On 5/13/11 9:26 AM, Jim Brown wrote:
and 2) interaction of the wavefront
> with the very dense redwood forest surrounding the antennas (how ya
> gonna model that?) .
I've had moderate success (maybe) with modeling the trees as lossy
conductors (big fat wires) in NEC4
The real problem is that there is precious little published data on the
RF properties of forests at HF frequencies. There's some "bulk loss"
stuff collected in the 60s (Vietnam War era).
But fooling with a model of fat lossy wires, I've managed to duplicate
some of the data in the papers. (but with a healthy dose of empiricism
to fiddle with the "resistivity" of those wires.. but at least, once I
find a number that works with one case, the rest of the cases in the
paper seem to match within 30-50%)
I've also contemplated the same approach to modeling the effect of a
house (e.g. you want to model a wire antenna on a typical suburban lot
with a house in the middle of the lot).
Again, precious little published data to validate against, so mostly
what I do is "sensitivity analysis"... Run the model multiple times
varying the parameters for the "house model" and see if it makes any
significant difference in the antenna system performance.
If it doesn't then I figure the house doesn't affect anything.
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