[time-nuts] PN on internal/external references and Cross correlation

John Miles john at miles.io
Thu Sep 28 20:58:23 EDT 2017

> Thanks for clarifying this issue! I may use references with close-in PN
> (1Hz-1kHz) 10 dB noisier than the DUT, however as you said it may
> require an overnight run for 1 Hz offset, which isn't the nice part... I
> assume then that speeding up the measurement process can only be
> obtained using references sources at least quieter than the DUT.

A 10-dB deficit may not be too bad, since the performance improvement isn't linear with time.  If your instrument takes 8 hours to drop the measurement floor by 20 dB, for instance, it will only take 4 hours to achieve 18.5 dB of improvement, or 2 hours for 17 dB.   So if each of the references is 10 dB noisier than the DUT, their effect will be mostly gone after 2 hours.

-- john, KE5FX
Miles Design LLC

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