[Lowfer] Active Whips and Rubber Sheets

[Les Rayburn]

At 09:51 AM 2/2/02 -0500, you wrote:
> > Many of you are no doubt familiar with the "rubber sheet" theory that
> > states to avoid electrostatic fields and obtain maximum performance
> > from any active whip antenna, you need to place it at the highest
> > possible point in the area.
>
>I'm not familiar with that theory, but would like to be.
>
> > 1. In your experience, am I likely to achieve much more performance if
> > I place the whip on top of the 40 foot mast?
>
>This is identical to my work with small vertical probes for 160
>meters.
>
>How do you divorce or choke the mast and feedline from the active
>whip? If you do not effectively electrically isolate the two, which is a
>very difficult task, all you do is create a larger (longer) antenna.
>
>How is the active whip isolated from the feedcable and the
>mounting, and what does it use for a counterpoise?
>73, Tom W8JI
>W8JI@contesting.com



I don't know all the details about the theory either, but in a nutshell it 
basically states
that for best performance an active whip needs to be the highest object for 
at least
a 1/2 wavelength at the lowest frequency of operation. Hard to do at LF, so in
practical terms the advice is usually to pretend there is a "rubber sheet" 
pulled
over your property and make sure the whip is the highest point.

My whip is mounted currently on a metal mast, with the last six feet being 1/2"
PVC with a wooden dowel inserted for strength. The feedline is isolated
using a torroid. Currently the whip does not use a counterpoise at all, though
I plan to install a virgin ground at the base of the mast soon to see if that
improves performance.

I'd love to hear more about your experience with active whips on 160 
Meters. Mine
is tuned active whip, using a litz wire inductor, designed by Bill Bowers. 
Very sharp
"Q" which makes it perfect for LF work, but perhaps a bit too sharp for
work on 160 meters.

73,



Les Rayburn, director
High Noon Film & Interactive
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