The FCC only suggests screens with voltage-fed antennas. The exact text is:
(4) At the present development of the art, it is considered that where a
vertical radiator is employed with its base on the ground, the ground system
should consist of buried radial wires at least one-fourth wave length long.
There should be as many of these radials evenly spaced as practicable and in
no event less than 90. (120 radials of 0.35 to 0.4 of a wave length in
length and spaced 3° is considered an excellent ground system and in case of
high base voltage, a base screen of suitable dimensions should be employed.)
Brown, Lewis, and Epstein's study of ground system efficiency for RCA (Radio
Corporation of America) didn't find anything especially beneficial using
screens.
I've used screens when I needed a wide bandwidth ground system, but never
under other conditions.
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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