David wrote:
Thanks for the model, I'll try it.

What is the diameter of the elements. I understand you can also vary the
feedpoint impedance by changing element diameter ? (Zo = 276 log(2S/d)

Open the EZNEC file. In the main window, click the Wires line to open
the Wires Window. Find the Diameter column, where you'll see the
diameter of each conductor.

The equation you give is approximately the characteristic impedance of a
transmission line, not the feedpoint impedance of a J-pole. The
relationship between the two is very tenuous and complex.

Roy Lewallen, W7EL