[time-nuts] Code for phase noise and allan variance
phk at phk.freebsd.dk
Mon Jun 27 18:46:44 EDT 2005
In message <20050628.004037.48976141.cfmd at bredband.net>, Magnus Danielson write
>> Does anyone have code which will take an amplitude vs. time input
>> stream and output phase noise and/or allan variance?
>I guess you could do it that way, but really, it would be alot of data at a
>high sampling rate to make any usefullness.
You're wrong Magnus :-)
You overlook that the A/D converter gives you much more information
about the timing of a zero-crossing than just the sample number:
You can interpolate the zero-crossing to subsample accuracy and
that way get far *better* resolution than the HP5370 which otherwise
holds the single-shot crown.
I have played a lot with this with a 12bit 20MHz ADC card I have, and
the USRP does 64MHz sampling which is a lot better.
If your signal is relatively noise-free and of good amplitude I
would not at all be surprised to see single-shot timings well into
the pico-second regime, (compared to the 15nsec a digital use of
64MHz would give).
And as I suggested in an email a couple of days ago: It would be
almost perfect for phase-noise measurements as well, thanks to
the dual inputs.
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
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