I'm in total agreement with Tom's comments, based on first hand experience for
the last two years after replacing my old elevated
radials.
I had a good 160 meter 4-square vertical array for years, with two
elevated radials on each vertical. Two years ago -- after tiring of
consistently playing second fiddle to the DXers with good radial systems -- I
installed sixty 120 foot radials on each of the four
verticals. The difference in performance has been truely awesome. My
first QSO with the new array was UA0, zone 18, in a small pileup with
only VE1ZZ, and the UA0 heard me first! I knew right then and there
that I had a winner on my hands. 100 countries worked in a single
weekend, in the 2006 CQ WW CW DX Contest, was a feat I'm absolutely
certain we could not have achieved with the old elevated radials.
I should have listened to Tom's good advice years ago. He's right,
listen to him!
73
Frank
W3LPL
---- Original message ----
>Date: Fri, 8 Jun 2007 05:59:15 -0400
>From: "Tom Rauch" <w8ji@contesting.com>
>Subject: Re: [TowerTalk] elevated radials vertical
>To: "Al Williams" <alwilliams@olywa.net>, <towertalk@contesting.com>
>Cc: Rich Patrick <rfpatrick@yahoo.com>
>
>> 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
>
>
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