> Le 17 juin 2017 à 07:55, Lifespeed via time-nuts <time-nuts@febo.com> a écrit > : > > Not too surprising to read locking two crystal oscillators together without > using a physical cable is difficult to impossible. Essentially what I am > looking for is the phase alignment accuracy (and phase noise) one would get > PLL’ing one oscillator to the other using a cable, but over a longer > distance. Some modest phase noise degradation might be acceptable, but not > an order of magnitude. Clearly not a trivial problem. Yes, the jitter (phase > noise) typically accomplished from a PLL phase comparing at 100MHz is better > than what one could get “locking” to GPS. It was just a thought, apparently > not a realistic one. Thanks for disabusing me of that notion. > > > > Sorry I can’t go into a lot of detail about the overall system block diagram, > but this one aspect of the design does just reduce to phase-locking two > oscillators over a distance. >
Why not just have ONE frequency generator locked to GPS if you want, and just distribute the output with equal length cables. It would mean a cable roll to store at one end, but you would be assured of phase coherency at both. No? > > > Bob, I think I understand your post processing method refers to the reality > that all broadcast signals from which phase information could be extracted > are modulated, introducing complications that would not be present with a > simple carrier. > > > > Lifespeed > > > > Hi > > > > > > On Jun 16, 2017, at 7:24 PM, life speed <life_sp...@yahoo.com> wrote: > > > > That sounds like phase-locking the oscillators to a local radio transmitter. > Not sure there is any difference post-processing vs. real time. > > > > The advantage is that you capture a much wider bandwidth signal than you can > lock to. That lets you extract better “instantaneous phase” information. With > the narrow band loop normally used for locking, loop dynamics get into the > picture. That on top of the RF propagation issues is a bit of a mess. It also > is quite possible to capture multiple radio (or TV or …) transmissions and > post process against all of them. > > > > The bottom line is still that “many degrees” at 100 MHz is far more practical > than “tenth of a degree”. There are very few options if your application > really does need roughly a tenth of a degree. > > > > Bob > > > > > > > > > > - Lifespeed > > > > _____ > > Hi > > > > A far more common approach is to let the two oscillators free run and to > record something like a local broadcast station. > > You then post process all of the data to give you the phase accuracy. One of > several gotcha’s is the stability of any > > radio link at the level you are looking for. > > > > Bob > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. "The power of accurate observation is commonly called cynicism by those who have not got it. » George Bernard Shaw _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
