That model seems to work fine in EZNEC.

I tried a 918 MHz version with long length = 219mm, short length = 72mm,
24mm apart, 1.5mm solid aluminum construction.

The results show excellent SWR and feedpoint impedance close to 50
Ohms.(50.29 -j0.0148), SWR = 1.006
The unit is not so omnidirectional showing a front/back ratio of
5.79dB.(Beamwidth 214.4 Degrees).

The maximum gain was 4.74dB(ref) at 4 degrees (elevation). dB ref =
2.14dBi so I suppose this is saying gain is 4.74dBd.



Dan Richardson wrote:
On Sun, 18 Sep 2005 07:14:39 -0500, Cecil Moore
wrote:



The open stub J-Pole (Zepp) is modeled as a shorted stub
J-Pole with the source in the middle of the shorted segment.
Mine is for 53.2 MHz. On edge it looks like this:

13.5 ft.
+---------------------------------------------------
|
(S)
|
+-----------------
4.5 ft.

The sections are 0.1 ft. apart. The resonant frequency is
53.2 MHz and the feedpoint impedance is 25 ohms for an SWR
of 2:1. The feedpoint is 30 ft. high over high-accuracy
ground. The gain over ground is 6.2 dBi, omnidirectional.
Free space gain is 3.4 dBi.


You can vary the feedpoint impedance by changing (S).

73,
Danny, K6MHE

email: k6mheatarrldotnet
http://users.adelphia.net/~k6mhe/