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

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

the only one who would care about that is art who believes that current
flows back down the inside of the conductor. for the rest of us an end of a
wire is an end of a wire... the difference in capacitance from a filled end
to a hollow tube, unless the diameter of the hollow tube is a good fraction
of a wavelength should be negligible.

Dave wrote:
the only one who would care about that is art who believes that current
flows back down the inside of the conductor. for the rest of us an end of a
wire is an end of a wire... the difference in capacitance from a filled end
to a hollow tube, unless the diameter of the hollow tube is a good fraction
of a wavelength should be negligible.

Has anyone ever measured a difference between aluminum
tubing and a solid aluminum rod at the end of an antenna?
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Dave wrote:
the only one who would care about that is art who believes that
current flows back down the inside of the conductor. for the rest of
us an end of a wire is an end of a wire... the difference in
capacitance from a filled end to a hollow tube, unless the diameter of
the hollow tube is a good fraction of a wavelength should be negligible.

Has anyone ever measured a difference between aluminum
tubing and a solid aluminum rod at the end of an antenna?

The rod is heavier.

On Jan 3, 9:49*am, Dave wrote:
Cecil Moore wrote:

Has anyone ever measured a difference between aluminum
tubing and a solid aluminum rod at the end of an antenna?

The rod is heavier.

Yes, yes, the rod is heavier. Very funny, but could someone answer
the original question.

-Dave, K3WQ

wrote in message
...
On Jan 3, 9:49 am, Dave wrote:
Cecil Moore wrote:

Has anyone ever measured a difference between aluminum
tubing and a solid aluminum rod at the end of an antenna?

The rod is heavier.

Yes, yes, the rod is heavier. Very funny, but could someone answer
the original question.

-Dave, K3WQ

The current is close to zero- why would it make any difference?
W4OP

On Sat, 03 Jan 2009 08:31:30 -0600, Cecil Moore
wrote:

Has anyone ever measured a difference between aluminum
tubing and a solid aluminum rod at the end of an antenna?

Maybe Horace Lamb or Oliver Heaviside? Skin effect is dependent on
frequency as well as the material, right? Is the thickness of the
aluminum tubing significant at the frequency where you plan to use it?

I missed the beginning of the thread, so what is the original question
pertaining to?

In any case, I believe the rod would be heavier. ; )

S.T.W.

Cecil Moore wrote:
"Has anyone ever measured a difference between aluminum tubing and a
solid rod at the end of an antenna?"

Unnecessary as the inside diameter of the tubing would have to be at
least 1/2-wavelength to admit significant RF energy.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Cecil Moore wrote:
"Has anyone ever measured a difference between aluminum tubing and a
solid rod at the end of an antenna?"

Unnecessary as the inside diameter of the tubing would have to be at
least 1/2-wavelength to admit significant RF energy.

Richard, it was a rhetorical question.
--
73, Cecil http://www.w5dxp.com

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