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

[AJ4SQ]

"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:topband-bounces at contesting.com] On Behalf Of Richard
Fry
Sent: Friday, September 13, 2013 06:44
To: topband at contesting.com
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