[TowerTalk] Precipitation static
k1ttt at verizon.net
Wed Apr 22 07:54:10 EDT 2015
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 at 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.
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