[time-nuts] Update on Rb Performance

[ws at Yahoo]

John

If you have the raw phase data, can you post a plot of what the well 
filtered freq offset looks like over that 10 day period?
I've have found a properly filtered high resolution freq vs. time plot 
provides a lot more useful information than the couple of data numbers of a 
ADEV plot for evaluating long term performance of an Osc and helps separate 
all the many different possible causes of  poor ADEV numbers.
This is because then one can see the shape and magnitude of the Freq drift, 
therefore being able to see if the freq drift has a short term cycle due to 
temperature or if it is linear due to ageing or 2nd order due to still 
stabilizing or if it contains freq jumps due to 1/f flicker, or a single 
large jump due ...etc,  etc.
To be of any long term use, the freq data must be filtered over a long 
enough time period, such as a 1 hr running averaged, so the plot is more 
than just the 1 sec noise shown on most freq plots.
The big avantage of using long term freq plot instead of a ADEV plot is the 
freq error is not noise but sytimatic errors which I have found to generally 
be the casse over longer time periods, then 10days worth of data can be use 
to prdict the what the future performance will be, compart that to what 
10days of ADEV give, a lot of uncetaiy to even prdict what the one day drift 
will ber.if the Noise is not noise but due to Using a 10 day
ws
****************

John Ackermann N8UR jra at febo.com

This isn't the real long-term stability test I'm planning to do, but I
did let the measurement continue on the last unit I was testing (an
Efratrom FRS-type) out to 10+ days, which should give fairly reasonable
data out to 100K seconds.  An ADEV plot is attached.  I would ignore the
last two plot points as there isn't enough data for them to be very
meaningful.

Bottom line is that Efratom specs the FRS units at <1e-10/day, and this
one seems to do more than an order of magnitude better.  But also looks
like you need a lot more than 10 days data to draw any real conclusions;
you can look at this plot and think that the ADEV is maybe heading back
down after a peak near 1e-11.

John