[time-nuts] Calculate spectral content from a series of zero crossing time stamps?

[Poul-Henning Kamp]

In message <224676.41616.qm at web120905.mail.ne1.yahoo.com>, Tijd Dingen writes:

>>From what I could find so far, one method to go about this is use a
>Lomb/Scargle Periodogram. And specifically the method by Press & Rybicki that
>extirpolates the unevenly timed samples to an regular timed mesh, after which
>a regular DFT is done.

Just knowing the time of the zero-crossings is very little information
to go by, but you have to make some kind of assumption about the
perfection of curve shape between those points, in order to say
anything meaningful.

The dirty but not necessarily quick way to analyze the data, is to
turn it into a +/- 1 squarewave at 1GHz (1/1ns), low-pass filter
it with a 15-18 kHz cut-off and do the usual FFT.

The other option is to normalize your zero-crossings, so you get
signed numbers telling how early/late they happen, and do a FFT
on that.  Its too early in the morning for me to be able to see
how you transform the resulting phase-deviation spectrum to a
normal frequency offset plot, but a few tests with synthetic data
should tell you that.

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