Cecil Moore wrote:
As a point of interest, what is the feedpoint impedance of a 2m
J-Pole if the short is removed at the bottom and the antenna is
fed at that point, aka the original Zepp antenna? Is that like
the Arrow Antenna's J-Pole design?

Just measured the Arrow Antenna J-Pole and can report that it
*is* a Zepp design scaled for 2 meters. Here's the schematic:

Center
Conductor---------+
1/4WL + 1/2WL
Braid---------+--------------------

The center conductor and braid are usually reversed for a Zepp
but that really doesn't make a whole lot of difference. The Arrow
Antenna J-pole just uses an open stub instead of a shorted stub
like the average J-pole. The 1/4WL open stub transforms the very
high feedpoint impedance of the 1/2WL section down to a low
feedpoint impedance. The 1/4WL shorted stub of the average J-Pole
transforms the impedance from zero ohms at the short to thousands
of ohms at the base of the 1/2WL section. Somewhere in between
those two values lies the desired value of 50 ohms so the shorted
stub has to be tapped.

Actually, I think I like the Arrow Antenna version better for
homebrewing. The 3/4WL section is bolted to the base plate which
is easy. Then an SO-239 can be mounted on the base plate for attaching
the coax and a 1/4WL #14 solid wire can attached to the center of the
socket and be supported at the top by an insulator attached to the
3/4WL section. The Arrow Antenna version can be mostly aluminum while
the ordinary J-Pole, being 100% copper tubing, is relatively hard to
solder.
--
73, Cecil, http://www.qsl.net/w5dxp