Robert,
You only have to "connect" to the salt-water. Don't worry about radials or
field of radials. From you coax shield, or whatever GND (common) you have,
run as many wires as you can into the water. They do not have to be long:
you just want about 6' of wire in the water (even at low tide). (RF does not
go far in salt water. You need to have the wires in the water to make them
(capacitively) couple to the water. You need many wires to get a low
impedance connection.) Of course, if you can tie to a large metal object
that is in the water, you will need only two or three wires in parallel.
I normally use #14 THHN with rocks (or other weights) tied to the ends. Four
wires will do OK, but 6 - 8 would be better.
Look at this: http://pt0s.com/index.php?page=photo&shot=antenna_wave
GL and 73,
George
AA7JV
On Wed, 8 Jan 2020 22:30:05 +0000
Robert Fanfant <rfanfant@hotmail.com> wrote:
Am looking to activate a location with very limited space surrounded by ocean. Think
of a small rock surrounded by saltwater/ocean. The vertical will be a tall
60’+ fiberglass pole and made to resonate on 160m. I would like a way to reduce
the required space of the 160m antenna radial field due to the limited physical space
available. The vertical will be located at the waters edge, or even possibly over the
oceans surface. At the feed point, will be a choke designed for 160m. We should also
assume maximum power of 1.5KW being fed into the vertical and the activation will be
for a 2 week duration of time.
One idea that came up is to use a floating piece of conductive material as the verticals counterpoise. Specifically, a thin conductive plate designed to float on the oceans surface. From the antenna’s feed point, will be a short length of ground wire say about 6’ long,
to this conductive plate.
Question(s):
1. Is it possible to just use the ocean as the ground plane / counterpoise ?
That is, can this idea work?
2. If so,
* How do I determine the required square footage/size of the plate?
* What material should be used as the conductive plate? (Nickel, copper,
aluminum, etc..? )The thought here is to make this plate as light as possible,
yet effective. It will need to last the duration of the activation (~2 weeks)
in/on saltwater, it needs to handle 1.5KW at the feed point, and likely exposed
to air and saltwater as it floats on the ocean surface.
-rob N7QT
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