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 <petervince1...@gmail.com> 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 <mag...@rubidium.dyndns.org > > > 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.