This sounds interesting enough and I would appreciate any notes or insight on doing this. I have a PRS10 and several GPSDOs that I would like to evaluate for performance on my scope.
Many thanks. ---- Dana Whitlow <k8yumdoo...@gmail.com> wrote: > I cheered when I saw Dave B's "silly question", for > then I realized that I'm not the only one who likes > to measure things with an o'scope. > > I had purchased a GPSDO a few weeks before and > had been observing its behavior relative to a free- > running Rb by watching 10 MHz sinewaves drift with > respect to each other as an aid in setting the Rb's > frequency. However, I was seeing enough fairly > rapid random drift to limit the usefulness of this kind > of observation. It dawned on me that I was sometimes > seeing drifts of several ns over the course of just > several seconds, thus implying that sometimes the > relative frequency error between the two sources was > reaching as high as roughly 1E-9. I wanted to be able > to capture and plot a somewhat extended run of data > so I could try to understand this behavior better. > > Being TIC-less, I decided to see what I could do with > my o'scope, which is a Chinese-made 2-channel DSO > with synchronous sampling by the two channels and > with a respectable trace memory depth (28 MSA per > channel). > > I began this effort in earnest a couple of days before I > saw Dave's question, and have only now brought it to > a sufficient state of completion to feel justified in reporting > some results. > > I am presently able to record about 45 minute's worth of > data as limited by the 'scope's trace memory, but my XP > computer's RAM space limits me to processing only about > 35 minutes of that in a seamless run. Over that time > span I've seen a peak relative frequency discrepancy of > about 1.4E-9, with a handful reaching or exceeding 1E-9. > I've also measured average frequency differences between > the source's a a few parts in 10E11. > > Most of the effort went into developing a C program to do > the processing and then correctly scaling and displaying > the results in a form which I considered useful to me. This > processing of course had to deal with an off-frequency and > drifting 'scope timebase, which is *horrible* compared to the > quantities under measurement (as expected from the outset). > > Present indications are that at this level of GPSDO mis- > behavior, the results I'm viewing are about 20 dB higher > than the basic floor, which I am still characterizing. I > believe that the floor is limited primarily by uncorrelated > sampling jitter between the two 'scope channels. > > If there is an expression of interest in this technique, I'll > publish a detailed description of the technique and some > plots showing results, probably in the form of an attachment > in pdf format. > > Dana > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.