For most of the past century the intractability of the equations was the
excuse for just laying down "textbook" overkill radial systems. If you
can't solve the "real world problem", then just change the real world to
match the problem you can solve!!! (Google "spherical cow").
Today I think the variable moisture depending on weather, and poor
measurement of soil RF properties is the limit to tractability of
computations. It doesn't matter how good your equations or computers are if
you are not using the right material properties. Garbage in, garbage out.
The folks who do ground penetrating radar make very good measurements and
some go as low as 10MHz. Still when comparing cost of massive copper
systems to cost of making ground penetrating radar measurements in a
variety of weather conditions, I suspect massive radial systems will still
win.
Tim N3QE
On Sun, Feb 22, 2015 at 8:18 PM, Jim Brown <jim@audiosystemsgroup.com>
wrote:
> 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
>
>
>
>
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