David L. Mills wrote: > It's easy to make your own Allan characteristic. Just let the computer > clock free-run for a couple of weeks and record the offset relative to a > known and stable standard, preferable at the smallest poll interval you > can. The PPS from a GPS receiver is an ideal source, but you have to > jerry-rig a means to capture each transition. > > Compute the RMS frequency differences, decimate and repeat. Don't take > the following seriously, I lifted it without considering context, but > that's the general idea. Be very careful about missing data, etc., as > that creates spectral lines that mess up the plot. > > p = w; r = diff(x); q = y; i = 1; d = 1; > while (length(q) >= 10) > u = diff(p) / d; > x2(i) = sqrt(mean(u .* u) / 2); > u = diff(r) / d; > x1(i) = sqrt(mean(u .* u) / 2); > u = diff(q); > y1(i) = sqrt(mean(u .* u) / 2); > p = p(1:2:length(p)); > r = r(1:2:length(r)); > q = q(1:2:length(q)); > m1(i) = d; i = i + 1; d = d * 2; > end > loglog(m1, x2 * 1e6, m1, x1 * 1e6, m1, y1 * 1e6, m1, (x1 + y1) * 1e6) > axis([1 1e5 1e-4 100]); > xlabel('Time Interval (s)'); > ylabel('Allan Deviation (PPM)'); > print -dtiff allan > > Dave
And for those of you who didn't recognize it, that's MatLab code. Danny _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions