Topband: Unique Short Radial Challenge
Dan Zimmerman N3OX
n3ox at n3ox.net
Sun Oct 21 09:24:57 EDT 2007
>as the water level
>increased, there would *always* be some connection between water level and 7
>inches beneath it :-)
Salt water is a great RF conductor as far as things that are laying on
the surface of the earth go ... versus dirt, rocks, etc, it's great,
but it's still over 10 million times worse than copper.
I find here http://lakeaccess.org/russ/conductivity.htm that seawater
is about 4.3 siemens per meter, and at matweb.com I find the
resistivity of copper as 1.76 * 10^-6 ohm*cm, and that makes the
conductivity nearly 57 million siemens per meter.
(you can see this in the relative skin depths, which are measured in
microns in copper)
I mention it because I think a wire or two that abruptly dive below
the water surface are essentially going to give you a couple of point
contacts into a material that's pretty highly resistive in absolute
terms. The resistance of those contacts isn't going to be very low.
I don't know the practical solution, but the best thing you could do
to connect to the salt water is have a whole bunch of relatively short
radials on floats so the entire length just rests on the surface all
I think that's why people recommend the two gullwing elevated radials.
Small numbers of low elevated radials tend to be lossy because the RF
field from them induces currents in the ground below and around the
base of the antenna.
Those induced currents are quite spread out, though, compared to what
you'd get if you just tried to drive RF current into point contacts in
the earth. A pair of slightly elevated radials over lossy earth is
much better than a ground rod, for example. Neither is great, but the
elevated radials are much better.
The spread out induced currents from a pair of radials right next to
the ocean, though won't cause much loss because the saltwater is 1000
times more conductive than soil.
It doesn't seem like adding a few wires into the ocean should hurt if
you have elevated radials, but you should read this:
and also this:
I think you should forget about the ocean connection, use a pair of
elevated radials and just enjoy the benefits of the nearby saltwater.
That's all you need for a killer signal from an oceanfront elevated
radial antenna, it seems
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