Topband: Skywaves from Monopole Surface Waves

[Richard Fry]

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