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.
Apr 22, 2015 06:53:25 AM, rstealey@hotmail.com wrote:
Tom has a good description of this phenomenon at
http://www.w8ji.com/pecipitation_static.htm (Yes, it is spelled wrong on the
site)
I am experiencing it exactly as he describes, on a 40 m beam that is mounted 5
feet below a 3 element Steppir. No noise on the Steppir.
Is p-static different than plain old static buildup, which I always assumed was
drained off by a resistor in my lightning arrestor?
Tom seems to say there is essentially nothing that can be done, other than to
lower the antenna or redesign it to eliminate any sharp points, so my concern
is what damage can this do to my rig? It's easy to say don't use the
rig/antenna when there are storms, but how would you know until it's too late
in the case of an approaching storm? My lightning arrestor has an R and gas
tube to ground. When it first occurred I didn't realize what it was, until it
abruptly ended when a strike occurred. The beam was connected to my TS-590 and
there was no damage.
Rick K2XT
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