On Jan 3, 9:33*am, "Frank" wrote:
wrote in message

...



I've been using 4Nec2, a freeware antenna modeling program based on
NEC-2 (Numerical Electromagnetic Code). I'm wondering if anyone could
provide some insight as to just how it models current at the ends of
wires that are not connected to anything (a.k.a. "free ends" or "open
ends").

Does NEC-2 model "end caps" at free ends, which is equivalent to
assuming wires are solid, or does it just set the current equal to
zero at the free ends, which is equivalent to assuming wires are
hollow? Is it possible that it does both, but the specific model is
determined by the choice of computational kernel (extended vs.
standard)?

I've tried looking through some of the NEC-2 documentation, but I
can't find a definitive answer.

-Dave, K3WQ

This is covered in:http://www.nec2.org/other/nec2prt1.pdf
pp 11 - 12.

Frank

Thanks, Frank, for shining some light into a dark corner. I
appreciate having that whole document now, too.

Cheers,
Tom

On Jan 3, 11:33*am, "Frank" wrote:
wrote in message

...



I've been using 4Nec2, a freeware antenna modeling program based on
NEC-2 (Numerical Electromagnetic Code). I'm wondering if anyone could
provide some insight as to just how it models current at the ends of
wires that are not connected to anything (a.k.a. "free ends" or "open
ends").

Does NEC-2 model "end caps" at free ends, which is equivalent to
assuming wires are solid, or does it just set the current equal to
zero at the free ends, which is equivalent to assuming wires are
hollow? Is it possible that it does both, but the specific model is
determined by the choice of computational kernel (extended vs.
standard)?

I've tried looking through some of the NEC-2 documentation, but I
can't find a definitive answer.

-Dave, K3WQ

This is covered in:http://www.nec2.org/other/nec2prt1.pdf
pp 11 - 12.

Frank

Frank
Please keep in mind the following
NEC is based totally on the extremely thin wire where various
assumption can be made
such as equations being equal to zero in the limit., These same
assumptions can not be held to
when dealing with thick radiators despite the closeness of the
approximations.
Best regards
Art

On Jan 3, 12:25*pm, Art Unwin wrote:
On Jan 3, 11:33*am, "Frank" wrote:



wrote in message

....

I've been using 4Nec2, a freeware antenna modeling program based on
NEC-2 (Numerical Electromagnetic Code). I'm wondering if anyone could
provide some insight as to just how it models current at the ends of
wires that are not connected to anything (a.k.a. "free ends" or "open
ends").

Does NEC-2 model "end caps" at free ends, which is equivalent to
assuming wires are solid, or does it just set the current equal to
zero at the free ends, which is equivalent to assuming wires are
hollow? Is it possible that it does both, but the specific model is
determined by the choice of computational kernel (extended vs.
standard)?

I've tried looking through some of the NEC-2 documentation, but I
can't find a definitive answer.

-Dave, K3WQ

This is covered in:http://www.nec2.org/other/nec2prt1.pdf
pp 11 - 12.

Frank

Frank
Please keep in mind the following
NEC is based totally on the *extremely thin wire where various
assumption can be made
such as equations being equal to zero in the limit., These same
assumptions can not be held to
when dealing with thick radiators despite the closeness of the
approximations.
Best regards
Art

Calculus is based on homogenous materials or planes where you can
refer dy/dx to
some thing aproaching zero. In the case of using this aproach where
the antenna diameter aproaches zero
this is an invalid aproach for accuracy but O.K. for aproximations. So
much for the foibles of theoretical mathematics.
The vanishing thin radiator cannot be applied directly to a non
homogenous material because at the limits of the the diameter
is unable to support the presence of eddy currents(skin depth) . In
other words the assumption of limi tess ness cannot be held if the
presence of
skin effect is true. Ofcourse if skin effect is not present then you
have a DC current where only copper losses are present.
As always with mathematics assumptions and preconditions are alway
subject to examination. This in no way takes away from the advantages
oif the NEC programs.
Art

Frank
Please keep in mind the following
NEC is based totally on the extremely thin wire where various
assumption can be made
such as equations being equal to zero in the limit., These same
assumptions can not be held to
when dealing with thick radiators despite the closeness of the
approximations.
Best regards
Art

The reference at http://www.nec2.org/other/nec2prt1.pdf p 21 deals
with the accuracey of NEC 2 in respect to the "Thin wire approximation".
From the NEC-4, theory manual, p 21, para 4: ".... the NEC-4 wire model
employes the extended boundary condition in the thin wire approximation,
so that the current is treated as a tubular distribution on the wire
surface......."

Calculus is based on homogenous materials or planes where you can
refer dy/dx to
some thing aproaching zero. In the case of using this aproach where
the antenna diameter aproaches zero
this is an invalid aproach for accuracy but O.K. for aproximations. So
much for the foibles of theoretical mathematics.

Your comments about calculus are confusing. A derivative
is always non-zero -- unless you are differentiating a constant.
The homogeneity, or otherwise, of a material is irrelevant
to the process of differentiation.

The vanishing thin radiator cannot be applied directly to a non
homogenous material because at the limits of the the diameter
is unable to support the presence of eddy currents(skin depth) . In
other words the assumption of limi tess ness cannot be held if the
presence of skin effect is true.

Most conductors are homogeneous. In fact I cannot think of
a non-homogeneous conductor. Even in plated conductors
the current flows in the plating.

Of course if skin effect is not present then you
have a DC current where only copper losses are present.
As always with mathematics assumptions and preconditions are alway
subject to examination. This in no way takes away from the advantages
oif the NEC programs.
Art

Copper loss still exists for high frequency currents.

73, Frank

On Jan 3, 2:44*pm, "Frank" wrote:
Frank
Please keep in mind the following
NEC is based totally on the extremely thin wire where various
assumption can be made
such as equations being equal to zero in the limit., These same
assumptions can not be held to
when dealing with thick radiators despite the closeness of the
approximations.
Best regards
Art

The reference athttp://www.nec2.org/other/nec2prt1.pdf*p 21 deals
with the accuracey of NEC 2 in respect to the "Thin wire approximation".
From the NEC-4, theory manual, p 21, para 4: ".... the NEC-4 wire model
employes the extended boundary condition in the thin wire approximation,
so that the current is treated as a tubular distribution on the wire
surface......."

Calculus is based on homogenous materials or planes where you can
refer dy/dx to
some thing aproaching zero. In the case of using this aproach where
the antenna diameter aproaches zero
this is an invalid aproach for accuracy but O.K. for aproximations. So
much for the foibles of theoretical mathematics.

Your comments about calculus are confusing. *A derivative
is always non-zero -- unless you are differentiating a constant.
The homogeneity, or otherwise, of a material is irrelevant
to the process of differentiation.
That is exactly my point. The skin is not hogenoius even if you
consider the resistive action to be constant in depth thus you cannot
put a limit on the thicknes
or diameter of the radiator! If you do put a limit anyway on skin
depth then you cannot apply the reasoning to a hollow tube.
We can talk back and forwards for ever on the analogy provided with
vanishingly thin radiators but until we break apart the mathematics
such that there is a reflection at the end of a radiator the posters
question cannot be answered.
If one is to model the situation as Cecil suggests we must first
determine how and where the reflection is created and the
applied math provided to support it. I can see no reference via
mathematics that shows the reversal or reflection of current flow
prior to the end of a cycle.If there were such an instance then there
must be a determination of the resistance radiation or otherwise
so that any assumption made is factual.




The vanishing thin radiator cannot be applied directly to a non
homogenous material because at the limits of the *the diameter
is unable to support the presence of eddy currents(skin depth) . In
other words the assumption of limi tess ness cannot be held if the
presence of skin effect is true.

Most conductors are homogeneous. *In fact I cannot think of
a non-homogeneous conductor. *Even in plated conductors
the current flows in the plating.

No that is not true as homogenous implies equilibrium and for skin
depth the value (e) comes into beingor what so0me would refer to as
decay

Of course if skin effect is not present then you
have a DC current where only copper losses are present.
As always with mathematics assumptions and preconditions are alway
subject to examination. This in no way takes away from the advantages
oif the NEC programs.
Art

Copper loss still exists for high frequency currents.

Very true Frank but the radiation resistance plus the resistance
encoutered by surface flow is not related/
proportional to the pure copper losses where skin resistance is not
present where in the absence of
skin depth leaves one with DC pulses.

I am ofcourse still interested what the NEC programs show for
reflection and consequental resistance
which I believe was in Cecil's thoughts to determine the truth.
Hopefully the dialogue between you and I will not drop to the level of
David's where he contendes that Gaussian law of STATICS
is one of the basic laws that Maxwell applied/used without the
required proof..On top of which he denies the applicability of statics
with electro magnetics thus any mathematical aproach cannot be
applicable which is absolutely crazy
The thrust of this thread is solely on the difference of radiation
with respect to hollow radiators and solid radiators and it should be
kept at that to provide a reasonable answer as required in any formal
debate.

73, *Frank

On Jan 2, 6:31*pm, wrote:
I've been using 4Nec2, a freeware antenna modeling program based on
NEC-2 (Numerical Electromagnetic Code). I'm wondering if anyone could
provide some insight as to just how it models current at the ends of
wires that are not connected to anything (a.k.a. "free ends" or "open
ends").

Does NEC-2 model "end caps" at free ends, which is equivalent to
assuming wires are solid, or does it just set the current equal to
zero at the free ends, which is equivalent to assuming wires are
hollow? Is it possible that it does both, but the specific model is
determined by the choice of computational kernel (extended vs.
standard)?

I've tried looking through some of the NEC-2 documentation, but I
can't find a definitive answer.

-Dave, K3WQ

David
I see no reference with respect to the ratio between diameters so It
must reflect
solid conductors. If the elements were hollow there could be current
flow within the tube together with skin depth. However, the
communication must be consistent with straight line projectory and
thus the center of the tube would act like a Faraday cage. This is
different to current flow in the center of a solid radiator since
there can be no eddy current within a material of a RF radiator.
Remember, no matter how you read the NEC files equations arrived at
are often approximations since many time portions of equations are
assumed to be negligeable compared to the overall scheme of things and
thus deleted. Do that a few times and it is not known whether the
solutions is a greater or smaller approximation , only a closer
approximation that that created by a planar design. As a U.S.Senator
from Illinois once stated, a dollar here and a millions there and
pretty soon we are talking about real money (Sen Dirksen of Peoria)
Regards
Art

On Fri, 2 Jan 2009 16:31:08 -0800 (PST), wrote:

Does NEC-2 model "end caps" at free ends, which is equivalent to
assuming wires are solid, or does it just set the current equal to
zero at the free ends, which is equivalent to assuming wires are
hollow? Is it possible that it does both, but the specific model is
determined by the choice of computational kernel (extended vs.
standard)?

This presumes you are seeking a wire that has no current anywhere in
its interior. Clearly there is no such conductor as any conduction
via electrons (or the charge carrier of holes) must circulate about an
atom's nucleus which necessarily imposes an interior current for half
the orbit. The only exemption would be unless the conductor is one
atom thick where there would be no interior. This would then become a
quantum wire which would have problems of its own (called a coulomb
blockade). As such a topic is clearly beyond the scope of discussion
here, for all practical purposes wire is considered to be a bulk, even
for NEC-n and the notion of "end caps" is an artifact of other,
external considerations.

I've tried looking through some of the NEC-2 documentation, but I
can't find a definitive answer.

NEC-n designers are not interested in anticipating the questions to a
vast multitude of speculative scenarios exploring the edges of QED.
For instance, modern economics doesn't provide a definitive answer to
this question either (economists don't really find those same issues
germane either).

* * * * * * * * *

However, this question can be put to any NEC-n modeling package, and
an answer provided quickly with some effort - if you are a skilled
modeler. Further, the same question AND its NEC-n modeled answer can
be weighed at the bench for validity.

At the risk of introducing a practical example that can be tested at
the bench (knowing full well how that can tax the practical skills of
many arm-chair theorists), let's proceed with a simple experiment.

First, we approach the situation with a radiator that is both hollow
AND solid. Yes, a contradiction on the face of it, but explanation
will serve. A coax that is terminated at both ends with female BNC
connections has those ends capped with male shorting plugs. The net
effect is that the "conductor" has two paths, one that is the exterior
shield, and one that is the interior conductor. The shield and
conductor are shorted together at both ends. With such a connection,
we necessarily have a solid.

We drive the exterior shield with a direct connection. Let's simply
make it the vertical radiator against a field of radial ground wires.
To all intents and purposes, the coax is a slightly thickish radiator.
We can physically measure the current excitation along the length of
the exterior path quite simply. When we take the numbers and compare
it to the NEC-n model for a vertical radiator of equal thickness
against a field of radial wires, we find a very close agreement in
results.

NEC-n has been validated in the field.

If we break one of the male shorting caps open to insert a current
meter (replacing the shorting cap with the meter inside the coax);
then we discover there is no practical current inside the coax along
the inner conductor. This should be no mystery as it is a classic
expectation of Freshman physical science. {I will note here for the
purists that I have explicitly stated no "practical" current. There
is no one in this group who could possibly measure the impractical
current.}

To create the NEC-n model would require constructing a cage of wires
to simulate the shield, implanting an interior conductor to simulate
the inner conductor and shorting both ends. This is not a
intellectual leap, merely an hour's worth of careful design. I will
leave it to someone ELSE who cares about the issue to report the
current distribution of that interior wire. A very similar example is
already available at:
http://home.comcast.net/~kb7qhc/ante.../Cage/cage.htm
so complaints of the lack of resources, time, effort, understanding,
and the rest are hollow.

Barring reports to the contrary (and speculation counts for naught),
NEC-n remains validated in the field. I would like to see that
failure demonstrated, but untutored Arthru wholly lacks the skill in
the matter, so I won't hold my breath for his demonstration.

Then the only step that remains is to open the interior wire (in
either/both the physical real model and/or the model) and take new
current distribution numbers. This fully qualifies as an hollow
conductor (you can even remove the interior wire entirely to fully
qualify to the question).

The question is solved through the model without need for browsing
documentation.

If this doesn't serve, then the question wasn't all that important as
an issue in the first place. If this is a serious question, then it
is a necessary test. Barring reports of enumerated results, it then
the question becomes yet another troll. I would note this same test
fully quashes Arthru's speculations of interior currents of a
radiator.

No appeals to Gauss, Newton, Maxwell, or Einstein were necessary in
the production of this posting as results are self evident to the
skilled and naming those dead white scientists are employed only by
hucksters trying to validate patents (aka ego certificates).

73's
Richard Clark, KB7QHC