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 Jan 3, 9:33*am, "Dale Parfitt" wrote:
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

Wrong.!
The primary current is still flowing at the center. Particles occupy
the surface of the inside
and with the inter rejection of like particles produce a hoop stress
between them which
cannot be broken by a eddy current field, if present Thus the
particles cannot be ejected even tho there
is the primary ,current flow in the center ofr the tube. Remember.
the presence of particles is cast in stone
via the extension of the Gaussian law of statics. The presumption that
the current is near zero
is false until proven otherwise.. There is absolutely NO evidence that
reflection occurs in any shape or form at the
material ends of a radiator and all that pertains to such. PERIOD
Art Unwin KB9MZ.........xg

"Art Unwin" wrote in message
...

Wrong.!

I told you so!

The primary current is still flowing at the center. Particles occupy
the surface of the inside
and with the inter rejection of like particles produce a hoop stress

'hoop stress' now there's a good term for particle interaction!

between them which
cannot be broken by a eddy current field, if present Thus the
particles cannot be ejected even tho there
is the primary ,current flow in the center ofr the tube. Remember.
the presence of particles is cast in stone

the stone in this case is art's brain.

via the extension of the Gaussian law of statics. The presumption that
the current is near zero
is false until proven otherwise.. There is absolutely NO evidence that
reflection occurs in any shape or form at the
material ends of a radiator and all that pertains to such. PERIOD

nah, just because i can measure it with my simple tdr here doesn't mean it
happens... its all the magical mystery levitating neutrinos that cause all
the fun.

On Jan 3, 10:37*am, Art Unwin wrote:
There is absolutely NO evidence that
reflection occurs in any shape or form at the
material ends of a radiator and all that pertains
to such. * *PERIOD.
____________

Art, the link below leads to empirical proof that such reflections
exist.

H. Gihring and G. Brown of RCA measured the relative current
distribution parallel to the axis of monopole radiators of several
lengths and widths, using an r-f current probe driving a thermal
meter.

The current distribution measured for the three radiator lengths
plotted all show the presence of reflections from the top of the
vertical wire, and in all three cases, current falls to zero at the
end of the radiator.

These are all fractional wavelength radiators not meeting your
definition of an antenna in "equilibrium."

This demonstrates that r-f current does not travel on the outside of a
wire on the way to the open end, and return from the open end along a
non-radiating path down the center of that conductor, as you believe.

http://i62.photobucket.com/albums/h8...reAntennas.gif

RF

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