On Tue, 18 Feb 2014 18:10:39 -0500, "Ralph Mowery"
wrote:

I don't know which one would be the best but I have seen 3 methods of
feeding the J-pole. If you insulate the bottom then you hook the feedline
to the bottom with the center of the coax to the long side. If you do not
insulate the bottom you tap up the matching segment so that you get a 50 ohm
(if that is the coax used) match with the center of the coax connected to
the long leg. Then there is the balun made out of coax that is hooked up to
the matching segment so that a low swr is obtained.

There's also the American Legion J-Pole or the Silicon Valley
Emergency Communications Systems J-Pole:
https://picasaweb.google.com/112916124640757906440/NonarthopodicAntenna#5459396072666399154
https://picasaweb.google.com/112916124640757906440/NonarthopodicAntenna#5459396111364421106
This design does one thing right that none of the other J-Pole
mutations seem to consider. The length of the wire between the coax
connector center conductor and the driven element is an inductor. In
order to tune out this inductance, one needs a series capacitor, with
the inductor and capacitor tuned to the operating frequency. In other
words, a gamma match. The series capacitor is formed by the insulated
turns of electrical wire wrapped around the driven element.

Another thing this design does right is use the zero current point at
the bottom of the antenna as a ground. The problem is that it also
extends the length of the center wire, which makes using a gamma match
all the more important. I think putting the 50 ohm feed point and the
corresponding ground close to each other were either to reduce the
inductance of the connecting wire, or some manner of mutation from
when it was fed by a balance line.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558