I just put the results of some tests of 2 "Time-Nuts Special" Thunderbolts, as well as 2 Z3801As, at http://www.febo.com/pages/gpsdo_comparison/
I learned an interesting (and important) lesson in doing these measurement. I initially measured the pairs of GPSDO against each other (e.g., one TBolt as "reference" and the other TBolt as "DUT"). In theory, if the two oscillators are identical, and if their noise is uncorrelated, the results of the pair can be used to deduce the results of the individual units. However, in this case doing so gave a very optimistic view -- the TBolts were better than the pair of Z3801As! Another set of measurements comparing the GPSDOs against an independent reference revealed that the first measurement was a lie. I guess you can think of it like this. Picture two OCXOs that both age at the same rate and in the same direction. Because they drift together, measuring their relative phase hides their actual drift and makes them look better than they are. On the other hand, if they were drifting in opposite directions, they would look worse than they are. An identical aging trend is a "correlation" even though it's external to the things we usually think of. John _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
