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Richard Fry wrote:
AFAIK, neither NEC 2 nor NEC 4 from any source will show a composite elevation pattern over a defined ground at a specified distance to include the space wave and the surface wave in a single display. One must merge them using his/her own understanding and resources. Neither NEC-2 nor NEC-4 shows a display of any kind. Output is solely in the form of tables of numbers. Surface wave data, when produced, is always combined with the sky wave as a total field value. It's chosen with an option on the RP input "card". The NEC-2 manual as well as NEC-2 itself -- including source code which enables you to see exactly how the calculations are done -- are freely available on the Internet. So there's no need to speculate about what it does or doesn't do. EZNEC demo, standard, and plus program types don't include the surface wave in far field outputs, which as I explained in an earlier posting in another thread(*), isn't of much practical use to most amateurs. However, when needed the data can be obtained from the near field analysis (which is actually a total field analysis and isn't restricted to the near field). EZNEC pro program types (EZNEC-M and EZNEC/4) allow direct inclusion of the surface wave in the far field analysis, mostly for the use of AM broadcast consultant customers. It provides tabular and graphical outputs in the form of an azimuth plot at any desired horizontal distance from the antenna and height above ground. Like NEC, the output is the total field, or in other words the sum of surface and sky wave, and the results should be virtually identical to those from NEC. (*) I recommend that anyone interested in this topic read the posting I made just a few days ago, Sept. 28, on this newsgroup under the thread "Elevation Patterns of Ground Mounted Vertical Monopoles". It can easily be located at http://groups.google.com if it's not still on your newsreader client. Roy Lewallen, W7EL |
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