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[TowerTalk] Length of Mast

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Subject: [TowerTalk] Length of Mast
From: (Jim Rhodes)
Date: Sun Jun 1 16:28:20 2003
Years ago I heard W0UN's presentation at Dayton where he claimed that when 
a thunderstorm would move over his multi-tower setup in Colorado that the 
lightning would actually stop until the storm front would move beyond the 
antenna farm. The towers were heavily grounded as I recall, but I don't 
remember what else he did for lightning protection. I don't think he left 
much undone on that front. This would support the theory of lightning rods 
to prevent lightning strikes. And that is what I learned years ago in a 
college meteorology class.

At 10:50 AM 6/1/03, Joe Giacobello wrote:
>You guys have raised an issue that I have wondered about for some time 
>now.  I also live out in the country and have noticed that the number of 
>houses and other structures with lightning rods seems to have diminished 
>over the years.  Why has the use of lightning rods fallen out of favor?
>It was always my belief that the purpose of the rods was to slowly and 
>continuously bleed off electrical charge in the air so that the likelihood 
>of generating a voltage in excess of the the breakdown voltage for air in 
>the vicinity of the structure was minimized.  The ultimate objective was 
>to prevent a sudden, instantaneous, potentially destructive, high current 
>discharge through the structure itself.  When I proposed on the Antennas 
>mailing list that this mechanism most likely also applied to a properly 
>grounded tower near one's house, my description was corrected by one of 
>the readers.  Apparently, the effectiveness of the rod or tower depends on 
>the formation of a cloud of charge in the air surrounding the tip.  In 
>windy conditions, the cloud becomes unstable and must continually 
>reform.  (Although I'm not sure that it makes any practical difference, I 
>was also informed that the flow of charge was from the ground through the 
>rod into the cloud.)  Is it because windy conditions reduce the 
>effectiveness of lightning rods that they are less used today?  I'd be 
>interested  in hearing some comments on this question.
>I should also add that I have a pointed multiwire attachment strapped to 
>the top of my tower which (allegedly) provides multiple paths for 
>discharge and reduces the voltage necessary for (slow) discharge to 
>occur.  (It can be purchased from the Wireman, and Pres swears that it 
>works.) I also have a pretty good ground system with about eight ground 
>rods connected in a large circle that includes the house ground.  I have 
>observed major lightning strikes on a ridge about the same height as mine 
>and about 3/4 of a mile away, but I have never been hit. Have I been lucky 
>or is the system really working?
>73, Joe
>Pete Smith wrote:
>>At 06:45 PM 5/31/03 -0700, Michael Tope wrote:
>>>Actually it brings up a good question for the lightning technology experts
>>>on Towertalk. How come you only see lightning rods on barns and not
>>>houses? Is that just because most barns are old, and people have stopped
>>>using lightning rods, or is the their some other reason?
>>My house -- a farmhouse -- came with an array of 6 lightning rods, 
>>complete with woven aluminum down-conductors.  Lightning rods are fairly 
>>common on houses out here.  I am very unclear on whether they offer any 
>>protection at all, because the ground conductors seem to violate the 
>>low-inductance requirement that we hear from Polyphaser.
>>It's not clear to me why lightning would "prefer" the rods to other 
>>ground conductors that might be available in the neighborhood, or on 
>>nearby power poles.
>>73, Pete N4ZR
>>The World HF Contest Station Database was updated 9 May 03.
>>Are you current?
>>See:  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
>See:  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

Jim Rhodes K0XU
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