|To:||"Tom Rauch" <email@example.com>,"Charlie" <firstname.lastname@example.org>, "Bill Shell" <email@example.com>,"Tower Talk List" <firstname.lastname@example.org>|
|Subject:||Re: [TowerTalk] Conductive Concrete and Grounding|
|From:||"K8RI on Tower Talk" <email@example.com>|
|Date:||Thu, 27 Jan 2005 12:38:15 -0500|
Although lightning is DC (static electricity) is does tendto "ring" with astrike consisting of both positive and negative currentflow.
I agree. The fast rise time creates a wide range of frequencies. The amplitude does drop off rapidly with frequency, but I believe it is still strong at 1 MHz and can be heard up into the microwave range.
Like any wave with fast rise and fall times there is a lot of power outside the primary range if memory serves.
I do think the majority of damage comes from either the power or telephone lines and not the antenna system.
modems or anything else inside any building, including a GAsFET preamp on a repeater that was on that 7/8th inch cable AND I don't have a single Polyphaser or other lightning protection device on any feedline.
I had one hit on the old tower that blew off all the water proofing and even removed the plating from every connector at the top of the tower. It left the repeater antenna looking like an exploded cigar, but did nothing to the old TH-3. It did take out the front end on one 2-meter receiver and blew out the 7/8" heliax about 30 feet below the top of the tower. It didn't hurt the old repeater.
That tower only had about 8, 8' ground rods and roughly 150 to 200 feet of bare #2 for a grounding system. It was also at the back of the garage which meant the ground system was not symmetrical with nothing to the East. Then again, it was a painted tower which would have had fairly high resistance between sections.
I some times wonder if the added insurance of the poly phasers is worth the effort.
Roger Halstead (K8RI, EN73 & ARRL Life Member)
N833R, World's Oldest Debonair (S# CD-2)
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.
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