To: | <towertalk@contesting.com> |
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Subject: | [TowerTalk] Re: Static, Lightning, and protection |
From: | Didier Juges <didier@cox.net> |
Date: | Mon, 22 Mar 2004 10:40:02 -0600 |
List-post: | <mailto:towertalk@contesting.com> |
At 09:50 AM 3/22/2004, David Robbins K1TTT wrote:
> > Good point. At higher altitude, the dielectric strength of air is > less, so the voltage cannot build up as much before the strike > starts, so the clouds cannot build as much energy as they > can in Florida. Maybe the generally dryer air in CO offsets the altitude's effect on dielectric strength. I agree that the change is fairly small. I design HV TWT supplies for, among other things, military planes (radar and countermeasures), and some of what I do is qualified up to 90,000 feet (most go to 65,000). I also do some commercial equipment. We typically consider 3,000 feet elevation to be ground level. Most commercial equipment is certified to 10,000 feet and does not require special precautions, considering everything we do is potted in silicone compound. Air insulated equipment is another story. A note on observing single storms. I have also seen the phenomena mentioned where lightning seems to stop before it reaches my station and then starts again on the other side. I agree. There are many documented examples of strikes in a valley between two ridges. Assuming the storm is a static thing that moves across terrain and only hits the highest point is a mistake. A good analysis of strokes to an area as small as a ham station would take many years of data, probably much more than is available in the current u.s. dataset. Even for detailed studies of power lines the minimum size data block we normally use is 10 minutes on a side (about 10mi) and we average the data over a 10 year period. There you go again, trying to confuse us with data :-) David Robbins K1TTT e-mail: mailto:k1ttt@arrl.net web: http://www.k1ttt.net AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
_______________________________________________ See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA. _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk |
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