[time-nuts] GPS: ADEV or MDEV?

Poul-Henning Kamp phk at phk.freebsd.dk
Tue Apr 10 01:25:56 EDT 2007

In message <004e01c77b09$d095aa60$6500a8c0 at EBS8500>, "Brooks Shera" writes:

>The impact of time averaging  to suppress white phase noise is illustrated
>by a new plot TVB has created and placed on his website
> http://www.leapsecond.com/pages/3gps/gps-adev.gif.
>These revealing plots show that just a few hundred-second time average has 
>largely removed the performance
>difference between the aged VP and the newer M12+ and has almost entirely
>removed the benefit of sawtooth correction (CNS-CNS II).  These important
>results are not evident in the usual ADEV plot.

This is simply not true.  No averaging period can ever guarantee you
will not get a constant offset from the sawtooth.  You may get rid
of the noise, but not the bias.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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