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Title: Monopole Radiation Patterns w.r.t. Earth Conductivity Post by: R. Fry SWL on October 23, 2012, 07:21:51 AM For comment/discussion... AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Other things equal, the field values in the vertical plane radiation pattern first "launched" by a monopole are a function of earth conductivity. But the shape of the radiation pattern close to the monopole remains essentially the same for all conductivities, as shown in the link below. The fields in the NEC4 analysis below were calculated along a vertical distance of 0-50 meters above the surface of the earth, at a horizontal distance of 100 meters from the monopole. A vertical distance of 50 meters for this chart is an elevation angle of 26.6 degrees from the monopole. Note in the chart that the radiated fields at elevation angles below 26.6 degrees are greater than the field at 26.6 degrees. For the lowest elevation angles, those fields are FAR greater than those shown in a NEC "far-field" analysis, which for real earth go to zero field in the horizontal plane. At an elevation distance in the chart of 15 meters (8.5 degrees), the difference in the field shown for 1 mS/m conductivity and that for sea water conductivity is 2.6 dB -- probably less than intuition would expect. It is the low-angle radiation directed toward the ionosphere from the fields at ~this electrical distance from the monopole that can produce useful skywaves having the greatest single-hop range. http://i62.photobucket.com/albums/h85/rfry-100/Monopole_Surf_Wv_Compare.jpg |