Chuck Chuck Harris wrote: > n3...@aol.com wrote: > >> So can any one bring it down a few clicks and explain the accuracy thing to >> this balding hippie? >> >> I'm leaning towards ham radio applications. GPSDO are rated in one way like >> 1 X 10 to something. Ham radios are >> coming with "High Stability" oscillators that are rated in ? PPM. >> >> In laymen's terms what do those numbers mean and how do they relate to each >> other? >> > > They convey the same information as an accuracy percentage, only they > allow for an easier to understand number for higher stability sources. > > For example, an oscillator that is accurate to 1%, is accurate to > one part in 100, or expressed in scientific notation, 1 part per 10E2. > > Wrong, it should read: 1 part in 1E2. 1E2 is actually shorthand for 1x10^2 .
For example see: http://en.wikipedia.org/wiki/Scientific_notation This is the way the E notation is implemented on HP scientific calculators. > Most people on this group consider that pretty (well awfully, actually) > crude. > > As you get to more and more stable frequency sources, you might hear > of 1 part per million, or 1 PPM, or 1 part in 10E6. In percentages, > that would be 0.0001%. > > 1 PPM is 1 part in 1E6 . You are just perpetuating a misinterpretation that was relatively common in some old OCXO datasheets. > And as you become a time-nut, you start to talk of parts in 10E12, which > in percentages would be 0.0000000001%... Which is just too cumbersome > to use. You have to count the zeros every time you look at the number, > and you still aren't sure what it means. > > Any specification that tells of the accuracy of a frequency standard > needs some additional information... notably, a time frame over which > the accuracy is valid. So you will hear things like 1PPM/year, or > 1 part in 10E12 per second. > > 1 part in 10E12 per second is actually 1 part in 10^11 per second. > Some information about environmental conditions would also be useful. > > Also, implicit in an accuracy specification is +/- which creates an > error band for the error to be contained within. > > When one becomes a true time-nut, one starts to worry about trends in > stability issues, and at that point, statistical analysis becomes > important, and you start to talk of things like Allen-Variances. > > -Chuck Harris > >> Hope this doesn't start to much controversy on the board. >> >> 73 Chris >> >> >> >> Bruce _______________________________________________ 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.