One of my tag lines is:
"I judge people by their willingness and ability to learn".
I have no problem with those that disagree with me. It's easy enough
to make the distinction between disagreement and learning failure. If
they understand both sides of a debate, they're doing just fine.
Otherwise, you're debating against dogma and bias, with little home of
having anyone change their opinion.

I'm mostly in #3. I read, learn, sometime ask, occasionally comment,
and save some postings for reference. I'm fairly well informed in my
areas of expertise, but am seriously lacking in others. Antennas is
one of those where I'm lacking. Sometimes you go over my head, which
is not a problem. I can dig out the details later. However, some
URL's, references, and additional reading pointers would be helpful.
Overall, your postings are all useful, interesting, and well worth
reading.

As for the diversity of the readers, it's probably all over the map.
You have the difficult problem of trying to write something that is
understandable by every knowledge level from complete beginner to
professional antenna designer. It's easy if you know something about
the person with whom your discussing some topic, but very different if
you're dealing with an anonymous visitor.

Thanks again.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Art Unwin" wrote
The antenna compendium states that an assumption
is made with MoM programs that an assumption is made that current
in a radiator is sinusoidal where as we all know that the current
degrades in aplitude dependent on radiator length.
_____________

Art, the current distribution along even the shortest (fractional
wavelength), constant OD radiator also is ~sinusoidal.

Currrent always is near zero at the open end of a linear radiator of every
physical length. The shape of the current wave formed along a very short
radiator appears to be very close to triangular. But in fact that
"triangular" current distribution is just a very short section of a
sinusoidal waveform.

N.B. that MoM programs show exactly this for radiators that are very short
in terms of electrical wavelengths. This also is proven mathematically in
the antenna engineering textbooks of Kraus, Balanis, Johnson & Jasik, etc
etc.

RF

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