|To:||"Michael Tope" <W4EF@dellroy.com>, "Chuck" <email@example.com>|
|Subject:||Re: [TowerTalk] Ground Radials Insulated or Not|
|From:||Jim Lux <firstname.lastname@example.org>|
|Date:||Mon, 06 Dec 2004 09:50:41 -0800|
At 08:18 AM 12/6/2004 -0800, Michael Tope wrote:
From a performance point of view, I suspect it doesn't make any difference at all whether the wires are insulated or not. One consideration that I haven't heard discussed with regard to radials, however, is lightning protection. Wouldn't it be better from a lightning perspective to have at least some of the radials in the system uninsulated? Perhaps a few heavy radials (6 to 8) made from #4 bare copper interspersed with the balance of the radial system made from whatever is cheapest. Just a thought.
One might argue that you want to keep the "RF grounding" function of the antenna (which, after all, is connected to the coax shield) separate from the "lightning current discharge" function.
The junction from antenna/tower/whathaveyou to the lightning ground is going to rise in voltage pretty substantially, regardless of how good the ground is. A notional 5 ohm ground with 10kA lightning stroke current is going to go to 50 kV.
I'll have to look for the details, but I seem to recall that one of the analyses that NEC-4/NEC-3 were designed for was to look at whether lightning grounds should be combined with RF grounds (particularly radial fields). I do recall that they came up with the surprising finding that with elevated radials, the performance with the radial field connected to the ground stake was worse than with them separate.
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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