I have to show my ignorance here, because this has been bothering me for a while, and, I wonder if there is a relatively simple answer. This question has to do with frequency accuracy and stability only. Also, let's talk of long term like 24 hours or more, so let's ignore phase noise and just concern ourselves with long term accuracy/stability. If I have three separate oscillators, let's say a Rubidium, an OCXO and a TCXO all with EFC's capable of closing the loop to lock to GPS, what kind of absolute frequency difference should I see amongst the three at any given time, random times, or, over the entire test period. Let's also make it simple and say all three are at 10 MHz nominal, unlocked to GPS. When locked, and properly designed with a narrow loop filter, I would expect the long term accuracy to be very close amongst all 3 oscillators. Certainly better than a few parts in 10^-11. First, am I wrong in this assumption? In either case, crystals, and even Rubidium cells do age, while at different rates, so, it is possible, that if lock with GPS is lost for some reason, because the oscillator may have drifted/aged out of loop range, it cannot be disciplined again. I, for the time being, also assume that the EFC on all 3 oscillators has a range wide enough to keep the oscillator locked even as it ages. Are the narrow loop bandwidths and wide EFC ranges contradictory? So, to reiterate the question, if I was clear enough, what kind of frequency excursions should I anticipate to see amongst my three disciplined oscillators in lets say 24 hours, or in a month. Assume GPS disciplining was working all of that time (can I even assume that with aging?). BTW, how is my assumption regarding the oscillators aging? If the oscillator basic frequency determining element drifts out of lock range, during lock, will it stay in lock? - Thanks in advance for any enlightenment - Mike
Mike B. Feher, N4FS 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
