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## Re: [TowerTalk] Chicken Wire Ground Screen

 To: towertalk@contesting.com Re: [TowerTalk] Chicken Wire Ground Screen Bill Tippett Tue, 16 Jun 2009 15:33:15 -0400 mailto:towertalk@contesting.com>
 ```K9YC: > It has long been well understood that return current is greatest near the base of the antenna, so copper near the tower is more important than copper at a distance in reducing I squared R losses. This is why AM broadcast stations often use a heavy copper screen that looks like monster chicken wire (40 ft x 40 ft is a number that comes to mind) in the immediate area of the tower, with radials terminated to the perimeter of the mesh. I believe this might be another broadcast myth (like supposedly needing 120 1/4 wl radials) and which is NOT mandated by the FCC. About 10 years ago I decided to make a ground screen for my 180' Topband vertical using ~16 50' X 4' rolls of welded galvanized fence wire (with rectangular openings about 2" x 4"...not the smaller gauge woven hexagonal chicken wire). I couldn't tell any significant difference in performance with this laid over my existing radial field (about 110 radials of 100-150') although I didn't actually make before and after measurements. I later read an edition of ON4UN's book which indicated you could achieve a nearly perfect near-field ground using 1/4 wl radials spaced ~.025 wl apart at the tips. Doing the math for 160 this implies ~13 feet apart at the tips. No matter how long your radials (even if differing lengths), you simply maintain the 13' spacing at their tips for an optimum ground. For 1/4 wl radials, this implies 60 (radial circumference / .025 wl spacing = 60 radials). For longer radials, it implies more. If you accept this logic (which I do because several including W8JI, N6LF and others point to ~60 as an optimal number of 1/4 wl radials), then there's little point in a ground screen near the antenna. Assuming the approximate dimensions of a ~40' square ground screen (I'll assume a circular radius of 20'), your 60 radials above are only 2' apart (0.004 wl) at 20' out, so the improvement from a ground screen should be minimal. Of course the radial spacing becomes even closer as you near the base. My galvanized fence wire has long since rusted out and quite frankly I now wish I had never put it down because it's now a hazard to trip over. If anyone is serious about ground screens I believe you are well advised to use real copper which will last forever (but I hate to think what that might cost). IMHO you are better advised to forget any sort of ground screen and spend your money on at least 60 1/4 wl copper radials which will last forever. 73, Bill W4ZV _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
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