|Subject:||Re: [TowerTalk] Ground Radials Insulated or Not|
|From:||Jim Lux <firstname.lastname@example.org>|
|Date:||Mon, 06 Dec 2004 13:56:49 -0800|
At 01:46 PM 12/6/2004 -0500, Gary Schafer wrote:|
Jim Lux wrote:At 08:18 AM 12/6/2004 -0800, Michael Tope wrote:
You can't necessarily, but it's more that the design requirements for each are different. I don't say it's practical or desirable, but one could imagine a narrow band filter at the feedpoint (connected beween vertical element and ground field) that passes only the desired amateur band.
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.
But is a good RF radial grounding system really "one of the best lightning grounds you can get". A raft of small wires might well be a worse lightning ground than a few nice big wires or rods. The smaller wires may fuse with the lightning current. Say you get a 20kA strike and you've put in 60 wires. That's 300+ amps into each wire (if the current divides equally, which it probably won't). 300 Amps is a ballpark fusing current for AWG10 wire in air (admittedly, that doesn't take into account the short duration of the lightning impulse, etc.)
However it would not hurt to install a few ground rods connected to the radials in addition.
I'll say that this is true. For just the reason described above.
What's standard practice in the broadcast industry?
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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