[time-nuts] Code for phase noise and allan variance

Poul-Henning Kamp 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    
Never attribute to malice what can adequately be explained by incompetence.

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