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