Hi Tom, 2009/4/9 Tom Van Baak <[email protected]>: > 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 -- Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW Omnium finis imminet _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
