[time-nuts] Some long-term data

[John Ackermann N8UR]

Tom Clark, K3IO said the following on 12/24/2006 12:26 AM:

>    The straight ADEV will certainly be affected if there is a drift. The
>    ADEV for delta time=T is simply the RMS difference between the clock
>    phase at time t and time t+T. Any rate offset will appear in this
>    calculation.

I must have been mistaken then, because I recalled (probably
incorrectly) some conversation here that a linear drift would not have a
significant impact on the calcluation.

>    If you are using STABLE32, you might want to fit out a smooth
>    polynomial with the tools that are supplied. Or as an alternative, use
>    the Modified ADEV; this computes the difference to both earlier and
>    later times and implicitly includes the removal of a simple offset.

I will play a bit more with the different versions of ADEV.

>    John -- you can get info on STABLE32 at [1]http://www.wriley.com/.
>    Even if you don't get the software, the manual is a good bible and can
>    be fetched at [2]http://www.wriley.com/Manual146.pdf. Pay special
>    attention in the manual to pages 31-49 for a discussion of the types
>    of variances that are of use in the community. FYI -- The folks who
>    maintain the Rb and Cs clocks on the GPS satellites are sold on the
>    Hadamard variance as a long-term performance measure.
>    To learn how to read an interpret the slopes on an ADEV plot, refer to
>    pages 77-83. On page 79, you will see that the Modified ADEV gives you
>    more information in the short-term (i.e. the area where the VCXO is
>    the principal contributor) part of the curve for White vs Flicker
>    phase modulation.
>    I highly recommend STABLE32 -- many of us have found it well worth the
>    $400 price that Bill Riley charges for his labor of love!
>    73, Tom

Yeah, Stable32 really is excellent, and the manual has lots of good
stuff that I need to study more!

Thanks!

73,
John