On 9/11/2011 11:46 AM, Charles Moizeau wrote:
> I do find it quite extraordinary that within the first 50 feet of radius of
> your larger plot of 60 radials that extended variously to lengthsof 60-135
> feet, you were able to achieve a significant performance increase by adding
> four 50-foot lengths of four-foot wide rabbit screening (2" x 4").
I don't recall from the original post how much improvement was noted,
but it is generally well known that current distribution in the ground
system as a function of distance from the feedpoint roughly approximates
current distribution in the antenna itself. Thus, for an antenna that
has a current max at or near the feedpoint, reducing the impedance near
the feedpoint would reduce the loss more than reducing the impedance at
much greater distance. This is quite well known. Now, with the radial
system described, I wouldn't expect to see much more improvement than a
dB or so from adding the mesh unless the radial system was in bad shape.
Another point -- in AM broadcast stations, where a robust copper mesh is
usually employed for some distance surrounding the tower, radials are
bonded to the perimeter of the mesh, NOT to the feedpoint. Of course,
this mesh is heavy gauge copper, not chicken wire. :)
73, Jim Brown K9YC
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