[time-nuts] Improving on basic L1 timing

Michael Wouters michaeljwouters at gmail.com
Wed Jun 15 02:21:42 EDT 2016


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 <michaeljwouters at 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 <michaeljwouters at gmail.com
> <javascript:_e(%7B%7D,'cvml','michaeljwouters at 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.again at 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.
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>


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