Topband: Modeling "Ground"

[Jim Brown]

On Sun,2/22/2015 4:40 PM, Guy Olinger K2AV wrote:
> Ground, as it affects numerous wire on/in/around ground situations, is
> poorly understood, and there is no Daddy Warbucks out there willing to pay
> the bill for the research it would take to fill in those blanks.

I agree with W8JI and others who have observed that the earth's surface 
layer (what we call "ground" in a modeling context), is quite complex, 
and far from uniform. There's also the matter skin depth, the 
contribution of moisture, chemical composition, and so on. As I view it, 
there may be nothing at all wrong with the math -- we've had math 
figured out quite well for several centuries -- but rather with KNOWING 
enough about that surface layer we call "ground" to write the equations, 
and the complexity of the "ground" that makes those equations impossibly 
complex.

And even if we could know enough to write the equations or plug numbers 
into them, how many Crays would it take to compute the model?  :)

In my professional life as a designer of sound systems for large 
acoustic spaces (theaters, churches, stadiums, arenas), I often built 
rather sophisticated and detailed 3D models of these spaces that 
included the reflection characteristics of hundreds of different surface 
materials, inserted 3D models of loudspeakers generated by measurements 
of the performance characteristics in octave bands (later in one-third 
octave bands), then had the software compute the response of the system 
(the loudspeaker and the room) at hundreds of points over the audience 
area, used the computed result to predict speech intelligibility, and 
convolved a .wav sound file (usually speech, but it could be music) with 
a .wav file describing the system response to produce a new .wav file 
that we could listen to that predicts what the system would actually 
SOUND like.

This acoustic modeling software started out life in the early 80s in 
what was then East Berlin, and ran on PCs of those days. It was far 
simpler then, only modeling the direct sound on the audience. 
Development was, and still is, ongoing, and every five or so years, new 
versions allowed more and more complex calculations, more data for 
surfaces and loudspeakers have been made available, computers that can 
we can buy and put on our desk become more and more powerful, and with 
more storage.

I suspect that somewhere, someone (or many someones) are working on 
modeling software of comparable complexity to that acoustic software -- 
indeed, K6OIK has listed several professional packages of considerably 
greater capability and complexity as compared to the NEC engines. Here's 
a presentation he did in 2008 at Pacificon. I've heard him do a newer 
version, but I can't find it on the internet.

http://archive.k6ya.org/docs/Antenna-Modeling-for-Radio-Amateurs.pdf

73, Jim K9YC