-------- Markus Kleinhenz via time-nuts writes: > But I think i got some pointers that can put you on your path.
One (always?) overlooked metric, is the frequency spectrum of the zero-crossings, of the phase difference input to the PLL. (NB: This obviously require good resolution of the phase error, including application of the "negative sawtooth" correction, otherwise the "hanging bridges" noise will swamp the signal you are looking for.) If your loop is (too) tight, the PLL will chase every wiggle in the GPS signal and your phase difference input to the PLL will change sign all the time. If your loop is (too) loose, the PLL will not follow the GPS signal as close as it should, and the phase difference will only rarely change sign, if your OCXO/Rb drifts, possibly not ever. My heuristic is that when you plot the histogram of the time between zero-crossings, you want the "bulge" on the low side of, but close to, the "allan-intercept" (Ie: where the OCXO and GPS allan curves cross.) If you are working with 3rd order PLLs (predicting frequency drift), plotting separate histograms of the duration of positive and negative phase inputs helps: The more they overlap, the better your drift estimate. I have tried my hand at the math of this phenomena, but it disappears into dark corners of math text-books, where I cannot follow its trail. Poul-Henning -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@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. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
