Reflectees, W8AV meant the following for the reflector rather
than direct to me. He asked that I forward same.
--------- Forwarded message ----------
From: W8AV@aol.com
To: aa4nn@juno.com
To: <tentec@contesting.com>
Date: Tue, 14 Sep 1999 06:49:58 EDT
I guess I will add my two cents worth to thgis thread. The object of a
ground system is to minimize system losses caused by the poorer
conductivity
of the soil. In the U.S. the theoretical soil conductivity ranges from
about
30 mS/m (pretty good) to 0.5 mS/m (very poor). Thus, we add ground
radials
to a vertical antenna to help the soil out a bit to increase the
conductivity
in the near field of the antenna and thus reduce the return current
losses in
the antenna system. The highest losses are most often seen right at the
base
of the antenna itself. By adding a ground screen around the base of the
antenna, the return current losses are significantly reduced resulting in
an
increased radiation efficiency of the antenna system. After all, we all
want
to radiate every last bit of RF energy possible when trying to snag the
new
one on top band.
So, add the ground screen. Remember however, if you use galvanized
chicken
wire make sure that the connections are clean and bond this screen to the
existing ground system with a silver solder. Regluar solder will break
down
with the weather and render the connection unusable in a year or two.
Better
yet, if you can find a local AM broadcast that is replacing its ground
system, see if you can get some of the scrap pieces of expanded copper
mesh
screen to use as your ground screen. This way the electrolytic action
that
occurs beterrn disimilar metal (i.e. copper and galvanized steel) will be
avoided.
Finally, an alternative to the ground screen that works almost as
good
as a screen (the screen by design is by far the best) is to intersperse
short
ground radials between the existing radials of the ground system. For
example, if your existing ground radials are 100' long, install some 50
footers between each of the long radials. We have used this technique in
the
broadcast industry with good success in cases where the station could not
obtain/afford to install copper screens.
73...................de Goose W8AV
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