Conclusions from graphics of the Brown, Lewis & Epstein ground systems
experiments (linked below)...
- When relatively few buried radials are used, there is little improvement
in the GW E-field radiated by monopoles with a physical height of 77 degrees
or longer when those radials exceed about 50 degrees in length (a free-space
physical length of 0.137 lambda).
- The greatest GW field at 0.3 miles downrange radiated when using 15 x
0.412-lambda buried radials is about 1.9 dB below the theoretical value for
a perfect monopole of that height driven against a perfect ground plane
(other things equal).
- When 113 (or more) radials of 0.412 lambda are used, the greatest radiated
field is about 0.22 dB below the theoretical value. This corresponds to an
increase in radiated power of about 47% compared to using only 15 radials of
0.412 lambda.
- The field when using 15 radials of 0.137 lambda each is within 0.3 dB of
that when using 113 radials of 0.137 lambda each (other things equal). The
increase in radiated power when using 113 rather than 15 radials of 0.137
lambda has dropped to about 7%.
These field improvements also affect spacewave/skywave radiation, as the
improvements are based on the power radiated (launched) by a vertical
monopole at all elevation angles below the zenith. Therefore these findings
have value for ham radio operators, even though hams usually are not too
concerned about groundwave radiation.
Here is a relevant quote from pp. 773-774 of the BL&E paper (the 45 foot
radial length corresponds to 0.137 lambda at the 3 MHz test frequency):
\\ When the radial wires were 45 feet long, the measured resistance was
practically independent of the number of wires. Evidently, most of the earth
loss occurred in regions beyond the periphery of the ground system. //
http://s17.postimg.org/agcdab9jz/BL_E_Figs_38_39.jpg
R. Fry, CPBE
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