Which means, after a bit of scrounging for some BNC to SMA adapters, I have some plots worth using (more or less) of my clock! Background info: my clock's main purpose is to be a GPS-disciplined NTP server on an Arduino Due clone board. As such, accuracy beyond tens to hundreds of microseconds isn't really relevant. But for purely time-nut reasons, it has an Rb oscillator (cheap surplus X72), and for similar reasons it has a PPS output generated by the CPU timer. I didn't hack the Due apart to replace the crystal, so the CPU clock (84MHz) is asynchronous from the Rb, which has some limitations, but also introduces a nice little bit of dither The TICC is set up with 10MHz from a Spectracom NetClock, chA from a (probably insufficiently thermally stabilized) LTE-Lite, and chB from my clock. Output is in Timelab mode. A representative bit of the phase plot: http://i.imgur.com/cRXv9ia.png You can see all the quantization noise on my clock, but also that in the ~100s region, it does better than the LTE-Lite. You can also see the nice smooth (at short time) plot of the LTE-Lite which gives me some good faith in the TICC. ADEV plot so far: http://i.imgur.com/DLb15rt.png Timelab loses the thread a little bit and comes up with negative computed deviations for my clock for some tau. Not sure how much of that is due to instrument limitations, and how much is due to the noise being not-really-independent, since all three clocks are GPS receivers, with rather nearby antennas. Still, more than I've ever seen before! Andrew

Hi Andrew -- There seems to be more than a little magic involved in getting sane three-corner measurements. I've gotten best results when the run is long enough to have many data points per tau, and also that results when you're noise limited tend to go imaginary. Finally, I think things work best when the three sources have similar noise processes, e.g., looking at 3x OCXO or 3x Rb or whatever. I'd love any of the experts to jump in on this, as I've not done much beyond basic experiments, and I don't have the maths to comprehend the subtleties. John ---- On 02/24/2017 12:59 PM, Andrew Rodland wrote: > Which means, after a bit of scrounging for some BNC to SMA adapters, I > have some plots worth using (more or less) of my clock! > > Background info: my clock's main purpose is to be a GPS-disciplined > NTP server on an Arduino Due clone board. As such, accuracy beyond > tens to hundreds of microseconds isn't really relevant. But for purely > time-nut reasons, it has an Rb oscillator (cheap surplus X72), and for > similar reasons it has a PPS output generated by the CPU timer. I > didn't hack the Due apart to replace the crystal, so the CPU clock > (84MHz) is asynchronous from the Rb, which has some limitations, but > also introduces a nice little bit of dither > > The TICC is set up with 10MHz from a Spectracom NetClock, chA from a > (probably insufficiently thermally stabilized) LTE-Lite, and chB from > my clock. Output is in Timelab mode. > > A representative bit of the phase plot: http://i.imgur.com/cRXv9ia.png > > You can see all the quantization noise on my clock, but also that in > the ~100s region, it does better than the LTE-Lite. You can also see > the nice smooth (at short time) plot of the LTE-Lite which gives me > some good faith in the TICC. > > ADEV plot so far: http://i.imgur.com/DLb15rt.png > > Timelab loses the thread a little bit and comes up with negative > computed deviations for my clock for some tau. Not sure how much of > that is due to instrument limitations, and how much is due to the > noise being not-really-independent, since all three clocks are GPS > receivers, with rather nearby antennas. Still, more than I've ever > seen before! > > Andrew > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. >

On Fri, Feb 24, 2017 at 7:08 PM, John Ackermann N8UR <jra@febo.com> wrote: > Hi Andrew -- > > There seems to be more than a little magic involved in getting sane > three-corner measurements. I've gotten best results when the run is long > enough to have many data points per tau, and also that results when you're > noise limited tend to go imaginary. Finally, I think things work best when > the three sources have similar noise processes, e.g., looking at 3x OCXO or > 3x Rb or whatever. > Thanks. I'm not even complaining here, like I said, this is more visibility than I've had in the past, and the TICC is looking pretty good. As for more points, that was just the first 9 or so hours of a 24-hour run, which is now completed. At the end of that, it's more reasonable: http://i.imgur.com/7v3obqy.png — although I'm certainly not putting much faith in anything past 1000s. And the non-hat plot: http://i.imgur.com/xWTsqCX.png . Andrew

FWIW, here is a quick test I ran on my TICC, assuming the attachment makes it. "TICC base" was a Trimble Thunderbolt reference and PPS. The reference for the other traces was an FE-5680A with an LTE Lite on ChA and Trimble PPS on ChB. The GPS antennas are indoors and entirely sub-optimal. The LTE Lite is in a Hammond enclosure and using the antenna supplied with the eval kit sitting on top of a metal file cabinet. The result seems to be about as expected for the LTE Lite. The Trimble typically doesn't track many satellites so I'm not expecting great results. On Fri, Feb 24, 2017 at 11:58 PM, Andrew Rodland <andrew@cleverdomain.org> wrote: > On Fri, Feb 24, 2017 at 7:08 PM, John Ackermann N8UR <jra@febo.com> wrote: > > Hi Andrew -- > > > > There seems to be more than a little magic involved in getting sane > > three-corner measurements. I've gotten best results when the run is long > > enough to have many data points per tau, and also that results when > you're > > noise limited tend to go imaginary. Finally, I think things work best > when > > the three sources have similar noise processes, e.g., looking at 3x OCXO > or > > 3x Rb or whatever. > > > > Thanks. I'm not even complaining here, like I said, this is more > visibility than I've had in the past, and the TICC is looking pretty > good. As for more points, that was just the first 9 or so hours of a > 24-hour run, which is now completed. At the end of that, it's more > reasonable: http://i.imgur.com/7v3obqy.png — although I'm certainly > not putting much faith in anything past 1000s. And the non-hat plot: > http://i.imgur.com/xWTsqCX.png . > > Andrew > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. >