Topband: More anecdotal "stories" to cause one to stop and....

[Richard Fry]

"AJ4SQ"  wrote:
>... I'm not sure what plot you are referring to.  Was this for a wavelength 
>of something like 160m?

Yes.

> I don't see how field values at a 100m (0.625 lambda) range and 9m 
> (0.05625 lambda) altitude can tell us anything about the far-field 
> behavior.

Note that such radiation may be relatively close to the radiator but is in 
its far-field, regardless of the terminology/convention used by NEC.  The 
near-field/far-field boundary is located at one radiansphere from the 
radiator, which is lambda/2pi (see clip below).  So at the 1.85 MHz 
frequency of my plots, that boundary is located at about 25.8 meters, and my 
calculations for 100 meters are about 3.88 times beyond that boundary, into 
the far field.

For background, I contacted Gerry Burke in January, 2012 when I was 
researching the basis for the comments I have been posting here.  Probably 
most will recognize Gerry Burke as the co-author of NEC software, working at 
Lawrence Livermore National Laboratory.

I sent him NEC surface wave plots similar to the one I posted in this 
thread, and asked him, "...would you expect the fields at elevation angles 
of 1 to 10 degrees in these plots to continue on to the ionosphere, and 
under the right conditions be reflected back to the earth as skywaves?

His reply was (quoted with his permission): "The low angle 1/R fields should 
reach the ionosphere, although perhaps not accurately predicted by NEC, 
since it does not include the effects of earth curvature and the 
ionosphere."

G. Burke's reply should be rather conclusive on the subject.

Clip taken from Kraus' ANTENNAS FOR ALL APPLICATIONS, 3rd Edition...

http://s20.postimg.org/xavzwzxwt/Kraus_Graphic_Fields.jpg