On Fri, 26 Jun 2009 22:07:13 -0700 (PDT), dykesc
wrote:

What I am having trouble with is how to include a longwire
RF energy sink at the source end of my antenna model.

There are any number of alternatives, each matching the situation of
"someone." They vary by rather simple to rather elaborate estimations
of "ground." At least one can be found in the generous help manual.

The trick is how well you know your "ground's" characteristic to
sufficient accuracy. Chances are you (given you have an ad hoc
design) you barely know. This, of course, translates into a model of
equal imprecision.

Myself, I lay out several dozen radials over an average earth and
connect to it. If it is a simple dipole, I lay out a ground mat below
the antenna (it does make a difference).

73's
Richard Clark, KB7QHC