[time-nuts] Cs standard stability

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Mar 4 04:44:16 EST 2017


That doesn't seem inconsistent with the specs given the contribution of the 5370A to the measured ADEV is likely to be of the same order as the PRS45A spec. The ADEV of the GPSDO also needs to be taken into account. The contribution of the 5370A to ADEV will gradually become insignificant compared to the PRS45A specs as Tau increases. To achieve an accurate measurement of ADEV for Tau=1s you will need something better than the 5370A together with a low ADEV source (for Tau = 1s).

> On 04 March 2017 at 18:26 Bob Stewart <bob at evoria.net> wrote:
> I hooked up my PRS-45A yesterday, just to do some ADEV comparisons with my GPSDO.  Unfortunately, the GPSDO seems to be better by almost two points at all tau as measured on my HP 5370A and plotted by Timelab.  So, can I infer from that that the OCXO in the PRS has a problem, or could it be something as stupid as a bad cap?  Or do I just not understand the specs and the PRS isn't up to my expectations?  The PRS docs show the unit as 3E-11 at 1s tau, and I'm seeing about 4.25E-11 at 1s, so maybe it's the latter.
> NOTE: The test setup for this is 1PPS from a well-aged GPSDO to the 5370's start input, and 10MHz from either a different GPSDO or the PRS to the stop input.
>  As best as I can tell looking through the holes in the case (still running the tests), the PRS has an MTI 250-0827 5MHz OCXO.  I've got one of the Lucent KS units that I don't care much about, so maybe the MTI 260-0624 5MHz in that will work?  Both are 5MHz, but I don't know whether both are 12V at this point.  And, of course, I don't know whether making the swap to an MTI 260 OXCO will benefit the PRS.
> Any comments or educated speculations are welcomed.
> Bob - AE6RV
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