Re: [time-nuts] Frequency over fiber (was WWV and legal issues)
FWIW the round-trip delay on our 900km White Rabbit link looks like so (lower graphs. upper are a local Cs-clock vs. the fiber-time): http://monitor.mikes.fi/mikes_kaja/ No fault-lines, earthquakes, or volcanoes in Finland I'm afraid. That's a standard 2-fiber (separate TX and RX fibers) DWDM system with amplifiers, multiplexers, and dispersion-compensation fibers - in addition to the actual fiber-spans. diurnals on the 10.5 ms RTT seem to be around 80ns this time of the year. Larger jumps are fiber/equipment repairs. The recent earthquake paper on the London-Paris link is this one I think: https://arxiv.org/ftp/arxiv/papers/1801/1801.02698.pdf Anders On Sun, Sep 2, 2018 at 11:14 PM Peter Vince wrote: > Hi Magnus, > > Could you please give us some idea of the magnitude of these effects? > Even if just whether we are talking about nano, pico, or femtoseconds? > > Thank you, > > Peter > > > On 2 September 2018 at 12:17, Magnus Danielson > > wrote: > > > Hi Gerhard, > > > > I see that this became a separate thread. > > ... > > ... > > > > Acoustical sensitivity, low frequency changes. > > > > For optical clocks and frequency transfer, just the vibration from > > traffic and other activity causes disturbances which disturbes the group > > delay. What is done for these links is to actively compensate then using > > a return path and closing the loop with a controller, very much like a > > PLL. The length of the loop limits the bandwidth and hence how high up > > the compensation can be done, so for longer stretches, this needs to be > > repeated. They have now built links from PTB to SYRTE and NPL. > > > > Temperature shifts are slower, but also compensated though the active > loop. > > > > Close proximity to strong power-currents have also been shown to cause > > modulations, so separate from power-cables if you can. > > > > Remember that the end nodes have very stable clocks, so their effects > > can be taken out of the equation. For other setups, such as telco > > operation, that's a completely different ballgame. > > > > Cheers, > > Magnus > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Frequency over fiber (was WWV and legal issues)
Hi Magnus, Could you please give us some idea of the magnitude of these effects? Even if just whether we are talking about nano, pico, or femtoseconds? Thank you, Peter On 2 September 2018 at 12:17, Magnus Danielson wrote: > Hi Gerhard, > > I see that this became a separate thread. > ... > ... > > Acoustical sensitivity, low frequency changes. > > For optical clocks and frequency transfer, just the vibration from > traffic and other activity causes disturbances which disturbes the group > delay. What is done for these links is to actively compensate then using > a return path and closing the loop with a controller, very much like a > PLL. The length of the loop limits the bandwidth and hence how high up > the compensation can be done, so for longer stretches, this needs to be > repeated. They have now built links from PTB to SYRTE and NPL. > > Temperature shifts are slower, but also compensated though the active loop. > > Close proximity to strong power-currents have also been shown to cause > modulations, so separate from power-cables if you can. > > Remember that the end nodes have very stable clocks, so their effects > can be taken out of the equation. For other setups, such as telco > operation, that's a completely different ballgame. > > Cheers, > Magnus > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Frequency over fiber (was WWV and legal issues)
Question: Supposing you buy a bundle of a couple of dozen fibers inside one outer jacket: Can anyone give me an idea of how well the individual fibers are likely to be matched in delay, and in delay tempco? Dana On Sun, Sep 2, 2018 at 1:46 PM Poul-Henning Kamp wrote: > > > In message , Bob kb8tq > writes: > > > That’s why they design a certain amount of “slack” into the structure. > > As far as I know, thermal expansion and contact losses are far > bigger dimensioning factors, except for a few very active fault-lines. > > At these fault-lines and/or with very important fibers, special and > site-specific precautions are usually taken. > > For terrestial faultlines, the cheapest and easiest mitigation is > to cross the fault-line on poles with a slack messengerwire. > > For oceanfloor faultlines, plenty of slack and an oblique crossing > is the best we've come up with yet. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Frequency over fiber (was WWV and legal issues)
In message , Bob kb8tq writes: > That’s why they design a certain amount of “slack” into the structure. As far as I know, thermal expansion and contact losses are far bigger dimensioning factors, except for a few very active fault-lines. At these fault-lines and/or with very important fibers, special and site-specific precautions are usually taken. For terrestial faultlines, the cheapest and easiest mitigation is to cross the fault-line on poles with a slack messengerwire. For oceanfloor faultlines, plenty of slack and an oblique crossing is the best we've come up with yet. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Frequency over fiber (was WWV and legal issues)
Hi Motion at a fault line can be a bit chaotic. As that motion stretches (or stops stretching) the cable the delay is likely to change. How much does it change? no idea. If vibration messes with it, stretch should as well. Hopefully the fiber “spiralt” inside the outer jacket is enough to keep things from snapping very quickly. Ground shifts around for a lot of reasons even if you are not on a fault line. That’s why they design a certain amount of “slack” into the structure. Bob > On Sep 2, 2018, at 11:07 AM, Azelio Boriani wrote: > > Why should there be a variation in the fiber's delay across an active > fault line? The fiber could only break at the fault line, lay down > more fiber than needed, to compensate the movement, and the delay > doesn't change. > On Sun, Sep 2, 2018 at 4:51 PM Bob kb8tq wrote: >> >> Hi >> >> Tidal effects can be very “non linear” as you approach a coast line. Lots of >> change >> over a fairly short distance. If indeed the world decides to put in a global >> PTTI fiber >> system, all of this would get into the mix on some links. It appears that >> the existing >> technology would handle the issues. >> >> Of course there’s still some guy named Bob running that back hoe without >> checking >> for buried lines …..*That* we could test for … likely no need to run the >> experiment. :) >> >> Bob >> >>> On Sep 2, 2018, at 10:07 AM, Tom Van Baak wrote: >>> I suspect there’s a longer list of “slow” environmental effects that are also taken care of with the compensation setup. One would guess that crossing a active fault line would be “interesting”. >>> >>> Yes, here's a back of the envelope calculation for you: >>> >>> - the Pacific Northwest moves on the order of 10 cm per year [1] >>> - 1 meter of time is 1/299792458 = 3.3 ns >>> - 10 cm/year is 3.3 ns / 86400 / 365 = 1e-17 df/f >>> - the best laboratory optical clocks are down to that level of stability [2] >>> >>> On the other hand, in the real world you'd have to convince me that you've >>> found two national timing labs with 1) state-of-the-art optical clocks, 2) >>> which operate as phase (time) standards instead of as frequency standards, >>> 3) or run continuously for a year (instead of a few times per week), 4) are >>> connected by stabilized fiber, 5) that cross plate boundaries moving >>> anywhere near as much as 10 cm/year, and 6) the optical time nuts running >>> the clocks don't already factor geodetic effects like this into their clock >>> comparisons... >>> >>> Unfortunately I won't be able to measure this. Even if John Miles (who also >>> lives near Seattle) and I find optical clocks on eBay some day, and we find >>> a way to run 30 miles of fiber between us without anyone noticing, we are >>> both on the same tectonic plate so the drift cancels out. Note that >>> lunar/solar tidal effects would be common mode to us as well. >>> >>> /tvb >>> >>> [1] >>> https://pnsn.org/outreach/about-earthquakes/plate-tectonics >>> https://www.eoas.ubc.ca/courses/eosc256/jan26_plates_rebound.pdf >>> >>> [2] >>> https://arxiv.org/ftp/arxiv/papers/1309/1309.1137.pdf >>> https://arxiv.org/ftp/arxiv/papers/1704/1704.06323.pdf >>> http://jilawww.colorado.edu/yelabs/sites/default/files/uploads/Sr%20best%20clock_Bloom_Nature.pdf >>> >>> >>> ___ >>> time-nuts mailing list -- time-nuts@lists.febo.com >>> To unsubscribe, go to >>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>> and follow the instructions there. >> >> >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Frequency over fiber (was WWV and legal issues)
Why should there be a variation in the fiber's delay across an active fault line? The fiber could only break at the fault line, lay down more fiber than needed, to compensate the movement, and the delay doesn't change. On Sun, Sep 2, 2018 at 4:51 PM Bob kb8tq wrote: > > Hi > > Tidal effects can be very “non linear” as you approach a coast line. Lots of > change > over a fairly short distance. If indeed the world decides to put in a global > PTTI fiber > system, all of this would get into the mix on some links. It appears that the > existing > technology would handle the issues. > > Of course there’s still some guy named Bob running that back hoe without > checking > for buried lines …..*That* we could test for … likely no need to run the > experiment. :) > > Bob > > > On Sep 2, 2018, at 10:07 AM, Tom Van Baak wrote: > > > >> I suspect there’s a longer list of “slow” environmental effects that are > >> also taken > >> care of with the compensation setup. One would guess that crossing a active > >> fault line would be “interesting”. > > > > Yes, here's a back of the envelope calculation for you: > > > > - the Pacific Northwest moves on the order of 10 cm per year [1] > > - 1 meter of time is 1/299792458 = 3.3 ns > > - 10 cm/year is 3.3 ns / 86400 / 365 = 1e-17 df/f > > - the best laboratory optical clocks are down to that level of stability [2] > > > > On the other hand, in the real world you'd have to convince me that you've > > found two national timing labs with 1) state-of-the-art optical clocks, 2) > > which operate as phase (time) standards instead of as frequency standards, > > 3) or run continuously for a year (instead of a few times per week), 4) are > > connected by stabilized fiber, 5) that cross plate boundaries moving > > anywhere near as much as 10 cm/year, and 6) the optical time nuts running > > the clocks don't already factor geodetic effects like this into their clock > > comparisons... > > > > Unfortunately I won't be able to measure this. Even if John Miles (who also > > lives near Seattle) and I find optical clocks on eBay some day, and we find > > a way to run 30 miles of fiber between us without anyone noticing, we are > > both on the same tectonic plate so the drift cancels out. Note that > > lunar/solar tidal effects would be common mode to us as well. > > > > /tvb > > > > [1] > > https://pnsn.org/outreach/about-earthquakes/plate-tectonics > > https://www.eoas.ubc.ca/courses/eosc256/jan26_plates_rebound.pdf > > > > [2] > > https://arxiv.org/ftp/arxiv/papers/1309/1309.1137.pdf > > https://arxiv.org/ftp/arxiv/papers/1704/1704.06323.pdf > > http://jilawww.colorado.edu/yelabs/sites/default/files/uploads/Sr%20best%20clock_Bloom_Nature.pdf > > > > > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Frequency over fiber (was WWV and legal issues)
Hi Tidal effects can be very “non linear” as you approach a coast line. Lots of change over a fairly short distance. If indeed the world decides to put in a global PTTI fiber system, all of this would get into the mix on some links. It appears that the existing technology would handle the issues. Of course there’s still some guy named Bob running that back hoe without checking for buried lines …..*That* we could test for … likely no need to run the experiment. :) Bob > On Sep 2, 2018, at 10:07 AM, Tom Van Baak wrote: > >> I suspect there’s a longer list of “slow” environmental effects that are >> also taken >> care of with the compensation setup. One would guess that crossing a active >> fault line would be “interesting”. > > Yes, here's a back of the envelope calculation for you: > > - the Pacific Northwest moves on the order of 10 cm per year [1] > - 1 meter of time is 1/299792458 = 3.3 ns > - 10 cm/year is 3.3 ns / 86400 / 365 = 1e-17 df/f > - the best laboratory optical clocks are down to that level of stability [2] > > On the other hand, in the real world you'd have to convince me that you've > found two national timing labs with 1) state-of-the-art optical clocks, 2) > which operate as phase (time) standards instead of as frequency standards, 3) > or run continuously for a year (instead of a few times per week), 4) are > connected by stabilized fiber, 5) that cross plate boundaries moving anywhere > near as much as 10 cm/year, and 6) the optical time nuts running the clocks > don't already factor geodetic effects like this into their clock > comparisons... > > Unfortunately I won't be able to measure this. Even if John Miles (who also > lives near Seattle) and I find optical clocks on eBay some day, and we find a > way to run 30 miles of fiber between us without anyone noticing, we are both > on the same tectonic plate so the drift cancels out. Note that lunar/solar > tidal effects would be common mode to us as well. > > /tvb > > [1] > https://pnsn.org/outreach/about-earthquakes/plate-tectonics > https://www.eoas.ubc.ca/courses/eosc256/jan26_plates_rebound.pdf > > [2] > https://arxiv.org/ftp/arxiv/papers/1309/1309.1137.pdf > https://arxiv.org/ftp/arxiv/papers/1704/1704.06323.pdf > http://jilawww.colorado.edu/yelabs/sites/default/files/uploads/Sr%20best%20clock_Bloom_Nature.pdf > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Frequency over fiber (was WWV and legal issues)
> I suspect there’s a longer list of “slow” environmental effects that are also > taken > care of with the compensation setup. One would guess that crossing a active > fault line would be “interesting”. Yes, here's a back of the envelope calculation for you: - the Pacific Northwest moves on the order of 10 cm per year [1] - 1 meter of time is 1/299792458 = 3.3 ns - 10 cm/year is 3.3 ns / 86400 / 365 = 1e-17 df/f - the best laboratory optical clocks are down to that level of stability [2] On the other hand, in the real world you'd have to convince me that you've found two national timing labs with 1) state-of-the-art optical clocks, 2) which operate as phase (time) standards instead of as frequency standards, 3) or run continuously for a year (instead of a few times per week), 4) are connected by stabilized fiber, 5) that cross plate boundaries moving anywhere near as much as 10 cm/year, and 6) the optical time nuts running the clocks don't already factor geodetic effects like this into their clock comparisons... Unfortunately I won't be able to measure this. Even if John Miles (who also lives near Seattle) and I find optical clocks on eBay some day, and we find a way to run 30 miles of fiber between us without anyone noticing, we are both on the same tectonic plate so the drift cancels out. Note that lunar/solar tidal effects would be common mode to us as well. /tvb [1] https://pnsn.org/outreach/about-earthquakes/plate-tectonics https://www.eoas.ubc.ca/courses/eosc256/jan26_plates_rebound.pdf [2] https://arxiv.org/ftp/arxiv/papers/1309/1309.1137.pdf https://arxiv.org/ftp/arxiv/papers/1704/1704.06323.pdf http://jilawww.colorado.edu/yelabs/sites/default/files/uploads/Sr%20best%20clock_Bloom_Nature.pdf ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Frequency over fiber (was WWV and legal issues)
Hi > On Sep 2, 2018, at 7:17 AM, Magnus Danielson > wrote: > > Hi Gerhard, > > I see that this became a separate thread. > > On 09/02/2018 01:38 AM, Gerhard Hoffmann wrote: >> >> >> Am 01.09.2018 um 20:40 schrieb Magnus Danielson: >>> One should first know that there is a lot of papers now on frequency >>> transfer over fiber. The stability achieved on the best ones so far >>> greatly below that of the optical clocks that they want to compare. >> >> Please, in a nutshell: what are the worst offenders: >> >> - tranceivers (mechanical, temp, other misfeatures) >> - cables ( bending, temp, mechanical stress) >> - others? >> >> In the case of transceivers: are there desirable modifications >> that would alleviate the problems? > > Acoustical sensitivity, low frequency changes. > > For optical clocks and frequency transfer, just the vibration from > traffic and other activity causes disturbances which disturbes the group > delay. What is done for these links is to actively compensate then using > a return path and closing the loop with a controller, very much like a > PLL. The length of the loop limits the bandwidth and hence how high up > the compensation can be done, so for longer stretches, this needs to be > repeated. They have now built links from PTB to SYRTE and NPL. > > Temperature shifts are slower, but also compensated though the active loop. I suspect there’s a longer list of “slow” environmental effects that are also taken care of with the compensation setup. One would guess that crossing a active fault line would be “interesting”. Bob > > Close proximity to strong power-currents have also been shown to cause > modulations, so separate from power-cables if you can. > > Remember that the end nodes have very stable clocks, so their effects > can be taken out of the equation. For other setups, such as telco > operation, that's a completely different ballgame. > > Cheers, > Magnus > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Frequency over fiber (was WWV and legal issues)
Hi Gerhard, I see that this became a separate thread. On 09/02/2018 01:38 AM, Gerhard Hoffmann wrote: > > > Am 01.09.2018 um 20:40 schrieb Magnus Danielson: >> One should first know that there is a lot of papers now on frequency >> transfer over fiber. The stability achieved on the best ones so far >> greatly below that of the optical clocks that they want to compare. > > Please, in a nutshell: what are the worst offenders: > > - tranceivers (mechanical, temp, other misfeatures) > - cables ( bending, temp, mechanical stress) > - others? > > In the case of transceivers: are there desirable modifications > that would alleviate the problems? Acoustical sensitivity, low frequency changes. For optical clocks and frequency transfer, just the vibration from traffic and other activity causes disturbances which disturbes the group delay. What is done for these links is to actively compensate then using a return path and closing the loop with a controller, very much like a PLL. The length of the loop limits the bandwidth and hence how high up the compensation can be done, so for longer stretches, this needs to be repeated. They have now built links from PTB to SYRTE and NPL. Temperature shifts are slower, but also compensated though the active loop. Close proximity to strong power-currents have also been shown to cause modulations, so separate from power-cables if you can. Remember that the end nodes have very stable clocks, so their effects can be taken out of the equation. For other setups, such as telco operation, that's a completely different ballgame. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
