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Sorry for the spelling error crystalls should be crystals. When lightning
hits the Earth, the heat it generates is enough to make glass which is an insulator. The ground rod becomes isolated from the Earth. If you spread out the contact area with the Earth as with the fence around the perimeter of the property, then the energy is not concentrated to one spot. The over all impedance is also much lower. I would install a ring grounding system around the tower. A 32ft. diameter ring would do nicely in a clay/rocky soil. Place 8ft. ground rods in the ground every 16 ft along the 32 ft. diameter circle (approx. 6 rods). Each rod is then connected to the tower base with a multistrand 00 copper wire and a ring of 00 copper to connect each rod together. The connections should be cad welded or at least treated with a deoxit coating to prevent corrosion. I have had excellent luck with this approach, no lightning hits and my tower sits up at 870ft. ASL or 650 ft. above average terrain. Note: the tower has a strike counter hooked up to it so I know no hits have happened. Go to this link to read more http://www.polyphaser.com/ppc_pen_home.asp . Frank N1SIF "CIL" wrote in message ... I would suspect a poor grounding system on the tower. If the ground is a rod driven into the Earth, then the impedance needs to be as low as possible. Once the ground system takes a surge, glass (( (crystalls?))) will formin the dirt on and around the rod. The impedance then climbs and the numberof strikes to the tower increase. The amount of impedance in your groundnetwork determines the amount of static charge that can build on the towerand how fast the charge can bleed. (((The tower sites are only about 100 feet apart, ground substance is the same, clay/rocks, 1st foot then clay.. The first tower ground, is a 4 ft hole, with ¾" rebar then driven deeper,1.5ft, w/ horz bars 1ft on center from bottom of hole to top, where a ¾ steel plate was welded to vertical bars, and to the plate, strong hinge plate connected to 25 rohn tower. The 'other site', is two 4" pipe, 5ft, in the ground, and welded to fence. Fence is 2"2/8 upset tubing that goes around property/everything welded. ((fence is 5 foot tall) and as stated part of the 'gournding system',,,? The first 'site' was not connected to the primenter fence,,problem???)) If you are familur with the ''bird tilting over and drinking from the cup", you can picture in your minds eye, my 'tilting tower'. It is about 75ft tall, with a uhf/vhf duel band at top of mast, four ft. below that is a two meter horz omni ground plane.))) Can you describe how each tower was configured at the top and how it was grounded? What is important to know if the top ended up with sharp point (mast, VHF vertical antenna, etc.) or Yagi type antenna, like tribander etc. without anything pointy protruding above. Yuri, K3BU ((( Both towers carried almost the same 'items', vhf/uhf , and 4 ft below that, clover leaf horz ground plane.))) but their tower lighting chokes kept lightning off the a-c power source. ((( What do you call these chokes, I know I have read about, but at the moment I am blank.))) The broadcaster starts his lightning protection at the tower top with a small lightning rod extending above and beyond the beacon to take the hit and avoid expensive repairs at the tower top. ((( Is this something like the antennas I have seen that have a 'center core' copper rod???))) Tower guy insulators are doubled and tripled where they connect to the tower so that static breakdown occurs to the earth instead of at the tower. ((( Where do I 'see/read' about this??))) One such line was on a small single story U-Stor-It building between two very tall radio station towers, that was assumed to be lightning proof due to it's location. It was hit and hit hard when neither tower was hit .."How did your team "know" what was struck? """.my question was and is,,,, why? (((((((((((((((((((This statement is the one that makes the most sense to me))))))))))))))) Lightning is Female. 20 million volts & 100 thousand Amps will do as it damm well pleases! ((((Last, but not least,,,,,,, thank you, WILL implement input, cl&73)))) |
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