Hi Warner, Does it mean I should divide the 10 MHz down to 1 Hz output and use the 5370 to measure TI compared to it's internal timebase once per second, and feed that to the computer, store it to a file and feed the output to AlaVar? (obviously, the divider would have to use synchronous counters)
Or should I work directly on the 10 MHz output? The 5370 can average up to 100k samples, so by averaging 100k samples and polling the GPIB once/sec, would I be correct if I use the computer to average those further down to 2/sec, 4/sec and so on as needed before feeding the data to Alavar? Now, let's assume I have a big hard drive (250 GB + 120 GB at the moment, with probably close to a total of 200 GB available), other than computing time (which may not be negligible), how can I determine the best acquisition interval? (as the one that will give me meaningful data in the shortest amount of time) I understand AlaVar only works in batch mode (no real time capability), so I have to collect a certain amount of data "blindly" before I can find out if it is any good. If I am checking a GPS disciplined oscillator, that will take several hours at a time and I am trying to speed up the process, at least to make sure the procedures and algorithms are OK. See, you can't provide answers without getting more questions :-) Thanks Didier M. Warner Losh wrote: > Just a quick note on this topic. I'll not be able to answer all your > questions, but here's a few. > > Allen Variance (or Allen Deviation) is usually used to measure clock > stability over 1s or longer. As this is a way to judge the stability > of an oscillator, very short term numbers tend to be less useful. > This means that fast data collection rates end up having lots of > redundant data that contributes little added benefit to the > calculations, but has large storage requirements. If you are > computing a Tau of 100s, for example, 10Hz vs 1Hz data will only give > a factor of 3 better confidence interval (the standard deviation of > the avarage at a Tau of 100s, which goes as the square root of the > number of samples), but you'd have a 10x increase in storage. > > Allen Variance usually is measured at 1s, 2s, 4 (or 5s), 10s, 20s, > etc up to some fraction of the period of time the data covers. The > fraction is again determined by the type of deviation and the number > of points used to calculate the number. > > Warner > > _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts