> and Jun 1997. The diameter of the radial wire makes a tremendous
> difference concerning ground loss. I've sed small gauge (#20 etc),
I've never seen any measured data (where the correct parameters were
measured) that indicated wire size is important to radial loss. The
primary reason size is not important is easy to see, if we look at
the problem in proper perspective.
First, consider loss in the antenna itself. It is very well known
that the power dissipated in even relatively small wire in an antenna
is negligible, as long as current levels are reasonably low.
Next, think about what a radial does and how it interacts with the
medial around it. The radial system can NOT have more current than
the antenna "pushing" against it, so I^2 losses in the conductor
itself are even less of a problem than in the antenna.
The bulk of losses in any radial or radial system are coupled losses
to the earth itself, and only **distance** reduces that coupling.
When we add multiple wires (spaced some reasonable distance apart, so
the wires couple more to earth than to each other), we decrease the
current and voltage density in any given cross-sectional area of
earth below the radial system, and lower losses.
If you want to observe this effect, model two parallel Beverages a
small distance apart. You will see the "gain" doubles with relatively
close spacing, while the pattern, S/N ratio, and directivity remain
essentially the same. The gain doubles because loss halves, because
the pair of antennas divide power and reduce field density and
losses.
Now make the individual antennas thicker, and watch the gain. You'll
find it has almost no effect at all on loss, changing primarily only
the impedance of the system.
We can be easily misled with all the hyperbole about "isolating
displacement currents" and looking at impedance changes in a complex
system. Sometimes we even install a good ground system, then never
actually make a connection to that system in the hope that the lack
of a connection will reduce loss!! Sound contradictory? It does
because it is contradictory. If you install a good
ground, use it with a direct connection. You have everything to lose
and nothing to gain by intentionally having a poor connection, or
intentionally concentrating fields with elevated radials, when you
have what would be a GOOD ground system below the elevated
radials.
All we really want to do spread the current and voltage out over a
very large cross section or area of earth, and we can do that only by
using a radial system that keeps field density low by spreading it
over a large area of earth. Making the conductor thicker, insulating
it, or shortening it and loading won't help decrease the field
intensity below the radial.
Increasing the height a large amount compared to the radial length
and operating wavelength will help, but really isn't much different
than simply using more wires in a regular easy-to-maintain radial
system.
73, Tom W8JI
W8JI@contesting.com
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