At 12:50 PM 10/18/2005, Jim Brown wrote:
>On Tue, 18 Oct 2005 10:03:41 -0700, Jim Lux wrote:
>
> >How accurately do you need the numbers? (10% good enough, or do you need
> >sub 1% accuracy?)
>
>Sub 1% accuracy? Are we talking real world or fignewtons of someone's
>overactive imagination? Stray effects in real antennas, especially those
>built and installed with finite budgets, are going to skew their behavior
>for a lot more than 1%. Among the variables are the nature, proximity, and
>slope of the earth below the antenna, the nature and geometry of
>surrounding objects, and the geometry and characteristics of the elements
>of the antenna itself.
>
>Jim Brown K9YC
There ARE people who want to calculate/model inductance to 1 part per
thousand. For filter applications, inductors are designed to those sorts
of tolerances (that is, holding 0.001" tolerances on a 1" part isn't
impractical).
I agree that for "real" HF antenna components, such over precise
calculations may be less than useful, although just in the last few days,
folks were talking about the differences in resonant lengths for dipoles in
the sub 1% tolerance range. And, for microwave antennas, holding
tolerances of 1/20th of a wavelength at 32 GHz over a span of 3 meters is
regularly done. That's about 1 part in 10,000.
The program from Brian, K6STI, displays inductance and resistance to 0.001
uH precision (not that it's meaningful) It also displays distributed
capacitance to 0.01 pF.
I have no idea what algorithms Brian used to calculate wire loss or form
loss or distributed capacitance. There are well known algorithms from
Grover, Medhurst, and Wheeler for this kind of thing, and they are
potentially accurate to better than a percent, and maybe, a bit better.
The next step is usually some form of finite element model. NEC is a good
FEM modeler for structures that are composed of conductive wires, but not
that hot for for very small features, nor for structures where dielectrics
play a big part.
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