In my post of yesterday, October 8 today I wrote:
But that is NOT the radiation pattern existing close to the monopole,
regardless of earth conductivity. That pattern has substantial radiation
at angles below 15 degrees. Such radiation will be shown when requesting
the surface wave in a NEC analysis, and specifying the distances in the
horizontal and vertical planes for the field values to be calculated.
In my post of yesterday, October 8, I wrote:
Now, if the relative field at 10 degrees elevation and 2-3 km H distance
from the monopole is 0.9 (which field is not an unrealistic value for real
earth), then unless the path on that vector is obstructed, there is no
reason in physics why that radiation will not continue on to reach the
ionosphere, and produce a significant skywave signal if propagation
conditions permit.
Please see the link below, in hopes that it will illustrate the points
above.
In this NEC analysis for 5 mS/m, dc 13 earth, the surface wave field at 2.8
km in the horizontal plane (16.2 mV/m) is 77% of the maximum field shown for
the far field (21 mV/m at 67 degrees elevation). The radiation toward 10.21
degrees elevation is 86% of the far field maximum.
Conclusions:
1) There are substantial fields _launched_ below 15 degrees in the elevation
pattern of a monopole, over real earth.
2) The field launched by a vertical monopole of 5/8WL and less over real
earth is NOT zero in the horizontal plane, as shown in a far-field
calculation.
3) The surface wave must be included for an accurate analysis of the
coverage capabilities of monopoles.
http://i62.photobucket.com/albums/h85/rfry-100/NEC_FF_with_Surf_Wv.jpg
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Remember the PreStew coming on October 20th. http://www.kkn.net/stew for more
info.
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