I like the sliding waveforms and a variation used by General Radio with their circular sweep 1109A comparison oscilloscope. I built a slightly different model:
Franke, John M.: “A Circular Sweep Frequency Calibrator,” The AMSAT Journal, Volume 31, No. 4, July/August 2008, pp. 4-7. Reprinted in Proceedings of Microwave Update 2008, Bloomington, Minnesota, October 17-18, pp. 167-170, published by the American Radio Relay League (ARRL), Inc. > On October 1, 2018 at 6:54 PM Dana Whitlow <[email protected]> wrote: > > > I've done the Lissajous thing, but it takes an extra bit of effort to > work out the phase angle. I've always gone back to the sliding > waveforms display for simplicity. > > But I'll admit the Lissajous pattern is a lot prettier, and looks great > in Sci Fi movies. > > Dana > > > On Mon, Oct 1, 2018 at 4:06 PM Richard (Rick) Karlquist < > [email protected]> wrote: > > > No one mentioned using Lissajous patterns for comparing > > frequencies if the scope has an XY mode. Google Lissajous > > if interested. > > > > Rick N6RK > > > > On 10/1/2018 11:40 AM, Bryan _ wrote: > > > Interested as well > > > > > > -=Bryan=- > > > > > > ________________________________ > > > From: time-nuts <[email protected]> on behalf of Chris > > Burford <[email protected]> > > > Sent: October 1, 2018 6:20 AM > > > To: Discussion of precise time and frequency measurement > > > Subject: Re: [time-nuts] Oscilloscope-based measurements of frequency > > stability > > > > > > 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 <[email protected]> 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 -- [email protected] > > >> To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > >> and follow the instructions there. > > > > > > _______________________________________________ > > > time-nuts mailing list -- [email protected] > > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > > and follow the instructions there. > > > _______________________________________________ > > > time-nuts mailing list -- [email protected] > > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > > and follow the instructions there. > > > > > > > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
