[time-nuts] Rb short-term noise (was RE: Is this a cesium...)

John Miles jmiles at pop.net
Fri Aug 24 16:37:25 UTC 2012

> The PRS-10 has a huge spur at 60 Hz.
> What were you using for a power supply?  (Or what should I be asking?)

I turned off the spur display for that plot, to reduce the visual clutter.
But especially when several spurs are clustered together, TimeLab can fail
to detect some of them, and any spurs that aren't detected can't be removed.
There are actually three spurs near 60 Hz in that plot, two of which were
detected and one of which was missed (the one you saw.)  One of those will
likely be an AC line spur, while the other two are of unknown origin.
(Here's the same plot with spur amplitudes plotted.)

The PRS10's spur specification is -130 dBc, so these would be pretty close
to the spec.   -130 dBc is not a very strong spur, in the grand scheme of
things.   I wouldn't want to see an OCXO with a non-line-related spur at
-130 dBc, but anything as complex as a rubidium standard will probably have
a few spurs of that magnitude here and there.

As far as line-related spurs go, no attempt was made to minimize ground
loops between the PRS10 and the reference, their power supplies, the PC, or
anything else, so I wouldn't worry about them in this case.

-- john, KE5FX

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