[Antennas] Ground Planes

Wed Apr 6 15:23:50 EDT 2005

Bill:
 Your modelling software may need some parameters. For elevated radials to be totally effective [read this to mean not affected or detuned by the ground], they need to be at least 1/2 wavelength about the ground on the frequency of use. On 40 meters, this would be 64 feet or so. Less than that and more radials would be required to acheive the same result and it would take considerably more radials than two within six inches of the ground. 
 Generally speaking, I would guess you would need to approach the 120 radials needed to ground mount a vertical if they were only 6 inches above the ground. In addition, the wavelength of the radials when mounted on or near the ground becomes less critical, except that longer is better than shorter for the same number of radials. Closer than 1/2 wavelength, the ground detunes the formual electrical length so that cutting them to a specific formula length doesn't really deliver what it implies. 
 Multiple radials of varying lengths would be best to enhance the conductivity of the ground return. Lastly, the ground conductivity will greatly vary the effectiveness described above and, as you know, conductivity varies greatly throughout the world. A lot of variables and a subject not easily explained.
Ron W7MRR
 --- On Tue 04/05, Dr. William J. Schmidt, II < bill at wjschmidt.com > wrote:
From: Dr. William J. Schmidt, II [mailto: bill at wjschmidt.com]
To: antennas at mailman.qth.net
Date: Tue, 5 Apr 2005 22:38:18 -0500
Subject: Re: [Antennas] Ground Planes
Interesting. I just modeled your system... two radials elevated six inches <br>off the ground on the diagonal is more effective than copper plating the <br>entire yard on 40-10 meters...<br><br>Sincerely,<br><br>Dr. William J. Schmidt, II K9HZ<br>Trustee of the North American QRO - Central Division Club - K9ZC<br><br>Email: bill at wjschmidt.com<br>WebPage: www.wjschmidt.com<br><br>"If computers get too powerful, we can organize them into a committee; that <br>will do them in." -- Bradley's Bromide<br><br><br>----- Original Message ----- <br>From: "Mel Vance" <icra at galaxynet.com><br>To: <antennas at mailman.qth.net><br>Sent: Tuesday, April 05, 2005 10:18 PM<br>Subject: Re: [Antennas] Ground Planes<br><br><br>>> of my test equipment when I hit 240 radials... and basis my threshold,<br>>> about 120 radials was really optimum given the cost of the wire.<br>>><br>>> Meshing your back yard... while it may give you wood... isn't really<br>>> cost practical.<br>>><br>> Radials are best...if you have 100 some feet dia to put them in.....<br>><br>> With a yard just 20 feet by about 100 feet, and cluttered with sheds, <br>> trees, ect, no way to<br>> jam 120 radials in there....hard to fit more than 10 into the yard <br>> available and clear trees,<br>> sheds, and other stuff<br>><br>> A mesh system should give a better ground than the hand full of radials I <br>> have room for.<br>> Also, my goal is not just for an antenna ground plane...due to very heavy <br>> clay, getting a<br>> good ground off a ground rod is very difficult. The mesh would get around <br>> that problem.<br>><br>> Mel<br>> N7OKL<br>><br>> ______________________________________________________________<br>> Antennas mailing list<br>> Home: http://mailman.qth.net/mailman/listinfo/antennas<br>> Help: http://mailman.qth.net/mmfaq.html<br>> Post: mailto:Antennas at mailman.qth.net<br>> <br><br><br>______________________________________________________________<br>Antennas mailing list<br>Home: http://mailman.qth.net/mailman/listinfo/antennas<br>Help: http://mailman.qth.net/mmfaq.html<br>Post: mailto:Antennas at mailman.qth.net<br>
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