On May 11, 2005, at 10:35 AM, Jim Lux wrote:
> 4) Measuring phase on a scope to an accuracy of a few degrees is quite
> challenging. Spread one cycle out over 10 divisions, and each
> division is
> 36 degrees. By eye, you can probably estimate to a fifth or sixth
> of a
> division on a noisy signal. On a real clean signal, a tenth of a
> division
> is possible, so you're potentially in the 4-5 degree range,
> accuracy wise.
> With a good scope that has a X10 expansion, and with VERY stable
> triggering,
> you can do better, but you are really depending on the triggering.
>
> Don't forget that you're making a measurement between two signals,
> so the
> overall uncertainty is actually 1.4 times the uncertainty in
> measuring one
> signal.
Wouldn't it be easier to measure the phase difference by feeding one
signal to the horizontal amplifier and the other to the vertical and
measuring the angle of the resulting scope trace? In phase signals
should follow a 45 degree line, sloping low on left to high on right,
out of phase signals would present other angles.
You still have the same S/N problems, but measuring the angle should
be easy.
Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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