Roger that, Mark. A lightning diversion system needs its own low impedance path to ground because the huge currents involved can do strange and unpredictable things if they get into the building's AC power.
A full threat lightning attachment has millions of volts before the air path ionizes. Once the air path ionizes, its impedance is essentially zero and the current during the flash can reach 250 K amps. On average, the AC component of the lightning flash is around 125 KHz. You really don't want that kind of energy running around the buildings AC power wiring because there will be arcing nasties along with induced currents that can, and probably will, fry stuff like computers, TV's, etc. After a lot of years at Lockheed designing lightning protection for military aircraft, I've developed a very healthy respect for the stuff. You can sit there and calculate impedances, etc., until the cows come home, but when lightning hits, it's still not all that predictable. Use a DC grounded antenna and a dedicated path to a dedicated ground rod to divert as much lightning energy as possible away from the building's AC power system. Also, use the available braided lightning diversion cable from the lightning rod (in this case, your DC grounded antenna). The Polyphaser (R) will help, but a direct lightning attachment to your antenna will most likely destroy it. But, IMHO, it's better to sacrifice the antenna than the repeater and associated electronics. Lightning is like the 800-pound gorilla. It goes wherever it doggone well pleases. Dick ----- Original Message ----- From: "N9WYS" <[EMAIL PROTECTED]> To: <[email protected]> Sent: 30 December, 2005 15:53 Subject: RE: [Repeater-Builder] polyphaser Help I think what Dick was getting at is that the Polyphaser grounding lug needs to have its *own* ground - separate from any other ground. If you tie the Polyphaser to the electrical ground of the building, you're defeating the entire purpose of having it. But then again, I've been wrong before. <wink> Mark - N9WYS ________________________________________ From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of TGundo 2003 Sent: Friday, December 30, 2005 5:35 PM To: [email protected] Subject: Re: [Repeater-Builder] polyphaser Help Someone correct me if I'm wrong, but putting in your own ground rods and NOT tying them to the existing electrical ground system is a Bigger no-no. That would be creating a second ground system for the building and creating a potenital difference in grounds. That would be a bigger problem, and the local codes here require a bonding conductor of some sort. You can put in your own rods, which I agree with, but you must tie the two systems together and make it all one ground potential. It's all about equal potential, isn't it? If you don't get hit at all you don't have to worry about the voltages! How about the install on a all-steel mushroom type water tower? At the bottom the 1" threaded rods go in the ground and they are every foot around the perimeter. Makes a great ground plane for a DB-420! Someone please tell the cable guys to stop putting in the 4ft rods and creating ground loops! ;) Tom W9SRV Dick <[EMAIL PROTECTED]> wrote: Whatever you do, DON'T connect the polyphaser grounding lug to an AC outlet ground lug!!! That would bring HUGE voltages and currents into the building electric power system and expose everything on it to disaster!!! In which case you'd do well to carry enough insurance to replace all of the electric and electronic gear in the building. If you plan to connect it to the metal roof, make sure the metal roofing is securely grounded via an 8-foot ground rod in the earth near the building. In fact, there should be several such ground rods for a metal roof. The average frequency of a lightning discharge is around 125 KHz, so you can use that to calculate lightning rod cable lengths, etc. You might do well to contact the other tenants in the building and see how they feel about installing a proper lightning diversion system, including a proper lightning rod and cable. Happy New Year, Dick Yahoo! Groups Links Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
