[time-nuts] Cs stability

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Jul 16 21:30:36 EDT 2007

Tom Van Baak wrote:
> The given specs are conservative (in typical HP style) but
> I would guess the best ADEV numbers are only for laboratory
> conditions. Someone from Agilent/Symmetricom might want
> to comment on this.
>> OF COMMERCIAL ATOMIC CLOCKS", Pekka Eskelinen claims to
>> have measured a phase temperature coefficient of 100ns/degree
>> for commercial Cs clocks in 1999.
> I'll comment after I read it. But the 100ns/degree value doesn't
> make sense because that's phase instead of frequency units.
> Did he mean 100 ns per day per degree? Or per 200 hours,
> or 2000 hours, etc. If the latter, that represents a per-degree
> frequency shift of 100 ns / 2000 h = 1.3e-14 which sounds
> about right to me for a cesium tempco. It also depends on the
> model: the tempco of a vintage hp 5060A or hp 5061A is likely
> worse than a modern 5071A, for example.

Yes it can make sense.
Place one Cs clock in a chamber where the ambient temperature can be 
adjusted to various fixed temperatures. Compare the phase of its 
5/10MHz  and/or PPS outputs with respect to those of another Cs standard 
held at constant temperature. The observed phase shift sequence may then 
be fitted to both frequency shift and a fixed (for a given temperature) 
phase shift components. Repeat for a range of temperatures and plot the 
(temperature dependent) fixed phase shift component as a function of 


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