> 6) Keeping track of the length of the antenna element is a little
> problematic. Stepper motors can lose calibration. For a dipole, an
> SWR bridge could be used for final adjustments to the length. A yagi
> would require more accuracy. You might use an optical encoder on the
> spool, or even one of these cheap optical mice for computers. The chip
> they use has outputs for that which would make this easy, but I have no
> idea how they would respond in a high RF environment.
Actually, in a stepper motor driven system, you only need to sense one
absolute position and let the stepper motor do the relative positioning.
Its an age old trick in automation. On power-up, you have the stepper go in
a particular direction until you find the home position and then just keep
track of the steps from then on. (That what that groaning noise is from
your old floppy disk drive when you turn on your computer.) So that means
you just need one hole in the BeCU strip, or just use the end of it.
Naturally, the disadvantage is that you have to wait for the system to
calibrate itself when you first turn it on, but some people might not
consider that a real hardship. If I were marketing the antenna, I would do
it the SteppIR way, but if it were my homebrew antenna, I would be happy
with the startup calibration idea.
Dudley Chapman - WA1X
_______________________________________________
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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