NIST Technical Note 1337: Characterization of Clocks and Oscillators

a mean frequency of 4.01 parts in 10 13 . Applyingthe m~thods described in section IV and section V,....e generalted the a (t)ydiagram shown in figure).2.• //ID'10'"!ifCS 'PC \02 ~~ CS (,()1Dl!I'T~FIGURE 7.3FIGURE 7.2One observes that the last two points are proportionalto t"+1 and on~ is suspicious 01 a significantfr@qulI!ncy drift.'~ "J T1 "1.";..: ~1.4f.J:l5f~"t'-Hr,10." I,If one ca1clJlatll!s the drift k.nowing that 10o)r} is equal to theefrift times 12 a drift ofl~ 22 )( 10-11. per day ;s obtained. A 1inear leastsquares to the frequency was removed and sections FIGURE 7.4IV and V were applied again. The linear leastsquares fit sho\oted a drift of 1.23 x 10-14 perday, which is in excellent agreement with thepreviou$ calculated valu@obtained 1rom 0y(r).Typically, the linear least squalres will give amuch bll!tter estimate of the 1inear frequency drHtthan will the estimate from a (r) being propor""·1 ytional to rFigure 7.3 gives the plot 01 the time residualsafter removing thE! linear llast squares andfigure 7.4 is the corresponding 0y(t) YS. t diagram.From the 33 days 01 data, we have used thE!90% conti dence i nterva1 to bracket the stabi 1i tyest.imates and Dne sees a reasonable f1t cerrll!spendingto white noise frequency mDdulation at a't-,,~"9­'t,~Slevel of 4.4 x 10- 11 t-~. This seemed excl!!Ssive FIGURE 7.5')t1O-I2't~~18TN-3l