Owen Duffy wrote:
wrote in
oups.com:
On Jun 3, 9:45 pm, John Smith I wrote:
wrote:
... screwed in too.. I've never noticed any real RF coupling
problems with
a
metal mast. You will see that with metal that parallels the antenna
legs
...
Amazing we have not heard from the "EZNEC Experts" with plots of a
metal vs. non-metal support ...
JS
"John Smith" doesn't hear from this "EZNEC Expert" because I plonked him
a long time ago.
If the wires of the dipole are exactly perpendicular to the feedline,
and
no common mode currents, the plots should be the same.
The more sloping, the more coupling I would think, but even then,
it's rarely a problem.
Modelling the Inverted V without its support conductive mast is a little
like modelling it without a real model of its feedline, both ignore real
things that impact the antenna to some extent.
Owen
If you model the antenna as being perfectly symmetrical, then it makes
no difference whether you include the mast in the model or not -- the
result will be the same (assuming that the mast isn't in electrical
contact with the antenna). It might be interesting to purposefully make
the antenna model a bit non-symmetrical to see what effect the mast
would then have.
If you're not using an effective balun, adding a feedline to the model
will have an impact on the result (as it will on a real antenna) even if
the antenna is symmetrical, provided that you include the common mode
current path in the feedline model. This means modeling the feedline as
two wires, or by using the transmission line object plus a wire to
represent the outside of a coaxial cable. To be truly realistic, you
need to include the entire path to the Earth. This is seldom known, so
about the best you can do is to fiddle the length and orientation of
your feedline model to find the worst case and assume the real antenna
will have less common mode current than that.
Roy Lewallen, W7EL