precision_timing:allan_variance_challenges_and_opportunities [KO4BB Wiki]

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+====== Allan Variance, Challenges and Opportunities ======
+{{:precision_timing:symmetricom_-_allan_variance_-_challenges_and_opportunities.pdf|}}
+The attached white paper from Symmetricom may be of interest.
+Among other things it explains why a common technique is largely a waste of time for tau greater than the inverse PLL bandwidth.
+It also indicates that using a bandpass filter centered on the beat frequency really should be used in DMTD systems.
+However the associated filter phase shift tempco will require that the filter components have low tempcos and will require elaborate temperature control if analog filters are used.
+The best compromise would be to use a high end sound card and use digital filters.
+One can then interpolate to accurately time stamp the zero crossings of the bandpass filter signals.
+Although this method doesn't make optimum use of the signal samples it will implement a more ideal DMTD albeit with a noise level of around 1E-13/Tau.
+However, one is still left with the problem of calibrating the sampling clock.
+Bruce