Hi A little more detail on the AtomiCron stuff: It’s an add on (= paid) feature on the Septentrio Mosiac-T GNSS modules. There are products out there that have this module built in. Typically the ability to enable AtomiCron is possible on those products. Some devices are full up GPSDO’s others are a bit more basic. With a basic device, you can often put your 10 MHz local standard into it. It will report the performance of your standard. You get a high resolution number that is typically accurate to about 1 ns. Yes, this assumes your GNSS antenna is in a good ( = unobstructed) location. One ns at 1 second does not do you much good for characterizing your GPSDO. That’s true of a number of devices, not just the Mosaic-T. It commonly comes up with regard to frequency counters. You already have something in the 2x10^-13 vicinity. A 1 ns accuracy device will hit this level at 5,000 seconds. Since your OCXO’s likely only make it to 1K seconds, this leaves you with a bit of a gap. In an ideal setup, your references would overlap. Making this happen does indeed get complicated. The “big deal” is that your AtomiCron reference does indeed keep getting better as tau gets longer. You will ultimately hit the limits of the clock ensemble driving the GNSS systems. That’s way lower than most simple lab setups can accomplish. There also is a bit of hand waving going on with this math. One could indeed get a bit more detailed in that regard. Bob > On Mar 3, 2026, at 1:29 PM, John Miles via time-nuts <time-nuts@lists.febo.com> wrote: > > (JohnA: any idea why my replies have several blank lines between paragraphs? I’m only using one blank line when I type.) > > > > The 50 Hz ripple usually means that there is a large loop area in the ground wiring of your test setup, possibly because the 53100A and/or PC is plugged into a separate power circuit than the sources being measured. It’s best if you can plug every piece of equipment involved into a single circuit, ideally the same power strip. You could also reduce the ripple by selecting 5 Hz measurement bandwidth. The drawback to using oscillators this good is that you’ll see artifacts that otherwise would be buried in the noise, and that’s definitely true in your case. > > > > Note that all3aDev.png does not have the 3-cornered hat view turned on; if hitting ctrl-h doesn’t work, check your source labels. > > > > The real problem is simply that you can’t measure the long-term stability of a source like this without a better long-term reference source. The use of two independent references can be a massive win in short- and medium-term measurements, but in the long run, common environmental effects usually rule out much improvement. Even if that’s not an issue, you will have to run for weeks to improve the results at taus on the order of one day, so it just isn’t practical. > > > > For this type of work you really need to set up an AtomiChron-enabled GPSDO such as one of the Sparkfun GNSS disciplined oscillators or Viavi PNT-6250 DOCXO-based units (disclosure: I work with Viavi but not on that product.) This will give you a stable reference in the same class as a passive maser at much less upfront expense. Basically you want a GNSS-disciplined oscillator with the highest-precision AtomiChron service and the lowest-grade holdover oscillator available -- i.e., no rubidium standard in the case of the Viavi units. > > > > -- john > > > > ---------------------- > > From: Srihari Padmanaban <srihari.p03@gmail.com> > Sent: Tuesday, March 3, 2026 5:15 AM > Thanks for your reply. > > > > Yes OCXO1 and OCXO2 are excellent oscillators (Oscilloquartz 8607)… > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com