Guy Olinger wrote:
Can you pass along your source of information that BL&E was done over 4
mS/m soil, ... Or are you using the FCC map for typical soil conductivities
and presuming a common New Jersey value and no variation at the site?
It is my presumption that for their cost and logistics, and with my 15 years
of insight as an RCA Broadcast field engineer (1965-1980), the BL&E
measurements were made near Princeton, NJ. I'll try to confirm that, and
advise. Princeton was the corporate facility containing the
office/laboratory of George H. Brown.
If those tests had been made at some physical location where earth
conductivity at/near the test site was significantly better than in New
Jersey, this would have been evident in their measured data.
For an example of this, if earth conductivity at/near the test site was 30
mS/m, then even relatively few/relatively short buried radials in contact
with that earth would enable higher radiated fields than shown in the BL&E
data for those radial numbers and lengths. This is illustrated by the NEC4
study using a short monopole on 1.85 MHz at this link:
http://i62.photobucket.com/albums/h85/rfry-100/10m_Vert32Buried_Radials.jpg
.
Even for an earth conductivity of 4 mS/m, the BL&E data show that monopoles
ranging from about 45 to at least 90 degrees in physical height, driven
against an r-f ground system consisting of at least 113 x 0.412-wave buried
radials, produces a groundwave field at 3/10 of a mile that is within
several percent of the maximum theoretical value possible for a perfect
monopole driven against a perfect ground plane, for that applied power.
The bottom line in all of this is that the worse the earth conductivity
within 1/2-wavelength of the base of a monopole (especially a short
monopole) while driving that monopole against a set of buried radials, the
more important it becomes to use a large number of such radials of lengths
approaching 1/2 of a free space wavelength.
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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