[time-nuts] question Alan deviation measured with Timelab and counters

John Miles john at miles.io
Mon Jan 19 19:55:48 EST 2015

> John,
> Your new three-corner hat feature is really cool. Already tried it, even
> if I did not spend quality time on setting source labels correctly.
> Whenever I have a setup capable of running it, I will test-spin it again.
> I suspect that when you make separate measurements, the noise of the
> individual sources does not match up perfectly which may reduce quality,
> especially systematics like hum.

True, and Bill Riley's documents emphasize that simultaneous measurements are best.  That's easy to do with the SMA jacks on the TimePod but more of a challenge with counters, unless you buy several of them and run them from separate GPIB adapters or serial dongles.  

IMO, if you can keep correlation, tonal artifacts, and other systematic errors under control and make long-enough measurements to generate a lot of data points in the tau range of interest, then the technique should work well with non-simultaneous acquisitions.  At the end of the day it's no better or worse than the quality of the individual ADEV measurements.  You have to be wary of measurements at taus where any of the traces have large error bars or are wandering up and down over time, or where some of the traces are suspiciously close to each other.

-- john, KE5FX
Miles Design LLC

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