[time-nuts] Disciplining Rubidium

[John Miles]

> > 11) Short-term phase noise; the GPS-Rb sources don't seem to
> > be as clean as the better GPS-OCXO packages.
>
> And EXACTLY THIS was what the OP was asking after!

More quantitatively: in this file, the red trace is from my Thunderbolt, the
green trace is from a Datum 9390 Rb-GPS standard's 10 MHz output, and the
white trace is from the same Thunderbolt after passing through an HP 5087A
distribution amp.  (Awhile back someone was asking what effect those
distribution amps had on the phase noise of a 10 MHz signal; this shows
about the same result as what John Ackerman measured at 5 MHz on his own
5087A.)

The actual FRS-C is quite a bit cleaner but still nowhere near as good as
the Thunderbolt.

Also worth noting is that the Datum's output is quite a bit noisier than it
was several months ago when I measured it with (very) different hardware.  I
wouldn't take the green trace in this graph to the bank until I've had a
chance to repro that earlier measurement.  Still, either way, it's
definitely much noisier than the Thunderbolt.

-- john, KE5FX

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