"The radiated field of a vertical monopole present on the surface of lossy earth decays at greater than a 1/R rate. But, for example, the field shown at a horizontal distance of 0.1 km in my surface wave plot for an elevation angle of 5 degrees is not located on the surface of the earth. It is about 9 meters above it, and in fact, is a space wave."
I'm not sure what plot you are referring to. Was this for a wavelength of something like 160m? 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. Based on the documentation I've found, the basic NEC model treats the radiated field as a combination of the direct (free-space) wave and the part reflected from the interface, for which it uses an approximation. I assume that any part of the solution not included in these two is called the surface wave. It does not, by definition, contribute to the radiated (i.e. 1/r) field. Am I misunderstanding their (and your) definition of the surface wave? -----Original Message----- From: Topband [mailto:[email protected]] On Behalf Of Richard Fry Sent: Friday, September 13, 2013 06:44 To: [email protected] Subject: Re: Topband: More anecdotal "stories" to cause one to stop and.... Jack WS3N wrote: >Then it would seem that what you call the surface wave must be the >remaining part of the complete solution, and so it must decay >exponentially in the vertical direction. ... a decaying solution can't >be projected in a straight line and assumed to reach the ionosphere. The radiated field of a vertical monopole present on the surface of lossy earth decays at greater than a 1/R rate. But, for example, the field shown at a horizontal distance of 0.1 km in my surface wave plot for an elevation angle of 5 degrees is not located on the surface of the earth. It is about 9 meters above it, and in fact, is a space wave. Space waves DO decay at a 1/R (non-exponential) rate until they reach the ionosphere. Here is a link to a clip from Radio Engineers' Handbook by F.E. Terman (1st Edition), showing that the greatest single-hop range for radiation from a 1/4-wave monopole leaves the monopole at elevation angles below 5 degrees. The reduction in skywave field intensity seen in this clip beyond 150 miles downrange is due to the 1/R losses of those longer paths. http://s20.postimg.org/g3yy1uust/Terman_Fig55.jpg _________________ Topband Reflector _________________ Topband Reflector
