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## Re: [TowerTalk] Grounding a vertical

 To: "Mike Bragassa, K5UO" , Re: [TowerTalk] Grounding a vertical Jim Lux Sun, 26 Mar 2006 07:39:43 -0800
 ```At 06:43 AM 3/26/2006, Mike Bragassa, K5UO wrote: >...speaking of lightning: > >What is a simple and effective ground for my base-loaded 80 meter vertical >(Rohn 25g)? "Spark gap": How can one be made and what gap is correct? In a uniform field gap (which you are not likely to get, but more later), breakdown, in air, at sea level, is about 70 kV/inch (or 30kV/cm). Almost any practical gap will breakdown at a lower voltage, depending on how nonuniform the field is, how rough the surfaces are, etc. A sphere gap (two smooth spheres separated by much less than the diameter of the spheres) will have a breakdown slightly lower. There's no simple analytical equation for it, so most resort to tables (http://home.earthlink.net/~jimux/hv/sphgap.htm for the design of the gap and http://home.earthlink.net/~jimlux/hv/spherev.htm for the table). A needle gap (basically, anything with reasonably sharp points) will breakdown at about a third the voltage of the uniform gap. call it around 25 kV/inch or 10kV/cm. Below around 350V, gap breakdown won't occur, regardless of how low the pressure or spacing. (http://home.earthlink.net/~jimlux/hv/paschen.htm) If your air density is lower than standard sea level, the breakdown voltage is reduced proportionally (at 18,000 ft, the breakdown will be half, at 5000 ft, about 80%) The challenge in RF applications is getting a gap that has a close enough spacing to breakdown at a low enough voltage, but that doesn't have significant L or C, so that your circuit isn't perturbed. A couple bolts with the right spacing works fairly well, and is reasonably adjustable. >Thanks! >Mike, K5UO >_______________________________________________ > > > >_______________________________________________ >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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