Roy Lewallen wrote:
I put this aside until I could do a little modeling. A lot of postings
have been made in the interim, but I don't see too much in the way of
answers. I'll try to answer some of your questions.
Will wrote:
I want to set up a hf antenna for my sailboat.
I have read various guides from Icom etc.
They suggest running copper foil to a Dynaplate and use sea water as
the ground. How can this work when the Dynaplate is below sea water?
I don't know anything about Dynaplates, but if it's on the hull, it's
very near the surface of the water. Any current it conducts will flow
along the top of the water displaced by the hull. If, on the other hand,
it's really under any depth of water at all, it'll be invisible to RF
and might as well not be there.
Roy, after re-reading the above comment this morning, I realized you
probably meant that RF currents flowing to the plate could simply travel
from the plate along the hull/water boundary to the water line, and from
there, change direction and travel over the water's surface. Much as
currents would travel up and down the surface of a large ocean wave
(except for hull/water vs. air/water boundary differences).
If so, then your model results show the Dynaplate's location is not
critical as long as it is attached to the hull and it need not be
mounted at the waterline?
Is my reading of your comment correct?
Thanks.
73,
Chuck
Is sea water equal to copper wire radials as a RF ground system?
Yes.
Does sea water make a good enough ground without radials?
Yes. A foot-long wire "ground rod" below the antenna provides a nearly
lossless ground connection at HF.
How can a piece of copper metal about 1 ft square equal several
radials laying on the boats deck?
Radial wires are used for land based systems because of the poor
conductivity of soil. Radial wires reduce the resistance of the path
current takes going to and from the antenna base. Salt water is a good
conductor and doesn't need -- and won't benefit from -- radial wires.
Why do i have to use copper foil when most other people suggest using
ordinary copper wire?
You don't. And won't copper corrode rapidly in salt water?
Over seawater what would be the best number of radials to use
considering that maximum length i can run is 40 ft. I am planning to
use a backstay antenna with a SGC 230 Tuner.
None. A simple wire down into the water is adequate. Or use a small
plate very near the surface if you prefer.
Roy Lewallen, W7EL
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