[time-nuts] Frequency over fiber (was WWV and legal issues)

Peter Vince petervince1952 at gmail.com
Sun Sep 2 16:13:05 EDT 2018


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 <magnus at 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
>


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