Steve, > Hmmm... If I measured a 10MHz oscillator for a 1/10 second, I > could achieve, at best, 1ppm accuracy. Now my measuring > system has a non accumulating error in the ms range, say <1s, > so this would be totally unworkable. If I sampled for 1s, > best would be .1ppm accuracy...
this is a common misbelieve but simply not true. You need not buy the most advanced stuff. Even a moderate surplus counter like the RACAL DANA 1991/1992/1996 will get you < 1ppb (b, not m!) resolution @ 1 s. Since more than 30 years counters do no more simply "count" but work with lots clever electronic tricks inside! 73s de Ulrich, DF6JB > -----Ursprungliche Nachricht----- > Von: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Im Auftrag von Steve Rooke > Gesendet: Donnerstag, 2. Oktober 2008 07:37 > An: Discussion of precise time and frequency measurement > Betreff: Re: [time-nuts] Testing frequency using NTP > > > Hmmm... If I measured a 10MHz oscillator for a 1/10 second, I > could achieve, at best, 1ppm accuracy. Now my measuring > system has a non accumulating error in the ms range, say <1s, > so this would be totally unworkable. If I sampled for 1s, > best would be .1ppm accuracy, but my measuring errors would > still swamp the result. To make my measuring errors small, I > could make the 1s overhead very small compared to the measing > time period by, say, sampling for 10^6s thereby making the 1s > error 1ppm. Now the 1s error is probably considerably smaller > than that, probably by the order of at least a decade or two. > If it was just .1s error, I could get a result to 1ppm in > about a day and better if I sample of a number of days. > > Cheers, > Steve > > 2008/10/2 Scott McGrath <[EMAIL PROTECTED]>: > > It depends on how accurately you want to measure the oscillator > > frequency with your approach short term you probably would > not be able > > to measure the oscillator offset any better than a few > parts in 10-5 > > longer term probably a few parts in 10-7 might be possible as you > > could compute the allen deviation and fit a curve through > the median > > values. > > > > NTP from a stratum 3 clock is only going to be precise to a few > > milliseconds and for meaningful accuracy you need another order of > > magnitude. This is part of the function of the drift file in xntpd > > in which the daemon attempts to compensate for the drift and offset > > inherent in cheap oscillators used in computer applications. > > > > > > - Fellow nuts am I all wet here or have I missed a technique > > -- > Steve Rooke - ZL3TUV & G8KVD > 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. > _______________________________________________ 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.
