On Sunday, February 10, 2013 11:47:11 AM UTC-6, Jeff Liebermann wrote:

Did you perhaps mount the antenna over a metal roof or on a tower side

arm? Without the decoupling section, the ground under the antenna

will cause pattern uptilt.

Nope.. It was a mounted on a metal mast that was on my
non conducting roof. Probably about 30 feet off the ground or so.
I think most of the skewing in my case was due to feed line
radiation, more than effects from the ground.




Thanks. That explains a few things. Incidentally, my rule "The

uglier the antenna, the better it works" was originally based on the

isopole antenna.

They were kinda ugly, but they sure worked well.
And some other companies have used that type of decoupling,
but most were more like cylinders, instead of funnel like cones.
Those were fairly common on some of the commercial verticals
used for public service, etc..
Also, most of those were 1/2 waves. IE: 1/4 wave upper radiator,
1/4 wave lower cylinder to complete the antenna, and then a lower
1/4 wave cylinder below that one for decoupling.
I think "Dodge" was one company that made those if I remember right.
The upper part of each cylinder was closed, and the bottom open.