More on modeling SteppIRs:
I'm also curious about how one would go about modeling the algorithm in the
SteppIR controller... Does one set up a 3 el yagi model, and run an
optimizer to adjust the lengths to achieve some goal, assuming that this is
what's canned into the controller?
I'd think that SteppIR optimized for F/B, since that varies much faster than
something like forward gain. Small changes in element currents can trash a
20dB null without too much trouble, but that same small change is a sub
tenth dB variation in gain or directivity.
Actually, what's inside the box is an interesting question (and I wouldn't
expect SteppIR to be forthcoming, for a lot of reasons, all pretty good
ones). However, it does bring up the interesting "how do you effectively
model" question. For instance, QST has that policy about advertising gain
numbers, which must be substantiated by a model or range measurements.
Setting up a calibrated and validated range for HF antennas is no trivial
matter, so it makes reviewing the performance of such devices in an
objective way difficult. (you get into those horrible debates based on
working obscure countries on microwatts of power:.. I worked 4000 countries
on a piece of special pasta my great grandmother made, and she's is a direct
lineal descendent of both Guglielmo and Nikola, so clearly she's hot stuff
in antenna design).
At least for more conventional antenna designs, you can go out and measure
the aluminum and build a model that will be reasonably accurate, at least
when compared to models of other antennas of similar design.
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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