You know I keep reading the stuff on those and this pdf started to make some
sense on what the thinking is about those porcupine things. First, they will
NOT prevent lightning strikes, that has been proven... for those of you not
interested in some other thoughts stop reading NOW!
This reference pdf talks about dissipating static from airplanes and from van
de graaff generators. In both of those cases I will agree that spiky
dissipators will work. In both airplanes and van de graaff generators the
surface area is relatively small, in the generator case maybe a couple square
feet, in airplanes maybe several hundred or a couple thousand square feet of
charged surface. In either case the accumulated charge from either wind or
friction charging is relatively small and builds up slowly... on planes because
they are insulated by lots of air, and on the generator because of the
insulated post. In either case it is fairly easy to cause a flow of ions that
dissipates the charge, in the case of the airplane its not even necessary to
get rid of all the charge, just enough to prevent corona around the antennas.
A dissipator may actually do something to help prevent static build up from
wind blown snow or sand, has anyone tested them for that?? a tower being
charged by wind blown snow or sand may work more like an airplane since the
amount of charge built up is relatively small.
The problem comes when you try to scale that up to dissipate the charge induced
from a convective storm. In the case of convective storms (with or without
lightning) there is a large pool of charge in the base of the cloud often
several thousand feet up. this large charge attracts the opposite charge on
the ground which is essentially an infinite source of charge being drawn toward
the cloud. There is of course no way a dissipator can affect that charge
except very locally, and they may actually be good sources of the upward
streamer that connects with the downward leader resulting in a lightning stroke
to the dissipator itself.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Hans
Hammarquist via TowerTalk
Sent: Sunday, June 25, 2017 21:32
To: towertalk@contesting.com
Subject: [TowerTalk] Fwd: Interesting Site
This topic has been discussed too may times and there seems to be nobody with a
definite answer. I have dissipators on my own tower. They are rather easy to
make. I haven't gotten any lightning strikes in them during the few years the
tower been up. That doesn't mean they are effective. I have notice that I have
had no strikes on my house, something that happened on a relatively regular
basis, since the tower went up. I think the tower itself was the contributing
factor to that, though.
I had a 0-0, stranded aluminum cable at hand when I raised the tower and
decided to put three, one on each leg, of them up. You can view they on my
facebook page. Does it work? Honestly, I have no idea. I do think that you can
build these dissipators yourself for a much lower price than what they are
offered at.
With 73 de,
Hans - N2JFS/SM6BXX
-----Original Message-----
From: Don W7WLL <w7wll@arrl.net>
To: Towertalk <towertalk@contesting.com>
Sent: Sat, Jun 24, 2017 11:25 pm
Subject: [TowerTalk] Interesting Site
Ran across this looking for something else and noticed a section on towers,
grounding and other items we are all interested in. Sample article.
http://www.thebdr.net/articles/steel/twrs/TT-dissipators.pdf
Don W7WLL
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