I don't know of any program better than EZNEC for this. (Most others are
just as capable.) You have to realize that the feedline is an integral
part of the antenna, so it must of course be part of the model. Because
it radiates, you have can't use the program's transmission line models,
but have to include the feedline as wires. Depending on the length and
orientation of the feedline, there might also be significant current
flowing from the rig to the Earth via whatever path it can take, and
this is also part of the antenna and must be included in the model if
the model is going to predict the antenna performance.

Just becuase we call one part of the radiating system an "antenna",
another a "feedline" and another "ground" doesn't give them magical
properties and prevent them from radiating. All can be part of the
radiating antenna system and, in the case of a Zepp, generally are.

Roy Lewallen, W7EL

Al Lorona wrote:
P.S. I should probably start a different thread to make this comment, but I
am still trying to find a good analysis program to enable simulation of an
balanced-line end-fed antenna, sometimes called a Zepp. This evidently is
one tough problem to solve.