Path: utzoo!censor!geac!torsqnt!hybrid!scifi!bywater!uunet!optilink!elliott From: elliott@optilink.UUCP (Paul Elliott x225) Newsgroups: sci.electronics Subject: Re: Ground Plane for my CB antenna Summary: any length in excess of 1/4 wave (radials) will *not* work Message-ID: <5235@optilink.UUCP> Date: 11 Jan 91 18:16:27 GMT References: <17660140@hpfcdj.HP.COM> Organization: Optilink Corporation, Petaluma, CA Lines: 29 In article <17660140@hpfcdj.HP.COM>, myers@hpfcdj.HP.COM (Bob Myers) writes: > A quarter-wave vertical antenna works just fine against > an *infinite* ground plane, if said plane is flat and orthogonal to the > radiating element. So any length in excess of 1/4 wavelength should work, > and we see that ground-mounted verticals require no radials whatsoever, > assuming that the local ground (in the sense of the earth itself) is good > enough. [ as the radial "droop" angle goes from 90 deg to 0 deg...] > Obviously, it damn well better be 1/4-wave when you get to zero and the > thing becomes a vertical dipole! Wait! The 0-degree case (horizontal radials) does indeed require 1/4-wave radials. The object is for the radials to present a zero impedance at the center, thus simulating a good artificial ground. The 1/4-wave case uses the impedance transformation property to convert the open-circuit at the end of the radial to a short-circuit at the center. Making the radials arbitrarily longer than 1/4 wave just doesn't cut it. The reason that untuned radials can be used for ground-mounted verticals is that they are used to couple into the true ground (so to speak). -Paul wb6cxc -- Paul M. Elliott Optilink Corporation (707) 795-9444 {uunet, pyramid, pixar, tekbspa}!optilink!elliott "If I had known it was harmless I would have killed it myself." - P.K. Dick