On Thu, September 17, 2015 8:26 pm, Can Altineller wrote: > b. If we put two rubidium sources, and have them warm up and stabilize, > and then hook up a 2ch scope and observe the pattern, will there be a > phase difference between the 10mhz signals? (without the scope doing any > syncing)
Any two sources which do not have a way to force synchronization to some external reference at startup will always have a phase difference. Did you really mean a phase difference (i.e. the oscillators did not start oscillating at exactly the same time) or a change in the phase difference over time (i.e. the oscillators are not at exactly the same frequency)? The answer in both cases is yes, but the reasons are different. You can eliminate the starting phase difference by having a gate circuit in the oscillators to allow holding the output off until a synchronizing signal is received. That will get them started together, but if the synchronizing signal is a one time event then the two will drift apart over time, either because of differences in the environment due to influence of temperature, magnetic field, barometric pressure, etc. on the oscillating mechanisms, or just imperfections in the mechanisms themselves that prevent operating at exactly the theoretical absorption frequency of rubidium. To eliminate the drift in phase difference you have to discipline the oscillator frequency with an external reference of some kind. Of course that is talking in absolutes, and there is probably a point where you no longer care because the differences are very small. The typical language used to describe the difference of one frequency referenced to another is parts per million, meaning 1 Hz frequency error of offset per MHz output, so 1Hz off for a 1MHz oscillator, or 10 Hz off for a 10MHz oscillator, etc., sometimes written in scientific notation as 1 x 10^-6. Similarly for parts per billion, 1 x 10^-9, and parts per trillion as well, 1x10^-12, but it seems like the scientific notation is much more common than the English language description when you get to those levels (possibly due to differences in American and historical British definition of billion and trillion, see Wikipedia references to long scale and short scale). -- Chris Caudle _______________________________________________ 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.