> Al Williams wrote:
>
> > Can Towertalkers explain why antennas over salt water is such an
> > improvement?
> >
> > ..snip..
> >
> > What else is happening?
>
> It is very difficult to get a good ground in dirt. Youneed at least 64
> 1/4 wave long radials. In salt water you can throw out a 6 foot bare wire
> and have an excellent ground.
>
> Chuck, W5PR
Hi Chuck,
Skin depth of saltwater on 160 meters is in the range of a foot or
two. If you throw a six foot wire in the salt water, you have
something far from an excellent ground. Only the top foot or so of
the wire (less on higher bands) is coupled to the water!
The current density, if that was your sole ground, would be so high
the losses would be high. As a matter of fact, a small volume of
salt water makes an excellent dummy load!
If I laid a 100 foot radial off the shore into the salt water, only the
first few feet would have any useful effect. The rest would just
irritate the fish.
The proper method of connection, if you want low loss, is a non-
resonant screen suspended ABOVE the water or a modest number
of radials above the water, extending out for something near 1/8 wl
or so. That will "spread" the current out so the I^R losses are low.
Salt water is certainly much better than dirt, but it is not copper!
You can't jump start your car with a saltwater soaked rope, or even
light a small lamp! It certainly is excellent in the Fresnel (don't say
the "s" in that word) zone, but watch out if you make the current
density too high by making the connection at a single narrow point!
73, Tom W8JI
w8ji@contesting.com
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