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## [TowerTalk] vertical antennas

 To: [TowerTalk] vertical antennas W8JI@contesting.com (Tom Rauch) Tue, 23 Oct 2001 20:41:18 -0400
 ```> Even in this area I have found some different ideas. Mainly, their is > one train of thought that ground radials need not be longer than the > height of the vertical radiator (in my case, 60 ft.). The other > train, always use quarter wave radials (130 ft) regardless. That is an unfounded old Ham's tale, just like the idea that two or four elevated radials is enough. (Four radials are enough if they are a hundred feet or more above ground on 160). This was all measured out many years ago in a study commissioned by RCA. Prior to the study virtually all ground systems were sparse resonant counterpoise systems. The study drove a stake through that idea. Now some have taken a step backwards and claimed the opposite, but every case I have seen where a system was compared (I did two separate tests as well as measured one BC station) with ONLY a radial change there was 3 to 6 dB advantage using a conventional large ground system. Shorter verticals actually require larger (and that means longer) ground systems, because the current is much higher. You need long dense radial fields to have a low ground resistance. As the vertical is made taller, the ground system becomes less critical. The general rule is that when the largest wire spacing is about .025 wavelength, the wires "look like" a solid sheet. Adding more wires does not good at that point. 1/4 wl long is normally long enough in any situation on 160 meters. That would mean the open end of the radials should be about 14 feet apart so you'd need about 50 or 60 1/4 wl radials to reach the knee of the efficiency curve if the radials were all evenly spaced. What I do, in areas where I can't run a full 1/4 wl, is move a 14 foot rope along to mark the perimeter. I wind up with more radials where the radials are longer. > I wonder what the "thread" is on this. In my situation, I can lay 130 > ft radials for 270 degrees. In the other 90, radials are going to > decrease in length to about 60 ft for the shortest (perpendicular to > the property line). Is this going to noticable affect the performance. The effect would almost certainly be nothing you would notice, as long as you go by the .025 wl maximum spacing rule. 73, Tom W8JI W8JI@contesting.com List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems, Trylon Titan towers, coax, hardline and more. Also check out our self supporting towers up to 100 feet for under \$1500!! http://www.anwireless.com ----- FAQ on WWW: http://www.contesting.com/FAQ/towertalk Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com ```
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