Rain static can be a real pain during a contest. Using only lower
antennas helps but in my station the static on these can still be pretty
strong. Perhaps my lowest antennas are not low enough. What do the big
contest stations use during rain static conditions? Is a SteppIR really
quieter?
John KK9A
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Precipitation static
From: David Robbins <k1ttt@verizon.net>
Reply-to: k1ttt@arrl.net
Date: Wed, 22 Apr 2015 06:54:10 -0500 (CDT)
precipitation static really doesn't require any precipitation or
lightning, it
is due to corona created by the high electric field under a convective cloud.
If the field gets high enough then lightning is likely to accompany it...
when
lightning strikes from such a storm it momentarily lowers the electric field
gradient which reduces or stops the static until the field builds again.
because the gradient is between the ground and cloud the higher the
antenna the
worse the corona. and having other antennas above reduces the gradient on
the
lower ones so lower antennas in a stack are often quiet when the top one is
noisy.
all grounded construction doesn't help because the charge causing the
corona is
not building up on the antenna because of triboelectric charging like you can
get with windblown snow or sand. in those cases the charge is put on the
antenna by contact with the snow or sand and can be drained by a resistor or
inductor. in the case of corona from the electric field it is actually the
cloud attracting the charge up the structure from the ground causing a
concentration near the tips of the elements. Since the charge is drawn up
from
the ground any other connection to ground through a resistor or inductor
won't
drain it off.
Most likely the steppir is quiet because it is essentially wrapped in
fiberglass which may help prevent corona by shielding the conductive parts of
the elements or just reducing the field gradient near the tips of the
elements... note that Telrex used to try to do that by adding balls to the
tips of their elements on some models... that didn't seem to help on the
ones I
had, I suspect because they still had lots of sharp points due to the screws
through the elements and corners on T-match shorting plates.
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