[time-nuts] Datum 9390 Rb phase noise

[John Miles]

> > Yours is actually better than spec...  my Efratom FRS-C manual says the
> > spec is -70 at 1 Hz offset, -110 at 100 Hz, -130 at 1 kHz.  The notation
> > is a bit odd though -- it says "dBc/sqrt(Hz)".
>
> You're looking at the Thunderbolt trace, I'm guessing... I'm only
> getting -117 dBc/Hz at 1 kHz out of the Datum, -142 dBc/Hz at 1 kHz out of
> the Thunderbolt.

Just measured the FRS-C by itself, and it does appear to meet that
specification ( http://www.thegleam.com/ke5fx/compare.gif, 30KB).  So Datum
is just running it through a noisy signal chain on the way to the back
panel.

> > My understanding is that the compact telecom Rbs put FM on the reference
> > as part of the lock mechanism; that makes the phase noise fairly ugly.

I can see that happening with a scope during the first minute or two of
warmup time, but it goes away after that.

-- john, KE5FX