Hi Volker, On 12/22/2012 04:55 AM, Volker Esper wrote:
Although I am dog-tired it gives me no peace... I come to the following conclusion: - The long term Allan deviation gets worse, as long, as the effect of EFC compensating is in the range of tau - But: It gets back to its normal value after that - The short term deviation, however, increases slowly, but it doesn't settle. It's increasing more and more. So it is the short term stability, that is affected, rather than the long term stability. Am I right or wrong? Perhaps I'm to tired to decide.
You short term will rise with 1/tau in ADEV is due to white noise. This noise may be due to the oscillator or (many times) your measurement rig. This is expected from theory (see Allan Deviation on Wikipedia).
A free-running OCXO will have a D*tau/sqrt(2) rise due to linear drift. If it is beeing steered it would captured by the control loop and depending on it's properties there will be some marginal errors due to it.
A free-running OCXO will also experience temperature shifts and that will create a ripple effect in the ADEV/MDEV. If it is being steered the PLL loop would have issues fighting it which could leave traces in the ADEV/MDEV plot.
For systematic effects like these, the ADEV/MDEV/TDEV plot isn't the ideal tool. phase/frequency/drift plots and FT of them might be more useful.
However, as you might have realized, a single event of temperature event like this averages out on the large scale of things. ADEV and friends isn't a good tool for transient properties, as it is a statistical tool to establish noise levels of various types. For that purpose single freak events of systematic effect needs to be averaged out or even taken out.
Doing your plots to show how they vary over time illustrates this in a good way. The "event" is not part of the long-term noise properties.
Cheers, Magnus _______________________________________________ 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.
