Hi RMS:
https://en.wikipedia.org/wiki/Root_mean_square <https://en.wikipedia.org/wiki/Root_mean_square> When we talk about things like “6 sigma” in QA, the sigma is the RMS. Bob > On May 3, 2017, at 1:44 AM, Bob Stewart <[email protected]> wrote: > > Hi Tom, > Could you clarify the term RMS? Is there some sort of calculation I need to > do on the raw data to get the RMS value? > I'm going to begin by doing a fresh 8 hour test of GPSDO Unit 1 vs GPSDO Unit > 2, with the same conditions as the tests involving the PRS. IOW, the 5370 is > being clocked by GPSDO Unit 2, and the trigger for the EXT input to the 5370 > is from GPSDO Unit 2. START is from GSPDO Unit 1 and STOP is from GPSDO Unit > 2. The ones I have on hand show about 4E-11 at 1s tau. > > After that, I'll run an 8 hour test of raw 1PPS from a LEA-6T against the > PRS. Since I don't really trust the PRS, I'll use GPSDO Unit 2 to clock the > 5370. If you really don't want the GSPDO to clock the 5370, I'll run the > same test using the internal 10811 as the clock, to compare the difference. > > I also ran into an old test of the 5370 where START (10MHz) was fed by a > GPSDO and STOP (10MHz) was fed by the same GPSDO but with (I think) a 20 ft > cable from START to STOP. I'll probably want to rerun that, as well, but it > was an almost straight line from 2E-11 at 1s tau in that dataset. Still, > that test will verify that the 5370 hasn't degraded. Bob > > From: Tom Van Baak <[email protected]> > To: Discussion of precise time and frequency measurement <[email protected]> > Sent: Wednesday, May 3, 2017 12:02 AM > Subject: Re: [time-nuts] Three-cornered hat on timelab? > > Hi BobS, > >> I've also made the timelab file (compressed by 7z) available here: >> http://evoria.net/AE6RV/Timelab/GFSvsCS.4.22.17.7z > > Thanks for sharing that. To follow-up on recent emails... > > When you start to push the limits of your own test equipment it's good to > employ tricks such as 3-corner hat in order to get a few dB better > measurement. But there's a limit to that. And you probably don't want me to > suggest that you run 3 GPSDO, 3 counters and 3 cesiums all simultaneously. > > I've attached two plots showing 4+ days of your GPSDO data and 4+ days of a > TBolt (factory defaults, *untuned*) > > bob-gpsdo-3.gif -- Notice how much your GPSDO (blue trace) wanders all over > the place. > > bob-gpsdo-5.gif -- ADEV comparison. See below for comments. > > 1) > When I look at the ADEV for your data set it's pretty clear that the limiting > factor on the left (short tau) is the resolution of your 5370A counter. > That's why the TBolt looks better. Don't worry about that. > > 2) > In the middle of the ADEV plot it would appear that both your 5370A counter > and your PRS-45A cesium reference are sufficiently good to properly measure > your GPSDO. That's good. The TBolt looks bad in the middle but that's simply > because it was using a way-too-short default time constant. With proper > tuning the red trace would be mostly flat out to 1000 seconds. > > 3) > From the look of the phase plot and the ADEV plot it almost seems to me like > your PRS-45A is the limiting factor on the right (long tau). If so, it would > explain the lack of diurnal and sidereal effects in your data. If you look at: > http://leapsecond.com/pages/tbolt-8d/sigma1.gif from > http://www.leapsecond.com/pages/tbolt-8d/ > you'll note the sidereal "blip" is below 4e-14. Your ADEV doesn't get near > that level. > > > I say this because a rule-of-thumb is that a good M12+T timing receiver > should get you down to 3 ns per day RMS. And a good ublox-6T can get you to 3 > or 2 ns per day RMS. Your data shows something more like 5 ns -- which for a > GPSDO is worse than no GPSDO at all. So something's wrong. What set of > experiments can you perform to locate the problem? Or, what experiments can > you perform that don't require buying expensive gear? > > My first suggestion is for you run a standalone GPS timing receiver like a > M12+T or ublox-6. Put all your GPSDO away. Just use that OEM board, and your > TIC, and your PRS-45A. Collect sawtooth data too. You should get down to 2 or > 3 ns RMS. > > /tvb > > ----- Original Message ----- > From: "Bob Stewart" <[email protected]> > To: "Discussion of Precise Time and Frequency Measurement" > <[email protected]>; "Magnus Danielson" <[email protected]> > Sent: Thursday, April 27, 2017 9:48 AM > Subject: Re: [time-nuts] Three-cornered hat on timelab? > > > Hi Magnus, > Try as I might, the weather and the local power company had other ideas about > my long term capture. I'm running everything but the 5370 from a UPS. I guess > I'm going to have to get batteries for my other UPS and run the 5370 from > that. A one second power loss was all it took to stop the test. > > Anyway, I did manage to get 376,238 points of data. The data is captured on a > 5370A. The external clock input and the STOP channel are fed by the 10MHz > from my PRS-45A. The START channel is fed by the 10MHz from one of my GPSDOs. > The EXT channel is fed by the 1PPS from another of my GPSDO units. "EXT ARM" > is enabled. So, essentially, at every 1PPS pulse, the phase difference > between the two 10MHz feeds is captured. > > I've attached a screenshot of the phase plot which can also be found > here:http://evoria.net/AE6RV/Timelab/Screenshot.png > I've also made the timelab file (compressed by 7z) available here: > http://evoria.net/AE6RV/Timelab/GFSvsCS.4.22.17.7z > > So, back to my question: Where are the large ionospheric phase moves? This > question has been causing me doubt since I started on this project. Or don't > I still have enough data collected for this to happen? > > Bob > > ----------------------------------------------------------------- > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > From: Magnus Danielson <[email protected]> > To: Bob Stewart <[email protected]>; Discussion of precise time and frequency > measurement <[email protected]> > Cc: [email protected] > Sent: Tuesday, April 18, 2017 1:09 AM > Subject: Re: [time-nuts] Three-cornered hat on timelab? > > Hi Bob, > > That is a good solution indeed. Good luck with that measurement run! > > One of the fun stuff with Timelab is that you can walk by and check the > developments. I've found that very useful for long measurements (as in > hours and days). > > I prepared a cesium for one vendor, and initially they did not care so > much, but then they saw more deviations between the receivers, so they > wanted to sort it out, but discovered that they could not cancel out the > common mode of GPS signals (and its shifts), so then firing up that > cesium was the right thing. I remember writing support emails while > waiting for the airplane in Madrid airport, happy that they was doing a > first run for the right measurement reason. :) > > Cheers, > Magnus > > On 04/18/2017 04:25 AM, Bob Stewart wrote: >> Hi Magnus, >> Today I started a long run against my PRS-45A. Maybe this time I won't have >> a power outage. I'll see what it tells me in a few days. >> Bob_______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
