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## Re: [TowerTalk] elevated radials vertical

 To: "Al Williams" , Re: [TowerTalk] elevated radials vertical "Tom Rauch" Tom Rauch Fri, 8 Jun 2007 05:59:15 -0400
 > However the elevation pattern and gain using real ground > shows virtually no difference with 0,2,4, and 8 radials. > The source impedance jumps from highly reactive with no > radials to 50 ohms mostly resistive using two radials and > lowers a bit using 4 and 8 radials. > > The pattern and gain being nearly identical no matter how > many radials are use (including none) has me wondering if > I have something wrong in my model? Models don't do as well as people imagine for horizontal wires near ground. The model treats the earth like a big homogeneous mass with uniform characteristics. Now if the radials are high enough, say 1/4 to 1/2 wave above ground, things are OK. But when we put a wire very close to earth things fall apart. If your model is showing no difference between zero and four radials or showing four radials no different than 30 or 60 radials something is seriously wrong. You'll certainly make contacts with only two or four radials elevated radials, but more than half the power will be lost in the fields concentrated in the lossy earth near each radial. You'll also have a hard time decoupling the feedline from the antenna, so you'll have significant common mode currents on the feeder to deal with. None of this means the antenna won't work, and some people with vivid imaginations manage to convince themselves some very poor systems work well, but the fact is it won't be a good system unless you have ten or twenty radials minimum. And when you get the ten or twenty radials, they might as well be on the ground as elevated. The sole exception to this is ground that is a near- perfect insulator or a near-perfect conductor, or if the radials are a large distance in fractions of a wavelength above the lossy media. But even in those cases the feedline really needs decoupled because the antenna is neither perfectly balanced or perfectly unbalanced. 73 Tom _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk
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