> > 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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