Hi Clive,
If this is your 40 meter antenna, it is already working pretty
well.
I'm assuming (since you didn't specify) that you are talking
about the radial field surrounding the base of a full size or
near full size 1/4 wavelength _vertical_ radiator. I'm also
assuming that you are talking about radials which are on the
earth's surface or just below it. In that case (we're already
two assumptions down at this point), the screen density you
describe is sufficient for a radial length of only about 1/4
wavelength (thus generating a third assumption by inference).
Depending mostly on the initial state of the local ground
conditions and radial system (also unspecified), improving one
half of a radial field with a radius of 1/4 wavelength may or may
not get you a few dB of improved efficiency. But any improvement
will apply nearly equally to all parts of the pattern. There
will be a small effect on the TOA and total energy in the pattern
in the direction of the improved ground. But the difference
(compared to other directions) will be largely insignificant. To
really do TOA lowering by improving the ground around a full size
vertical, the ground must be improved for a great distance out (3
to 8 wavelengths depending on your goals). The required radial
density for 3 wavelength long radials is much higher than for 1/4
wavelength radials. For example, a 3 wavelength radius radial
field with a screen density at its outer edge equivalent to a 1/4
wavelength radius field with 120 radials would require
approximately 1260 radials.
I normally apply a "relevance loss" of 3 dB per assumption to the
information transferred as it relates to the specific instance
actually being discussed. So you should bear in mind that this
may only apply to your installation to within about -9 dB. ;-)...
Or it might be dead on - IF the assumptions were OK.
73, Eric N7CL
>From: "Clive Penna" <clive@gm3poi.prestel.co.uk>
To: <towertalk@contesting.com>
>Date: Sat, 27 Mar 1999 11:42:26 -0000
>
>HI, Does anyone have any field strength data, re the lowering of
>radiation angle in a given direction if extra radials are
>concentrated in that direction. ie taken to the extreme 60
>radials covering 180deg whether that arrangement would have the
>performance of 120 radials at the mid way point,and the
>radiation angle increasing as you run out of radials. 73 Clive
>GM3POI
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