I could not find it in the links but Magnus mentions 50 Hz instead of 100 Hz.
I would expect a 100 Hz noise signal if it was vibration coupled from magnetostriction in a transformer; magnetostrictive strain depends on the magnitude of the magnetic field strength and not the sign which is why 50/60 Hz transformers hum at 100/120 Hz. 50 Hz however fits with piezomagnetism if the optical fiber was in an oscillating magnetic field and antiferromagnetic; for piezomagnetism, the strain does follow the sign. https://en.wikipedia.org/wiki/Magnetostriction https://en.wikipedia.org/wiki/Piezomagnetism I do not know if optical fibers are even slightly antiferromagnetic but maybe doping can make them susceptible? On Wed, 24 Aug 2016 09:31:57 +1200, you wrote: >What is the coupling mechanism giving rise to the 50Hz disturbance? >DaveB, NZ > >----- Original Message ----- >From: "Magnus Danielson" <mag...@rubidium.dyndns.org> >To: <time-nuts@febo.com> >Cc: <mag...@rubidium.se> >Sent: Wednesday, August 24, 2016 8:54 AM >Subject: Re: [time-nuts] Optical link connects atomic clocks over 1400 km of >fibre > >> ... >> >> These links is in principle not very complex, but they are regardless >> somewhat sensitive. One link experienced excessive 50 Hz disturbance, >> which they could trace to the fact that for a short distance the fibre was >> laying alongside the house 400V three-phase feed-cable with quite a bit of >> current in it. >> >> ... >> >> Cheers, >> Magnus _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.