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.