[TowerTalk] Fwd: Interesting Site

[David Robbins]

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 at arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373



-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Hans Hammarquist via TowerTalk
Sent: Sunday, June 25, 2017 21:32
To: towertalk at 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 at arrl.net>
To: Towertalk <towertalk at 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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