Topband: Salt-Water Qth!

[Tom W8JI]

> 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