[time-nuts] Frequency over fiber (was WWV and legal issues)
petervince1952 at gmail.com
Sun Sep 2 16:13:05 EDT 2018
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?
On 2 September 2018 at 12:17, Magnus Danielson <magnus at rubidium.dyndns.org>
> 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.
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