[mathcad] Re: DSP method

Author: Quang-Viet Nguyen Posted: Tue, 17 Jan 2006 09:40:34 -0500

At 10:09 AM 1/17/2006 +0000, you (Chris Whitford) wrote:
>The Nyquist frequency doesn't limit the accuracy of the phase measurement.
>This is determined more by the total length of the data, and how sharp the
>correlation is. You can interpolate to find the peak of the correlation,
>but this is only one sample from a distribution. If the same experiment
>were repeated multiple times, one would expect to find a scatter on this
>position. Depending on the quality of the data this scatter could more or
>less than the time step.

This is analogous to the use of a phase-sampled o-scope at limited
bandwidth to get higher accuracy phase-measurements on periodic signals by
averaging the signal. But it doesn't replace an o-scope with a higher
speed digitizer to capture a non-periodic (or single-shot transient) signal
- which will be Nyquist limited. If the data is periodic then longer
sample lengths permit a type of averaging which improves phase
resolution. For a cross-correlation on non-periodic data streams, does
having a longer sampling length improve phase resolution?

Quang-Viet Nguyen, Ph.D.

NASA Glenn Research Center
21000 Brookpark Rd, MS 5-10
Cleveland, Ohio 44135

Voice: (216) 433-3574
Fax: (216) 433-5802
E-Mail: "Quang-Viet.Nguyen" or "Quang-Viet.Nguyen-1"

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