[time-nuts] Some long-term data

[Tom Clark, K3IO]

   As a comment on this dialogue:

> > Such as temperature and humidity. One of the Cesiums seemed to have a rathe
r
> > large frequency offset. Did you drift-compensate your ADEV measures or not?
      

> 
> No, I ran the ADEV in Stable32 without removing drift.  My understanding
> is that linear drift shouldn't affect the calculation.  I was also a
> little concerned whether drift removal would work very well given that
> both Cesiums had periods where the offset changed for quite a long
> period (CS1 near the end of the data, CS2 at the beginning) and I wasn't
> sure what impact that might have.
    

  

   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.
   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.
   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

References

   1. http://www.wriley.com/
   2. http://www.wriley.com/Manual146.pdf