Bruce, 2009/4/10 Bruce Griffiths <bruce.griffi...@xtra.co.nz>: > Just dont get too carried away. > Remember that the Hadamard deviation is only insensitive to linear > frequency drift. > If the drift is quadratic for example then it will affect the Hadamard > deviation.
Point well taken. In that case we need a new deviation measurement with 4 elements then :-) 73, Steve > Bruce > > Steve Rooke wrote: >> Hi Tom, >> >> 2009/4/9 Tom Van Baak <t...@leapsecond.com>: >> >>> I use it sometimes when I need to. But note that in most cases >>> you do NOT want to ignore drift. If you measure an OCXO for >>> the purpose of using it in a clock or appliance or radio or test >>> equipment you really do want to know if it has drift or not. ADEV >>> will show this, while HDEV will not. So you have to be careful >>> about using statistics that deliberately and quietly ignore effects >>> that may be important to your application. >>> >> >> Indeed, I was thinking that HDEV would be a good tool to characterise >> free running OCXOs with it's insensitivity to drift but, of course, I >> would use ADEV to measure the performance of a GPS locked system or >> one running in holdover mode. >> >> >>> But before you run off and use HDEV for everything note that >>> the other practice that is far more common -- simply remove >>> frequency drift from the raw data before computing an ADEV >>> on the residuals. If you look at plots in professional journals you >>> will often find comments to the effect that phase, frequency, or >>> drift offsets have been added or removed prior to making said >>> phase, frequency, or stability plots. >>> >> >> I had no intent to use HDEV exclusively, it seems like a useful tool >> to analyse free-running oscillators to measure the affects of noise >> while screening out drift (which we have some means of handling in >> holdover circuits). As a selection tool it seemed quite useful and I >> was asking if others felt the same way. >> >> Agreed, it is possible to factor out drift by pre-processing the data >> and then using just ADEV to compare all aspects of any open or closed >> system. >> >> >>> Here, to see the difference that HDEV makes (or not) see: >>> http://www.leapsecond.com/pages/hdev >>> >> >> It seems to have an effect removing some of what must be drift with >> the OCXO plot but adds nothing to the PPS one. Do I take it that the >> OCXO was free-running and the PPS was locked to GPS, as this would >> account for the differences? >> >> >>> The command line program that I use (ADEV3) these days: >>> Tool for ADEV, MDEV, HDEV: >>> http://www.leapsecond.com/tools/adev3.exe >>> >>> Source code (compiles in windows, bsd, or linux) >>> http://www.leapsecond.com/tools/adev3.c >>> >> >> Thanks for the pointers, I'll have a look at this instead. >> >> 73, >> Steve >> > > > _______________________________________________ > 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. > -- Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW Omnium finis imminet _______________________________________________ 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.