Roy,

The model I used for the open stub J-pole was not the same as your 3
element col.

I used a vertical long element and vertical short element. They were
joined by a horizontal element at the base. The source was set at 50%
along the horizontal bar as per your diagram.

I changed the model for free space rather than over real ground but this
has not helped the directional aspects of the plot.

The dimensions were scaled form those shown for a 150MHz open ended
J-pole shown on Arrow Electronics site

http://www.arrowantennas.com/j-pole.html



Roy Lewallen wrote:
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