[time-nuts] ADEV measurement question
Tom Van Baak
tvb at LeapSecond.com
Sun Aug 23 13:19:40 EDT 2015
> To learn more, I think the best way would be to put the
> counter into its fast binary mode and acquire 1k time
> interval samples per second. That would give me loads of
> data to play with and it would be easy to try out how
> different averaging schemes affect the result.
See: http://leapsecond.com/pages/adev-avg/ for the results of a similar ADEV averaging experiment. I can send you the raw data if you want.
What helped me understand the issue was to think in terms of frequency *in*stability instead of frequency stability. We often use the words interchangeably. But imagine that your goal is to measure oscillator noise, its instability, not its stability. With this new mental image the last thing you would do is average. By its very nature, averaging removes highs and lows and smoothes things out. If your goal is to measure instability, averaging removes the very thing you're trying to measure.
The plots in the above web page show this dramatically. You can make an oscillator as good as you want if you average enough.
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