I have recently completed a series of tests comparing the signal strength
between a 40m vertical with 32, 1/4-wave, radials in a complete circle to
the same vertical with a sector missing from the radial system. This
represents the case of placing a vertical near an obstruction such as a
building. Even over my rather good soil the results are discouraging.
There is signal reduction in all directions but the greatest reduction is
towards the missing sector. I observed from 0.5 to over 3 dB of signal loss
in various directions. Over poor soils these numbers would be even worse.
This does not take into account the loss due to a building in immediate
proximity to the vertical which is not likely to have a positive impact.
NEC modeling gives similar results to my experiments, overall signal
strength is down and the pattern is distorted.
These results will be published in the Nov/Dec 2009 issue of QEX magazine.
In the meantime I suggest that placing a vertical against a building is
probably a bad idea. If you have any other option, take it.
73, Rudy N6LF
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