|Subject:||Re: [TowerTalk] CDwelding a tower leg|
|Date:||Mon, 17 Sep 2012 18:58:58 -0400|
On 9/17/2012 11:33 AM, Frank wrote:
I'm still an amatuer with 60 foot tower and 4 element beam located in a secluded valley. Your set up sounds professional. You have more steel in the air than my zoning laws would allow.
The theory: An overhead charge moves along through or with the clouds.An opposite charge moves along on the ground. The charged area on the ground maybe hundreds of yards across. Towers, trees, and power lines provide vertical extensions to this charge. The static does not just build up on the tower or antenna, that is only an extension, and/or connection to a much larger charge.
Because the tower is part of a charged area the static usually does not build up "on the tower" which makes it quite different than precipitation static building on an ungrounded tower. Snow on a cold and windy day can turn the ungrounded vertical or tower into one whale of a Van De Graaff Generator with startling results at the other end of the coax that could put the most powerful ignition system to shame.
The tallest object might be the most likely to take a hit, but it is only a tiny bit closer to the overhead charge than the surface. So it's not good to go against the odds, but those same odds come with no guarantee.
The one predictable thing about lightning is its unpredictability.It was 130 feet to the top antennas in http://www.rogerhalstead.com/ham_files/Tower29.htm
which I've shown many times. I've also said that the tower and antennas took 17 visually verified hits the first 6 years it was up. It has taken none the last 4 that anyone has seen.On several occasions nature must have had poor aim as a stroke completely ignored the tower and hit a power pole just to the North and East out by the road. That strike was almost at a 45 degree angle to the top antennas. It wiped out a bunch of stuff in their house including the transformer on the pole IIRC. It also hit a young spruce tree about 100 feet to the East of the road with largest piece being about 3' long. There have been other "close ones" that did not hit the tower.
73 Roger (K8RI)
No wonder you got hit. You have my sympathy and envy. Cqtestk4xs@aol.com wrote:I assume you don't live in the lightning capitol of North America, central FL. I understand very well about lightning and static build up as do others who have posted here. I have three 199.99 footers as well as several other smaller ones. Unless you live in an area of little t-storm activity you have been very lucky. Having a lightning hit your tower is not if, but when. I have spoken to several EEs who work at the local surge protection mfg company and since I have followed their advice I have had no damage even though the towers have been hit over the summer. Bill K4XS/KH7XS In a message dated 9/17/2012 2:53:22 P.M. Coordinated Universal Time, email@example.com writes: Nope, never been hit by lightning in over 30 years of hamming. Evidently you have had that misfortune. Ever wonder if there might be something you don't understand about static build-up? My tower is grounded by virtue of the tower leg bottoms stuck in sand and dirt below the concrete. I don't need any additional grounding. The tower acts like a big lightning rod. Contrary to popular belief, lightning rods don't attract lightning, they dissipate static charge. At least mine seems to work that way. Your milage may differ. Cqtestk4xs@aol.com wrote:You ever take a lightning hit? I have several times and it was uh....exciting. Towers were extensively grounded but not to a commonground with thehouse. Three tower legs are not an extensive ground and will not dissapate a direct hit and will likely make a beeline to your shack onthe coax tofinish the job on its way to your home grounding system through thehouse.You are living on borrowed time with that attitude. Extensive grounding is your best friend and the insurance company's. Bill K4XS/KH7XS In a message dated 9/17/2012 1:17:23 P.M. Coordinated Universal Time, firstname.lastname@example.org writes: I fail to see why a ground is needed at all. Surely the lower two feet of tower is firmly embedded in dirt with the concrete anchor above that. If it was done that way those three tower legs should serve as some pretty good ground rods. At least my version of common sense tellsme so. I will have to admit that common sense has not always been kind. Sometimes it does not make sense at all and becomes just common bs. I am wondering what it might be on this topic? Anyone venture a guess? _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk_______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk_______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk
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