Don't over-interpret the 50 Hz aspect, I don't remember those details
from 4.5 months back or so, as I already indicated. I can ask on the
details tomorrow. I think they discussed the Kerr effect:
https://en.wikipedia.org/wiki/Kerr_effect
The PTB folks asked me the same question essentially.
Would be nice to verify it.
Cheers,
Magnus
On 08/24/2016 12:11 AM, David wrote:
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
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