Hi If you look at Tom’s data, he very definitely has a peak to peak in the 5 to 7 ns range over a 24 hour period. He also gets the expected auto correlation spikes.
Bob > On Apr 17, 2017, at 4:38 PM, Bob Stewart <b...@evoria.net> wrote: > > Hi Tom, > The reason I express so much confusion over this is because I don't see the > wild phase excursions on my GFS units that people insist will happen due to > ionospheric effects. Is this because they are rare events, and I just > haven't been saving data during a bad time? I notice in your example page, > you aren't seeing them, either during your 8+ day capture of the Tbolt. > > Bob > > > From: Tom Van Baak <t...@leapsecond.com> > To: Discussion of precise time and frequency measurement <time-nuts@febo.com> > Sent: Monday, April 17, 2017 3:05 PM > Subject: Re: [time-nuts] Three-cornered hat on timelab? > > Bob S, > > Here's an example of a one week GPSDO run: > > http://leapsecond.com/pages/tbolt-8d/ > > IIRC, this was a default, untuned, self-surveyed TBolt. You can see some > level of daily variations -- probably a mix of sky view, survey error, > ionosphere, multi-path, sidereal effects [1], temperature (antenna, cable, > GPSDO, reference), etc. It takes some time and equipment to sort out which is > which, but even a simple test like this can give you an upper bound. > > /tvb > > [1] Fun GPS orbit stuff here: > http://leapsecond.com/pages/sidereal/index.htm > http://leapsecond.com/pages/sidereal/14years.htm > http://leapsecond.com/pages/sidereal/sv.htm > http://leapsecond.com/pages/gps-orbit/ > > > ----- Original Message ----- > From: "Bob Stewart" <b...@evoria.net> > To: "Bob kb8tq" <kb...@n1k.org>; "Discussion of Precise Time and Frequency > Measurement" <time-nuts@febo.com> > Sent: Monday, April 17, 2017 9:33 AM > Subject: Re: [time-nuts] Three-cornered hat on timelab? > > > Hi Bob, > OK, thanks. I've kicked off a 7 day run of a GFS against the PRS-45A. That > should be long enough to separate out the GFS from the PRS' drift direction > from the ionosphere. > > Bob > > > > From: Bob kb8tq <kb...@n1k.org> > To: Bob Stewart <b...@evoria.net> > Cc: Discussion of precise time and frequency measurement <time-nuts@febo.com> > Sent: Monday, April 17, 2017 11:28 AM > Subject: Re: [time-nuts] Three-cornered hat on timelab? > > Hi > The ionosphere is the culprit in terms of the daily swing. The swing is a > function of the goodness of fit between the GPS broadcast dataand the > ionosphere as it impacts the satellites you are using. There is no rime or > reason to it beyond that. If you get “lucky” things don’t move much. If you > live in exciting times, things move quite a bit. Unless you go to something > like an L1/L2 receiver, the GPS module you use has little to do with it > (unless it’s broke ….). Yes there are some fiddly little qualifiers relating > to being at the north or south pole and GPS coverage (along with space > weather impacts). Very few of us do our runs at either location :) Just for > reference, the area of concern also hasat least one day each year where the > sun sets for < 1 hours. > Bob > > > > > On Apr 17, 2017, at 11:33 AM, Bob Stewart <b...@evoria.net> wrote: > Hi Bob, > Oh, I had completely forgotten about the many runs you gifted us with back > then. Fortunately, I kept all of them in my email archive. I can't compare > like for like, of course, but I think I can work up something that compares > at the larger taus where the 5370 doesn't dominate. > I'm going to run another long term test of my GFS unit against my PRS-45A. > The problem, the issue that made me ask for data is that everything from > phase plots to ADEV plots of my unit are just so much better than the KS. In > addition, I don't see the large ionospheric swings on my GFS unit that you > and Bruce and others have spoken about. This bothers me a lot. Could it be my > location here in Houston? Could it be the Ublox LEA-6T compared to the much > older Motorola in the KS? > > Bob > > From: Bob kb8tq <kb...@n1k.org> > To: Bob Stewart <b...@evoria.net> > Cc: Discussion of precise time and frequency measurement <time-nuts@febo.com> > Sent: Monday, April 17, 2017 7:55 AM > Subject: Re: [time-nuts] Three-cornered hat on timelab? > > Hi > The data I have on the KS boxes was posted to the list back when they were.a > hot topic. I’m sure it is still in the archives.I’m guessing it’s not quite > what you are after. > > The closer the devices are to each other the better the technique works. A > simple way to look at it is as an attenuation. If it knocks noise down 10:1, > the worst unit should be no more than 10X noise than the best unit. How much > things are knockeddown is a function of the length of the runs compared to > the longest tau. For a 10:1 ratio of tau to run, attenuation of noise by 10:1 > is very optimistic. You usually need something beyond 100:1 to get that sort > of performance. A lot depends on the noise involved. Some types of behavior > simply don’t work well with the technique. > The KS box goes from “better than” to “worse than” and back to “better than” > most atomic standards you would compare it to overa range of tau from 0.1 S > to 1,000,000 seconds. To get the 1,000,000 second data accurately, you would > need a 100,000,000 secondrun. The simple answer there is that nobody has that > kind of time or that reliable a setup. Even the three month run to get > good100,000 second data is a challenge. None of that relates to three corner > hat stuff, it’s just the confidence bars on ADEV. It givesyou another (say) > 100:1 wait on top of the three corner stuff. > Now toss in the basics of GPS. Depending on the day, you will get <10 ns to > >100 ns swing over a 24 hour period. Today may or may not be the same as > tomorrow. That’s with a “perfect” L1 setup. The variation comes from the > ionosphere and the fact thatthe GPS data does not allow you to fully correct > for it. In addition, you will get some interesting bumps related to > constellations and your local antenna setup. Any GPSDO that is quartz based > will happily follow the 24 hour swing in the GPS from the ionosphere. At > 100,000 seconds, a 100 ns swing is 1x10^-12. That’s a lot of disruption. It > most certainly is not the sort of thing that ADEV expects to pop up in the > middle of a run. > The simple answer to all this is “don’t go there”. Three corner hat is fine > for short term stuff. It’s a mess for long term runs. Getting datathat is > good enough for a long term ADEV run out of a three corner setup is a major > struggle. The time for the correlation to knock downthe noise on top of the > time to get good ADEV data gets you into impractically long runs. > Bob > > > > > On Apr 16, 2017, at 10:16 PM, Bob Stewart <b...@evoria.net> wrote: > Hi Bob, > OK, I give up. Try as I might, I can't fudge things enough to make any sense. > I did run a set of 1 hour tests that seemed to confirm what I can infer from > the phase plots in timelab, but anything longer than that and the curves > either contradict the phase plots, or there are large gaps in at least one > trace, or a trace is even missing entirely. Oh well. I seem to remember > reading that the 3c-hat was only useful in comparing similar devices. The KS > just isn't close enough to what I'm trying to compare it to, I guess. > > If you or anyone else has an ADEV plot of the KS against some local standard > (for any length of time, any standard, even just a bare OCXO that is not a > Trimble 34310-T) could you please share it with me? I'm looking for relative > peformance, not a definitive test. Of course if you also have one of a > 34310-T against the same standard, that would be great! > > Bob > > From: Bob kb8tq <kb...@n1k.org> > To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency > measurement <time-nuts@febo.com> > Cc: John Miles <j...@miles.io> > Sent: Thursday, April 13, 2017 7:19 PM > Subject: Re: [time-nuts] Three-cornered hat on timelab? > > Hi > > There are a number of papers from the 70’s and 80’s digging into three corner > hat data. The net result often > would turn out to be “less than zero” noise on one of the DUT’s. Since that’s > physically impossible the technique > got a bit of “attention”. The Cliff Notes version of the results is that > simultaneous measurements were the key > to getting decent results. The closer to “same time” (as in microseconds or > nanoseconds) the better. Even with very careful > data collection, odd things can still happen. Phase noise pops up at crazy > low levels or ADEV goes to bizarre > numbers. In many ways a TimePod (or other ADC based setup) is ideal for > getting the data synchronized. Running > all three devices on one is by far the best way I have seen to make the > technique work. It still can have problems, > but less so that other ways of doing it. > > Bob > > > >> On Apr 13, 2017, at 7:16 PM, Bob Stewart <b...@evoria.net> wrote: >> >> Hi John, >> I had a chance to think about this some more after I pressed the send key. >> The ionospheric effects are certainly going to be different if the distance >> in time between tests is large. And, of course, there is the fact that the >> KS has a pretty old receiver compared the Ublox I use, so that even the >> reaction to the ionosphere is likely to be different. So, I thought I'd >> experiment with some runs with both GPSDOs in holdover to see if that would >> even the score, so to speak. Of course then I have the temperature variable, >> so it's never going to be perfect. >> Anyway, thanks for the help. If I get anything that seems useful out of >> this, I'll post links to the data. >> Bob >> >> From: John Miles <j...@miles.io> >> To: 'Discussion of precise time and frequency measurement' >> <time-nuts@febo.com> >> Sent: Thursday, April 13, 2017 6:01 PM >> Subject: Re: [time-nuts] Three-cornered hat on timelab? >> >> Longer runs would be better to the extent that they give you smaller error >> bars in your tau range of interest, certainly. But any effects that >> influence one of your runs but not the others will render the 3-cornered hat >> solution questionable, if not outright invalid. Only through many repeated >> runs can you learn to tell the bogus data from the good stuff. So I'd make >> shorter runs at first, until you're sure you know what you're looking at. >> >> >> >> It doesn't matter which source is applied to the start versus stop channel, >> as long as the assignments are consistent with the source labels you apply. >> I would use frequency-count mode to simplify things, at least at first. This >> is already a very challenging measurement for all the reasons mentioned. >> >> >> >> -- john, KE5FX >> >> Miles Design LLC >> >> >> >> >> >> From: Bob Stewart [mailto:b...@evoria.net] >> Sent: Thursday, April 13, 2017 8:41 AM >> To: Discussion of precise time and frequency measurement; John Miles >> Subject: Re: [time-nuts] Three-cornered hat on timelab? >> >> >> >> Hi John, >> >> >> >> Thanks! With lesser equipment, such as the 5370A, would longer runs be >> better? I used a set of 1 hr runs and the result wasn't quite what I had >> expected. However, it may be that I had mislabeled the files, and thus got >> the sources confused. Of course, it may be that the ionospheric effect was >> grossly different between the three tests. So, with a 5370, Source A would >> be the START input and Source B would be the STOP input, right? For my >> testing, the sources are all 10MHz signals, and I'm driving the EXT input >> with 1PPS from a GPSDO. >> >> >> >> >> >> Bob >> >> _______________________________________________ >> 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. >> >> >> >> _______________________________________________ >> 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. > > > > > > > > > > > > _______________________________________________ > 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. > _______________________________________________ > 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. > > > > _______________________________________________ > 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. _______________________________________________ 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.
