If you're back five wavelengths from salt water or salt marsh, almost the
entire Fresnel zone will be over land and the salt water will make
essentially
no improvement . That's okay if the land is salt marsh, but its very bad
if
it poor sandy soil... For a take off angle of ten degrees, the near edge
of
the Fresnel Zone is about 0.1 wavelengths from the feed point and the far
edge is about three wavelengths away. For lower angles the far edge of
the Fresnel Zone extends out the 5 wavelengths or more.
For horizontally polarized antennas high above earth, typical for Yagi's and
such, saltwater under and around the antenna does not mean all that much.
The primary benefit is an unobstructed horizon and antenna height.
As for ground conductivity, unless it is terrible, what happens out at the
first bounce back from the ionosphere has more meaning. The 40 meter signal
from here is evidence of that.
Verticals on groundwave are a different story, as are verticals on bands
with very low wave angle propagation, where the Fresnel region phase change
can hurt low angles.
I would worry more about the path, and especially local noise. Things that
happen very close to the antenna can be handled with copper.
Of course if the goal is to broadcast on groundwave with vertical
polarization (the only mode that supports groundwave), a saltwater path is a
major improvement.
73 Tom
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