For receiving, an absence of noise sources in the path is all the difference
in the world. As an example of this look at what N7JW and K7CA did from the
Utah desert area. Utah desert is like the anti-saltwater, and they are
located much further from Europe than the east coast with a worse polar area
path, yet they had outstanding results. Saltwater has the same advantage, as
do freshwater bodies, of a lack of noise sources in what might be a desired
direction.
For efficiency (which only affects transmitting), the advantage is primarily
concentrated at low angles and primarily affects vertically polarized
systems. The question then becomes one of wave angle and polarization.
Then there is distance as a factor, and path loss related to the magnetic
poles, which are factors.
A good station has a combination of everything going for it, but there is no
magic and there certainly isn't any 10 dB or more involved just from being
near saltwater. A few dB here and there from multiple factors are what make
the difference. Move 25% or 50% closer, get rid of noise sources in the
path, increase vertical antenna performance at low angles a few dB, and get
away from going past the magnetic poles and it is a winner. It isn't from
magic, and it isn't all from the presence of saltwater, and it is not 10-20
dB by any stretch of the imagination.
73 Tom
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