Howdy, all -
Below is the text of a post I made recently on another website. Maybe some
here might find it interesting.
An accurate description of the radiation launched from a vertical monopole
needs to include the surface wave. To consider only the far-field pattern
generated by NEC or seen in antenna textbooks will lead to the conclusion
that the elevation pattern of a monopole over real earth of any conductivity
has zero field in the horizontal plane, and very little field at low
elevation angles above the horizontal plane.
The link below was prepared using values generated by 4nec2, but plotted in
other software. It shows that even NEC2 can be used to accurately calculate
low-angle fields radiated by a monopole over real earth -- and that the NEC
fields are very close to the accurately measured fields for those conditions
shown in the plot at the bottom of that page.
The NEC plot also shows that very significant space wave (skywave) is
generated by radiation from a monopole from elevation angles down to about
1 degree, where a NEC far-field plot shows very little relative field.
http://i62.photobucket.com/albums/h85/r ... ields2.jpg
Ham it up!
2 posts • Page 1 of 1
Interesting. As a side note I learned early on the hard way that when taking FI readings in a helicopter to do the vertical calibration at least a couple KM away from the antenna, otherwise all you're measuring is the vertical plane radiation pattern... ...and you end up somewhere on the left end of the green line on the graph and screw everything else up.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com