I should have added, if you do all of the above, the improvement in stability over just using a sawtooth-corrected PPS is not all that spectacular, a factor of two or three. I'll post a plot of some data tomorrow.
Cheers Michael. On Wednesday, 15 June 2016, Michael Wouters <michaeljwout...@gmail.com> wrote: > If you followed the link to www.openttp.org and are wondering where the > software is, follow the link on the home page to GitHub and then look in > the Develop branch. The ublox branch is for the new '8' series receivers. > > Cheers > Michael > > On Tuesday, 14 June 2016, Michael Wouters <michaeljwout...@gmail.com > <javascript:_e(%7B%7D,'cvml','michaeljwout...@gmail.com');>> wrote: > >> Hello Angus >> >> If you have 3 rubidiums of similar stability + 3 counters, you could >> do a 3-cornered hat. >> >> Otherwise, GPS common view to a better clock may be an option. If you >> are reasonably close to a national standards lab, you might be able to >> use their time-transfer files to compare your rubidiums with their >> time scale - not everyone makes them publically available though. >> Otherwise, if there is an IGS station near you, you could use the >> station RINEX files and IGS clock solutions which are freely >> available. Many IGS stations have a H-maser as the local clock. But it >> may be just as good to simply use the comparison with GPS time >> inherent in the time-transfer file. >> >> The advantage of generating a time-transfer file is the possibility of >> then improving upon the various corrections broadcast by GPS, >> effectively repeating what the GPS receiver does to generate its >> realization of GPS time but with better data. >> >> With post-processing, the short to medium term (less than 1 day) >> performance can be improved a bit as you are suggesting when you >> referred to "atmospheric issues". Improved ionospheric models are >> available or if there is an IGS station nearby, for example, the >> measured ionosphere could be used. Other improvements can be had with >> good antenna coordinates and using final orbits in the processing. >> >> What can you use for your time-transfer receiver ? Some low-cost >> single-frequency receivers are suitable eg the Trimble Resolution T. >> The essential requirement is the availability of raw code >> measurements - with these you can generate CGGTTS time-transfer files >> and/or RINEX observation files. >> >> At least part of the software infrastructure to do this exists: the >> OpenTTP project (www.openttp.org) has software for CGGTTS and RINEX >> file generation for a few older,single frequency receivers, with >> support for some other,current receivers under active development. >> There is other software around, but it is orientated towards dual >> frequency receivers and carrier phase processing. >> >> Although it would be relatively straightforward to hack in use of >> improved ionosphere, using final orbits is a bit harder since these >> are not parameterized the same way as the broadcast orbits. Maybe >> someone on time-nuts has software to do the conversion (and this would >> have to be hacked into the OpenTTP software, rather than the final >> time comparison). >> >> The sort of performance you get on a zero baseline is a TDEV of a few >> ns - you can extrapolate frequency stability from that. >> On a 1000 km baseline, you can compare two Cs to better than 1 part in >> 10^13 @ 1 day. >> >> All of the above is software-oriented, whereas you seem to be looking >> for a hardware solution, but that's what I know best. >> >> Cheers >> Michael >> >> On Tue, Jun 14, 2016 at 6:16 PM, Angus <not.ag...@btinternet.com> wrote: >> > Hi, >> > >> > I'm planning to test some rubidiums again, but since Santa never did >> > get me that hydrogen maser I asked for, I'm still stuck with ordinary >> > gps timing receivers as a separate medium to long term reference. The >> > atmospheric issues are probably the main ones I would like to get rid >> > of, although the more errors removed the better. >> > >> > It does not have to be done in real time, but even an single test run >> > would last weeks, so there could be a lot of data to tie together. >> > >> > It would really need to be something that actually exists rather than >> > just an idea of how it might be done, since I really just don't have >> > time for any more major projects anytime soon. I've found from >> > experience that too much time spent making the test gear etc means >> > that I don't get the time to actually use it! >> > >> > I'm also looking for something that's not too expensive - like up to >> > hundreds rather than thousands of pounds. >> > A good cesium or 2+ frequency gps with relevant options might be fine, >> > but also rather out of my price range. >> > >> > BTW, I do plan on uploading the end results, in case anyone is >> > interested. >> > >> > >> > If anyone knows of some way to do this, (or even has something >> > appropriate they want to sell) I'd appreciate hearing about it, on or >> > off-list. >> > >> > Thanks, >> > Angus. >> > _______________________________________________ >> > 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.