Poul-Henning Kamp wrote: > In message <[EMAIL PROTECTED]>, "Ulrich Bangert" writes: > >> Hello Paul-Henning, >> >> www.tmo.jpl.nasa.gov/progress_report/42-121/121G.pdf >> >> definitely uses no FFT but uses a theoreme from geometry to estimate the >> signal's frequency and the rest is a two dimensional non-linear fit for >> amplitude and phase. But i am starting to understand how a FFT might be >> helpfull too. >> >> Does it involve finding the maximum of the frequency spectrum by >> interpolating between frequency bins and then find the matching >> (interpolated) phase bin? >> > > That would depend on your sampling rate. > > If you sample a 1Hz signal 96k times a second, interpolation between > bins would probably just be a waste of time. > > Alternatively, you could apply a really steep band-pass filter around > 1 Hz. Something like an 1131 pole FIR filter, and then find > the zero crossing geometrically using the three points around the > zero line. > > You are still left with the problem of apportioning the measured instability between the 2 oscillators/signals being compared. Unless you know one of them is significantly less noisy than the other it is not possible to accurately apportion the instability between them. A 3 cornered hat where 3 oscillators are compared using 3 mixers can help if the instabilities of all 3 oscillators are statistically independent. It is also better if all 3 oscillators have similar instabilities.
A comparison of N oscillators using 0.5*N(N-1) mixers is even better. Bruce _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
