Jack Twilley:
Sure, I could drop a line down to ground, but the antenna itself
doesn't work that way. It goes down a long coaxial line to the
transmitter, at which point the shield is grounded and the center
conductor is connected to the signal. Does that matter?

ASCII art fails me, Jack. You can model the coax
as a wire to ground, but that wire has to have all
the geometric twists and turns that your actual
coax takes getting to the transmitter. The coax
shield is part of your antenna system; it radiates
along with both sides of the dipole. And even at
your transmitter, "ground" isn't really ground.
There is a connecting wire between the transmitter
case and "earth" ground.

In reality, there is no such thing as "ground" with
RF.

The reason your post caught my eye is that I have
the same antenna system you do - coax-fed dipole
with no balun - and had to model my coax line
shield to get "real" EZNEC results.

Jim, K7JEB