I'm not sure where in this convoluted thread to put this, and please
excuse me if the point has been made before but I just wanted to
reiterate...

When you put up an antenna system, pretty much _everything_ in the
vicinity of the wires you think of as the "antenna" is actually part of
the antenna system. Of special concern are all conductors, as well as
big pieces of dielectric material and lossy material. Certainly ground
has a profound effect on the radiation pattern, for example.

I'm really not so concerned with "how much power is radiated from my
feedline" as I am with "what is the radiation pattern (and in some
cases, efficiency) of my entire antenna system." To the end of
controlling the radiation pattern, I may wish to suppress antenna
currents on things like support wires and feedlines. Or, I may model
the system and find that antenna currents on the feedline are really
not a problem. In the case where I do care, I can add "current baluns"
or "choke baluns" or other structures as needed, or change the
configuration to break up the unwanted currents. In some cases, a
balun can be as simple as a hunk of ferrite clamped over the feedline.
I've also used self-resonant coils of coaxial feedline to very
effectively suppress current at a particular frequency. Breaking up
support wires with insulators can be very useful.

If you think that antenna current on the feedline is always a BAD
thing, consider the coaxial collinear, where the sections of feedline
that compose the antenna are INTENDED to radiate. On the other hand,
with that antenna, it's very important to suppress antenna current on
the line feeding the antenna part, because it doesn't take much antenna
current on that line to mess up the radiation pattern. But with an 80
meter coax-fed dipole, the pattern may actually be better for some
purposes if you don't suppress the antenna current on the feedline.

Again, the question I care about is, "What is the pattern for this
antenna," not "How much power does the feedline radiate." Is this
really so different from caring more about properly loading a
transmitter and getting power efficiently to the antenna, instead of
caring specifically about transmission line SWR? Focus on what gets
you the results you want, not on red herrings or old husband's tales.

Cheers,
Tom

K7ITM wrote:
Again, the question I care about is, "What is the pattern for this
antenna," not "How much power does the feedline radiate."

The present question has nothing to do with reality. The
present question is: what is wrong with the simulation software?
--
73, Cecil http://www.qsl.net/w5dxp


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