Is it correct to assume that if you collect data every 10 ms for 10 seconds (1000 data points in total), you could actually split that data set into 100 sets of data at 1 seconds for 10 seconds (10 data points in each set), which would have the same statistical quality (I am sure caveats would apply) as a single data set of 1000 data points collected at one second interval over a total period of 1,000 seconds?
Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -----Original Message----- From: Jim Lux <[email protected]> Sender: [email protected] Date: Mon, 15 Aug 2011 06:31:21 To: <[email protected]> Reply-To: Discussion of precise time and frequency measurement <[email protected]> Subject: Re: [time-nuts] frequency stabilty question On 8/14/11 8:10 PM, Paul Cianciolo wrote: > Folks, > > I amtrying to understand some of the terms used here quite often. > I quoted this from Wikipedia > > An Allan deviation of 1.3×10−9 at observation time 1 s (i.e. τ = 1 s) should > be interpreted as there being an instability in frequency between two > observations a second apart with a relative root mean square(RMS) value of > 1.3×10−9. > > Does this mean the observations made were at the very begining and the very > end of the 1 second time. > If so what value about all the values in between? What happens if the > oscillator deviated far worse than this during the interrim. > A measurement at tau=1 second doesn't say anything about what happened at shorter intervals. > > Or does the measurement consist of making measurements every cycle during > that 1 second and then entering all those values into a formula that accounts > for them all?? > Nope.. It's if you measured the frequency (instantaneously) at one second intervals, and calculated the standard deviation, that would be the ADEV for tau=1 second. measure at 10 second intervals and you get ADEV(Tau=10sec), etc. That's why you typically see an ADEV as a series of performances at different taus. You can also fill in the gaps in the curve, to a certain extent, because physical oscillators have constraints on what the ADEV can do (i.e. you're not likely to see 1E-9 at tau=1 second, 1E-5 at tau=2 seconds, 1E-10 at tau=3 seconds) In fact, if you do the ADEV measurement and it's NOT a nice curve and has spikes and weirdnesses, that starts to tell you have either a measurement system problem or a problem with your frequency standard. (sort of like spurs in a phase noise plot from 120Hz line interference, or reference clock leakage) As an example of measurement system problems, it's pretty common to see a "hump" in ADEV around 500-1500 seconds (around 15-20 minutes) because of temperature effects on the test equipment or unit under test as the airconditioning/heating cycles on and off. > Maybe a very basic tutorial on this topic would help but I cant find one > > > Signed very confused, > Thank You > > PauLC > W1VLF > _______________________________________________ > 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. _______________________________________________ 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. _______________________________________________ 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.
