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

[Tijd Dingen]

> > 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.

Correct. And for now the working assumption is that the input signal is
sinusoidal, with just a smattering of noise.

> 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.

Yeah, I thought of that one. But it becomes prohibitive in terms of resources
real fast. ;)

> 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.

There's an idea. I will be doing a curve fit of the time stamps anyway, so I
get the time deviations from the fit for "free". Normalize the time deviations 
into
phase deviations, and use that. Worth a try, thanks!

Fred