With reference to the quote below from the interesting paper titled "The
Brown Paper and Conclusions with a Ham Focus - N6MW March 25, 2015, linked
in the OP of this thread title:
\\ The field strengths are always compared with that expected for the same
antenna height but over a perfectly conducting infinite plane - this
comparison is remarkably (some might say something stronger) close for
many/long radials. //
Just to note that it is quite predictable for the fields measured in the
BL&E experiments when using many/long buried radials to be nearly equal to
those when using a perfect ground plane. BL&E Fig. 38 (link below) shows
the reason for this.
The measured resistance R shown in Fig. 38 for 113 x 0.412-lambda radial
wires is virtually identical to the theoretical radiation resistance of the
77-degree monopole used for that test. IOW, the r-f loss of the radial
ground system is close to zero for those conditions, even given the fairly
poor earth conductivity at this New Jersey test site.
Therefore if the ground plane and radiator both were perfect conductors,
then by published equations the groundwave field produced at a radius of 1
mile by 1,000 watts of applied power will be about 194 mV/m as shown in the
BL&E charts.
BL&E Fig. 38 shows a field of about 190 mV/m at 1 mile for 1000 watts and a
77-degree radiator used with 113 x 0.412-lambda buried radials, which is
about 0.18 dB below that produced by a perfect system of that configuration.
This small difference in fields could be expected, due mostly to groundwave
propagation loss across the short, 0.3-mile path over real (lossy) earth
from the base of the monopole to the location of the BL&E field intensity
measurement.
http://s17.postimg.org/agcdab9jz/BL_E_Figs_38_39.jpg
R. Fry
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|
