[time-nuts] Sapphire instead of Quartz for much better Phase Noisespecs

Tom Van Baak tvb at leapsecond.com
Fri Nov 26 15:30:48 EST 2004

> But it appears that they are used as phase locked
> microwave frequency sources rather than free running
> oscillators.  But phase noise should translate into
> good Allan variance and so they should also be good
> when free running.

True, phase noise is related to Allan variance. But phase
noise has nothing to do with long-term stability. Think of
long-term stability as ADEV for tau in the range of hours
to days to years. Think of short-term stability as ADEV
from tau 1 to 100 seconds. Then think of phase noise as
ADEV for the range of tau 0.0000001 to 1 second.

> Does anyone on this list have information and or
> experience with Sapphire based oscillators?  For example
> how does the aging rate compare to quartz?

There's a fine set of CSO (Cryo-Cooled Sapphire Oscillator)
papers is at:


In particular I'd recommend "Introduction to Microwave
Sapphire Oscillators", by G. J. Dick:



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