Hi, Robb
The antenna will still need some kind of counterpoise, one possibility
being radials. Radials are not the only form of counterpoise. An
alternative useful to this specific case is an FCP, short for 5/16 wave
single wire folded counterpoise. See w0uce.net/K2AVantennas.html if you are
not familiar.
An FCP, with a 66 foot linear footprint, parallel to the cliff edge and
elevated 8-10 feet will allow the vertical to do its cliff-side improved
performance without wiping out the cliff-side gains with a lossy
counterpoise heating dirt. Dropping the vertical down the cliff will still
keep it close to the cliff, with the same loss issues as a *very* low
dipole. If the location gives you a way to go *up* with the vertical, the
vertical over an FCP will do well.
We already have FCP installations of this general sort in the Caribbean
which have freed up the vertical aerial wire to do its ocean overlook
thing. These were a pleasant and significant improvement over the same
aerial wire over previous radial schemes made lossy by odd non-uniform
radial schemes forced on the installer by the non-flat and irregular
aspects of the otherwise superior location.
Without help, any wire carrying RF that is near to dirt, stone, etc will
induce lossy currents in same. A commercially efficient radial installation
is not possible for a cliff edge installation, because the radials hanging
over the edge would be out of balance with the horizontally oriented
radials.The efficiency of radials derives from being in the same plane,
full size, dense and uniform all around, as demonstrated by commercial AM
broadcast radials and their well-known, proven antenna system efficiency.
The point of an FCP is a folded design that produces RF fields that are
very close to net zero at nearby dirt and dielectric materials. An FCP does
not need the circular design for efficiency, instead deriving its
efficiency from the design of the folds in the single wire.
73, Guy K2AV
> > I live near a high cliff overlooking the sea. The cliff faces south, is
> a good 100ft high and is made up of mud and clay that over the years has
> been collapsing into the sea. I am considering mounting my Topband dipole
> as a vertical antenna above the cliff edge with the ground portion of the
> antenna going down the cliff edge below the vertical portion. I'm aware I
> may need to add radials but is there anything else I should need to
> consider. This is in preparation for the Boxing Day Stew Perry contest.
> > Thanks for your help.
> > Robb
> > G0URR
>
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