[TowerTalk] Elevated vertical

[Jim Lux]

At 03:56 PM 10/4/2005, Tom Rauch wrote:
> > > Elevated radials SHOULD have the feedpoint decoupled
>through
> > > a common mode choke. if you ground the radial common
>point
> > > is causes increased loss as well as current on the
>feedline
> >
>To be truly unbalanced a system should have equal and
>opposite currents flowing into the shield and center
>conductor at both ends, and the shield has to have
>essentially zero voltage to the environment around the
>antenna including the feedline.
><snip>
>
>One of the things I didn't initially believe when I read the
>first article (based only on models) was an earth path would
>reduce antenna efficiency when using elevated radials. When
>I actually tested systems, I found it was true.

Interestingly, this is one of the test cases for NEC3/NEC4.. They had 
experimental data similar to your observation, NEC2 didn't show it, and 
they wanted to make sure the revised version did.


>I'm very skeptical of any system that is reported to clearly
>beat a system known and proven to have nearly 100% of the
>maximum possible field strength. Of course it is work to
>install 50 ground wires, and that alone is good reason to
>not use them if ease of installation outweighs the
>electrical disadvantages of small counterpoise systems.

I would venture to guess that a small number of radials could be made to 
work as well as a conventional ground system, for one frequency, at one 
time, etc., etc.

As you note, the fewer the elements, the touchier the system gets.