Oleg, On 05/10/2018 10:46 AM, Oleg Skydan wrote: > Hi > > Now I have some questions. As you know I am experimenting with the > counter that uses LR calculations to improve its resolution. The LR data > for each measurement is collected during the gate time only, also > measurements are continuous. Will the ADEV be calculated correctly from > such measurements?
Many assume yes, actual answer is no or well, it depends. ADEV assumes brick-wall filtering up to the Nyquist frequency as result of the sample-rate. When you filter the data as you do a Linear Regression / Least Square estimation, the actual bandwidth will be much less, so the ADEV measures will be biased for lower taus, but for higher taus less of the kernel of the ADEV will be affected by the filter and thus the bias will reduce. It was when investigating this that Prof Enrico Rubiola and Prof Francois Vernotte invented the parabolic deviation PDEV. > I understand that any averaging for the time window > larger then single measurement time will spoil the ADEV plot. Correct. > Also I understand that using LR can result in incorrect frequency estimate for > the signal with large drift (should not be a problem for the discussed > measurements, at least for the numbers we are talking about). That is a result of not using a LR/LS method supporting drift, at which time its effect on frequency estimation is greatly reduced. LR only for phase and frequency model, i.e. only linear components, is unable to correctly handle the quadratic nature of linear drift. Thus, by using a LR model that supports it, the quadratic terms influence on frequency estimation can be reduced. > Does the ADEV plots I got looks reasonable for the used "mid range" > OCXOs (see the second plot for the long run test)? You probably want to find the source of the wavy response as the orange and red trace. 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.