Optical link connects atomic clocks over 1400 km of fibre
Some interesting developments in european atomic clocks.
http://www.nature.com/articles/ncomms12443
The time kept by atomic clocks in France and Germany has been compared
for the first time using a new 1400 km optical-fibre link between labs
in Paris and Braunschweig. Hailed as the first comparison of its kind
made across an international border, the link has already shown that
two of the most precise optical atomic clocks in Europe agree to
within 5 × 10–17. The link is the first step towards a European
network of optical clocks that will provide extremely stable and
precise time signals for research in a number of scientific fields
including fundamental physics, astrophysics and geosciences.
An optical atomic clock works by keeping a laser in resonance with an
electronic transition between energy levels in an atom or ion – with
the "ticks" of the clock being the frequency of the laser light. As
with any clock, it is important to be able to compare the frequencies
of two or more instruments to ensure that they are working as
expected. Comparisons are also important for basic research,
particularly for testing the fundamental physical laws and constants
that are involved in the operation of atomic clocks.
Both of the clocks are based on the same optical transition in
strontium atoms, which are held in optical lattices created by laser
light. The clock at the LNE-SYRTE laboratory in Paris operates at an
uncertainty of about 4.1 × 10–17 and the clock at the PTB Braunschweig
laboratory at 1.8 × 10–17.
Gravitational shift
If they were side by side, the clocks would tick at exactly the same
frequency. However, there is a 25 m difference in the elevation
between the two locations, which means that the Earth's gravitational
field is not the same for both clocks – causing them to tick at
slightly different frequencies. This gravitational redshift was
confirmed by the link, which can detect differences in elevation as
small as 5 m.
The link comprises two commercial-grade optical fibres that run
between Paris and Braunschweig. The route is not the shortest distance
between the two clocks, but rather takes a significant southward
detour via Strasbourg on the French–German border. For every 1020
photons that begin the journey, only one would arrive at its
destination. This 200 dB attenuation is compensated for by 10 or so
special amplifiers along the route. The German portion of the link
runs 710 km from Braunschweig to Strasbourg and is dedicated to
connecting the clocks. The French portion, however, uses 705 km of an
active telecommunications link that also carries Internet traffic. As
a result, two different approaches were needed to amplify the clock
signals on either side of the border.
Second connection
The optical clock at PTB Braunschweig is already linked to the Max
Planck Institute for Quantum Optics (MPQ) in Garching near Munich.
This is done via a 920 km pair of optical fibres, and researchers at
the MPQ plan to use the clock signal to make extremely precise
spectroscopy measurements. A further expansion of this network would
provide researchers in other labs in Europe with access to
high-precision clock signals.
Applications could include measuring a fundamental physics constant in
several different locations – to confirm that the value of the
constant is indeed constant. Other possible uses include precision
measurements in spectroscopy that look for evidence of physics beyond
the Standard Model and making very precise measurements of the shape
and density of the Earth.
The construction and testing of the link are described in Nature Communications.
About the author
Hamish Johnston is editor of physicsworld.com
The presentations and posters at 8FSM and EFTF York have been
interesting. The PTB link-end is even more stable than the clock, but
only in frequency stability.
More links is planned, among those between LNE-SYRTE at Paris
Observatory and NPL outside London. Such links aid in the comparison of
optical clocks, alongside the PTB portable optical clock, as various
realizations of same and different species is realized by various labs.
The inter-comparations will be important to narrow down the frequency
relationships as well as iron out various systematic shifts of
implementations. In the end, this is important as stepping stones
towards the redefinition of the SI second in terms of optical clocks.
The active damping being done is quite interesting, but the bandwidth
allowed is limited by the length of the span due to the time-delay, so
that makes the length of each span limited and inter-related to the
bandwidth of compensation.
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.
Fascinating stuff, and that they now can tie together labs for real is a
real advancement. Many labs is doing it, and they have different approaches.
Cheers,
Magnus
On 08/23/2016 01:04 AM, André Esteves wrote:
Some interesting developments in european atomic clocks.
http://www.nature.com/articles/ncomms12443
The time kept by atomic clocks in France and Germany has been compared
for the first time using a new 1400 km optical-fibre link between labs
in Paris and Braunschweig. Hailed as the first comparison of its kind
made across an international border, the link has already shown that
two of the most precise optical atomic clocks in Europe agree to
within 5 × 10–17. The link is the first step towards a European
network of optical clocks that will provide extremely stable and
precise time signals for research in a number of scientific fields
including fundamental physics, astrophysics and geosciences.
An optical atomic clock works by keeping a laser in resonance with an
electronic transition between energy levels in an atom or ion – with
the "ticks" of the clock being the frequency of the laser light. As
with any clock, it is important to be able to compare the frequencies
of two or more instruments to ensure that they are working as
expected. Comparisons are also important for basic research,
particularly for testing the fundamental physical laws and constants
that are involved in the operation of atomic clocks.
Both of the clocks are based on the same optical transition in
strontium atoms, which are held in optical lattices created by laser
light. The clock at the LNE-SYRTE laboratory in Paris operates at an
uncertainty of about 4.1 × 10–17 and the clock at the PTB Braunschweig
laboratory at 1.8 × 10–17.
Gravitational shift
If they were side by side, the clocks would tick at exactly the same
frequency. However, there is a 25 m difference in the elevation
between the two locations, which means that the Earth's gravitational
field is not the same for both clocks – causing them to tick at
slightly different frequencies. This gravitational redshift was
confirmed by the link, which can detect differences in elevation as
small as 5 m.
The link comprises two commercial-grade optical fibres that run
between Paris and Braunschweig. The route is not the shortest distance
between the two clocks, but rather takes a significant southward
detour via Strasbourg on the French–German border. For every 1020
photons that begin the journey, only one would arrive at its
destination. This 200 dB attenuation is compensated for by 10 or so
special amplifiers along the route. The German portion of the link
runs 710 km from Braunschweig to Strasbourg and is dedicated to
connecting the clocks. The French portion, however, uses 705 km of an
active telecommunications link that also carries Internet traffic. As
a result, two different approaches were needed to amplify the clock
signals on either side of the border.
Second connection
The optical clock at PTB Braunschweig is already linked to the Max
Planck Institute for Quantum Optics (MPQ) in Garching near Munich.
This is done via a 920 km pair of optical fibres, and researchers at
the MPQ plan to use the clock signal to make extremely precise
spectroscopy measurements. A further expansion of this network would
provide researchers in other labs in Europe with access to
high-precision clock signals.
Applications could include measuring a fundamental physics constant in
several different locations – to confirm that the value of the
constant is indeed constant. Other possible uses include precision
measurements in spectroscopy that look for evidence of physics beyond
the Standard Model and making very precise measurements of the shape
and density of the Earth.
The construction and testing of the link are described in Nature Communications.
About the author
Hamish Johnston is editor of physicsworld.com
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.
What is the coupling mechanism giving rise to the 50Hz disturbance?
DaveB, NZ
----- Original Message -----
From: "Magnus Danielson" magnus@rubidium.dyndns.org
To: time-nuts@febo.com
Cc: magnus@rubidium.se
Sent: Wednesday, August 24, 2016 8:54 AM
Subject: Re: [time-nuts] Optical link connects atomic clocks over 1400 km of
fibre
The presentations and posters at 8FSM and EFTF York have been interesting.
The PTB link-end is even more stable than the clock, but only in frequency
stability.
More links is planned, among those between LNE-SYRTE at Paris Observatory
and NPL outside London. Such links aid in the comparison of optical
clocks, alongside the PTB portable optical clock, as various realizations
of same and different species is realized by various labs. The
inter-comparations will be important to narrow down the frequency
relationships as well as iron out various systematic shifts of
implementations. In the end, this is important as stepping stones towards
the redefinition of the SI second in terms of optical clocks.
The active damping being done is quite interesting, but the bandwidth
allowed is limited by the length of the span due to the time-delay, so
that makes the length of each span limited and inter-related to the
bandwidth of compensation.
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.
Fascinating stuff, and that they now can tie together labs for real is a
real advancement. Many labs is doing it, and they have different
approaches.
Cheers,
Magnus
On 08/23/2016 01:04 AM, André Esteves wrote:
Some interesting developments in european atomic clocks.
http://www.nature.com/articles/ncomms12443
The time kept by atomic clocks in France and Germany has been compared
for the first time using a new 1400 km optical-fibre link between labs
in Paris and Braunschweig. Hailed as the first comparison of its kind
made across an international border, the link has already shown that
two of the most precise optical atomic clocks in Europe agree to
within 5 × 10–17. The link is the first step towards a European
network of optical clocks that will provide extremely stable and
precise time signals for research in a number of scientific fields
including fundamental physics, astrophysics and geosciences.
An optical atomic clock works by keeping a laser in resonance with an
electronic transition between energy levels in an atom or ion – with
the "ticks" of the clock being the frequency of the laser light. As
with any clock, it is important to be able to compare the frequencies
of two or more instruments to ensure that they are working as
expected. Comparisons are also important for basic research,
particularly for testing the fundamental physical laws and constants
that are involved in the operation of atomic clocks.
Both of the clocks are based on the same optical transition in
strontium atoms, which are held in optical lattices created by laser
light. The clock at the LNE-SYRTE laboratory in Paris operates at an
uncertainty of about 4.1 × 10–17 and the clock at the PTB Braunschweig
laboratory at 1.8 × 10–17.
Gravitational shift
If they were side by side, the clocks would tick at exactly the same
frequency. However, there is a 25 m difference in the elevation
between the two locations, which means that the Earth's gravitational
field is not the same for both clocks – causing them to tick at
slightly different frequencies. This gravitational redshift was
confirmed by the link, which can detect differences in elevation as
small as 5 m.
The link comprises two commercial-grade optical fibres that run
between Paris and Braunschweig. The route is not the shortest distance
between the two clocks, but rather takes a significant southward
detour via Strasbourg on the French–German border. For every 1020
photons that begin the journey, only one would arrive at its
destination. This 200 dB attenuation is compensated for by 10 or so
special amplifiers along the route. The German portion of the link
runs 710 km from Braunschweig to Strasbourg and is dedicated to
connecting the clocks. The French portion, however, uses 705 km of an
active telecommunications link that also carries Internet traffic. As
a result, two different approaches were needed to amplify the clock
signals on either side of the border.
Second connection
The optical clock at PTB Braunschweig is already linked to the Max
Planck Institute for Quantum Optics (MPQ) in Garching near Munich.
This is done via a 920 km pair of optical fibres, and researchers at
the MPQ plan to use the clock signal to make extremely precise
spectroscopy measurements. A further expansion of this network would
provide researchers in other labs in Europe with access to
high-precision clock signals.
Applications could include measuring a fundamental physics constant in
several different locations – to confirm that the value of the
constant is indeed constant. Other possible uses include precision
measurements in spectroscopy that look for evidence of physics beyond
the Standard Model and making very precise measurements of the shape
and density of the Earth.
The construction and testing of the link are described in Nature
Communications.
About the author
Hamish Johnston is editor of physicsworld.com
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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To unsubscribe, go to
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and follow the instructions there.
I think they speculated in the Kerr effect, so that the voltage swings
would modulate the fiber. I don't consider it verified, so I do not take
cross-examination on it. I can ask thought.
Cheers,
Magnus
On 08/23/2016 11:31 PM, Dave Brown wrote:
What is the coupling mechanism giving rise to the 50Hz disturbance?
DaveB, NZ
----- Original Message ----- From: "Magnus Danielson"
magnus@rubidium.dyndns.org
To: time-nuts@febo.com
Cc: magnus@rubidium.se
Sent: Wednesday, August 24, 2016 8:54 AM
Subject: Re: [time-nuts] Optical link connects atomic clocks over 1400
km of fibre
The presentations and posters at 8FSM and EFTF York have been
interesting. The PTB link-end is even more stable than the clock, but
only in frequency stability.
More links is planned, among those between LNE-SYRTE at Paris
Observatory and NPL outside London. Such links aid in the comparison
of optical clocks, alongside the PTB portable optical clock, as
various realizations of same and different species is realized by
various labs. The inter-comparations will be important to narrow down
the frequency relationships as well as iron out various systematic
shifts of implementations. In the end, this is important as stepping
stones towards the redefinition of the SI second in terms of optical
clocks.
The active damping being done is quite interesting, but the bandwidth
allowed is limited by the length of the span due to the time-delay, so
that makes the length of each span limited and inter-related to the
bandwidth of compensation.
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.
Fascinating stuff, and that they now can tie together labs for real is
a real advancement. Many labs is doing it, and they have different
approaches.
Cheers,
Magnus
On 08/23/2016 01:04 AM, André Esteves wrote:
Some interesting developments in european atomic clocks.
http://www.nature.com/articles/ncomms12443
The time kept by atomic clocks in France and Germany has been compared
for the first time using a new 1400 km optical-fibre link between labs
in Paris and Braunschweig. Hailed as the first comparison of its kind
made across an international border, the link has already shown that
two of the most precise optical atomic clocks in Europe agree to
within 5 × 10–17. The link is the first step towards a European
network of optical clocks that will provide extremely stable and
precise time signals for research in a number of scientific fields
including fundamental physics, astrophysics and geosciences.
An optical atomic clock works by keeping a laser in resonance with an
electronic transition between energy levels in an atom or ion – with
the "ticks" of the clock being the frequency of the laser light. As
with any clock, it is important to be able to compare the frequencies
of two or more instruments to ensure that they are working as
expected. Comparisons are also important for basic research,
particularly for testing the fundamental physical laws and constants
that are involved in the operation of atomic clocks.
Both of the clocks are based on the same optical transition in
strontium atoms, which are held in optical lattices created by laser
light. The clock at the LNE-SYRTE laboratory in Paris operates at an
uncertainty of about 4.1 × 10–17 and the clock at the PTB Braunschweig
laboratory at 1.8 × 10–17.
Gravitational shift
If they were side by side, the clocks would tick at exactly the same
frequency. However, there is a 25 m difference in the elevation
between the two locations, which means that the Earth's gravitational
field is not the same for both clocks – causing them to tick at
slightly different frequencies. This gravitational redshift was
confirmed by the link, which can detect differences in elevation as
small as 5 m.
The link comprises two commercial-grade optical fibres that run
between Paris and Braunschweig. The route is not the shortest distance
between the two clocks, but rather takes a significant southward
detour via Strasbourg on the French–German border. For every 1020
photons that begin the journey, only one would arrive at its
destination. This 200 dB attenuation is compensated for by 10 or so
special amplifiers along the route. The German portion of the link
runs 710 km from Braunschweig to Strasbourg and is dedicated to
connecting the clocks. The French portion, however, uses 705 km of an
active telecommunications link that also carries Internet traffic. As
a result, two different approaches were needed to amplify the clock
signals on either side of the border.
Second connection
The optical clock at PTB Braunschweig is already linked to the Max
Planck Institute for Quantum Optics (MPQ) in Garching near Munich.
This is done via a 920 km pair of optical fibres, and researchers at
the MPQ plan to use the clock signal to make extremely precise
spectroscopy measurements. A further expansion of this network would
provide researchers in other labs in Europe with access to
high-precision clock signals.
Applications could include measuring a fundamental physics constant in
several different locations – to confirm that the value of the
constant is indeed constant. Other possible uses include precision
measurements in spectroscopy that look for evidence of physics beyond
the Standard Model and making very precise measurements of the shape
and density of the Earth.
The construction and testing of the link are described in Nature
Communications.
About the author
Hamish Johnston is editor of physicsworld.com
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.
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To unsubscribe, go to
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and follow the instructions there.
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" magnus@rubidium.dyndns.org
To: time-nuts@febo.com
Cc: magnus@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
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" magnus@rubidium.dyndns.org
To: time-nuts@febo.com
Cc: magnus@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.
Hi
I would not rule out line noise into the electronic side of things.
Bob
On Aug 23, 2016, at 7:06 PM, Magnus Danielson magnus@rubidium.dyndns.org wrote:
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" magnus@rubidium.dyndns.org
To: time-nuts@febo.com
Cc: magnus@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.
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.
The Kerr effect is Proportional to the square of the field so one would
expect a strong 100Hz component from this.
The magneto optical Kerr eefect which rotates the plane of polarisation is
linear however.
Bruce
On Wednesday, August 24, 2016 07:04:31 AM Bob kb8tq wrote:
Hi
I would not rule out line noise into the electronic side of things.
Bob
On Aug 23, 2016, at 7:06 PM, Magnus Danielson
wrote:
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" magnus@rubidium.dyndns.org
To: time-nuts@febo.com
Cc: magnus@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
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instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
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instructions there.
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To unsubscribe, go to
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instructions there.
So the way to eliminate that perturbation would be to put a copper
jacket over it to attenuate the EM field?
André Esteves
2016-08-25 0:33 GMT+01:00 Bruce Griffiths bruce.griffiths@xtra.co.nz:
The Kerr effect is Proportional to the square of the field so one would
expect a strong 100Hz component from this.
The magneto optical Kerr eefect which rotates the plane of polarisation is
linear however.
Bruce
On Wednesday, August 24, 2016 07:04:31 AM Bob kb8tq wrote:
Hi
I would not rule out line noise into the electronic side of things.
Bob
On Aug 23, 2016, at 7:06 PM, Magnus Danielson
wrote:
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" magnus@rubidium.dyndns.org
To: time-nuts@febo.com
Cc: magnus@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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You'd need a rather thick copper jacket to shield effectively against the 50Hz magnetic field.
Bruce
On Thursday, 25 August 2016 3:00 PM, André Esteves <aifesteves@gmail.com> wrote:
So the way to eliminate that perturbation would be to put a copper
jacket over it to attenuate the EM field?
André Esteves
2016-08-25 0:33 GMT+01:00 Bruce Griffiths bruce.griffiths@xtra.co.nz:
The Kerr effect is Proportional to the square of the field so one would
expect a strong 100Hz component from this.
The magneto optical Kerr eefect which rotates the plane of polarisation is
linear however.
Bruce
On Wednesday, August 24, 2016 07:04:31 AM Bob kb8tq wrote:
Hi
I would not rule out line noise into the electronic side of things.
Bob
On Aug 23, 2016, at 7:06 PM, Magnus Danielson
wrote:
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" magnus@rubidium.dyndns.org
To: time-nuts@febo.com
Cc: magnus@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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From: Bruce Griffiths
You'd need a rather thick copper jacket to shield effectively against the
50Hz magnetic field.
Bruce
Would mu-metal be any use?
https://en.wikipedia.org/wiki/Mu-metal
http://mumetal.co.uk/
Cheers,
David
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv
As long as you don't saturate it, bend it, hit it or drop it. Depending on the ambient field a multilayer shield with outer layers of high saturation magnetic material may be required.
Bruce
On Thursday, 25 August 2016 7:02 PM, David J Taylor <david-taylor@blueyonder.co.uk> wrote:
From: Bruce Griffiths
You'd need a rather thick copper jacket to shield effectively against the
50Hz magnetic field.
Bruce
Would mu-metal be any use?
https://en.wikipedia.org/wiki/Mu-metal
http://mumetal.co.uk/
Cheers,
David
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv
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Bruce wrote:
As long as you don't saturate it, bend it, hit it or drop it.
And that is AFTER you form it to shape and then anneal it in a Hydrogen
atmosphere.
You may (probably would) need several layers, perhaps of different
high-permeability alloys, with a thick outermost layer of soft iron.
Best regards,
Charles
In message 1057836989.2088307.1472104857885.JavaMail.yahoo@mail.yahoo.com, Br
uce Griffiths writes:
You'd need a rather thick copper jacket to shield effectively
against the 50Hz magnetic field.
As in: A good-sized fraction of the wavelength if I recall :-)
Electric fields are so much easier...
One interesting thing here is that across distances like this,
there would be significant longitudal currents in such a shield.
Not as bad as metal spanning the Mississippi, but getting there.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
On 25/08/16 18:25, Poul-Henning Kamp wrote:
In message 1057836989.2088307.1472104857885.JavaMail.yahoo@mail.yahoo.com, Br
uce Griffiths writes:
You'd need a rather thick copper jacket to shield effectively
against the 50Hz magnetic field.
As in: A good-sized fraction of the wavelength if I recall :-)
Electric fields are so much easier...
One interesting thing here is that across distances like this,
there would be significant longitudal currents in such a shield.
Not as bad as metal spanning the Mississippi, but getting there.
Skin depth is probably a good place to start with in roughly estimating
the thickness needed. In copper at 50 Hz, a quick calculation suggests
9.5 mm, but this just the depth at which the E-M field decreases by 1/e
or 8.7 dB. Thus to get 20 dB attenuation this implies a thickness of
about 22 mm, etc.
Hi
There is also the minor issue of putting the (very thick) layers on in a spiral around the "core". You put one layer on clockwise and the next counter clockwise. Since the materials are quite springy, controlling the whole process through heat treating is a real chore.
Bob
On Aug 25, 2016, at 4:25 AM, Poul-Henning Kamp phk@phk.freebsd.dk wrote:
In message 1057836989.2088307.1472104857885.JavaMail.yahoo@mail.yahoo.com, Br
uce Griffiths writes:
You'd need a rather thick copper jacket to shield effectively
against the 50Hz magnetic field.
As in: A good-sized fraction of the wavelength if I recall :-)
Electric fields are so much easier...
One interesting thing here is that across distances like this,
there would be significant longitudal currents in such a shield.
Not as bad as metal spanning the Mississippi, but getting there.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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.
Hi,
On 08/25/2016 11:04 AM, Bill Metzenthen wrote:
On 25/08/16 18:25, Poul-Henning Kamp wrote:
In message
1057836989.2088307.1472104857885.JavaMail.yahoo@mail.yahoo.com, Br
uce Griffiths writes:
You'd need a rather thick copper jacket to shield effectively
against the 50Hz magnetic field.
As in: A good-sized fraction of the wavelength if I recall :-)
Electric fields are so much easier...
One interesting thing here is that across distances like this,
there would be significant longitudal currents in such a shield.
Not as bad as metal spanning the Mississippi, but getting there.
Skin depth is probably a good place to start with in roughly estimating
the thickness needed. In copper at 50 Hz, a quick calculation suggests
9.5 mm, but this just the depth at which the E-M field decreases by 1/e
or 8.7 dB. Thus to get 20 dB attenuation this implies a thickness of
about 22 mm, etc.
While interesting, I think you are going overboard. The easy remedy is
to move the fiber of the power-cable and put it on some distance, just
choose a different path for it in the building.
Cheers,
Magnus
to shield against DC and low frequency magnetic field usually high
permeability magnetizable material -- Permalloy, Mu-metal or similar is
used, the field concentrates in the high permeability material and
"behind it" is no left over magnetic field
73
Alex
On 8/25/2016 11:10 AM, Magnus Danielson wrote:
Hi,
On 08/25/2016 11:04 AM, Bill Metzenthen wrote:
On 25/08/16 18:25, Poul-Henning Kamp wrote:
In message
1057836989.2088307.1472104857885.JavaMail.yahoo@mail.yahoo.com, Br
uce Griffiths writes:
You'd need a rather thick copper jacket to shield effectively
against the 50Hz magnetic field.
As in: A good-sized fraction of the wavelength if I recall :-)
Electric fields are so much easier...
One interesting thing here is that across distances like this,
there would be significant longitudal currents in such a shield.
Not as bad as metal spanning the Mississippi, but getting there.
Skin depth is probably a good place to start with in roughly estimating
the thickness needed. In copper at 50 Hz, a quick calculation suggests
9.5 mm, but this just the depth at which the E-M field decreases by 1/e
or 8.7 dB. Thus to get 20 dB attenuation this implies a thickness of
about 22 mm, etc.
While interesting, I think you are going overboard. The easy remedy is
to move the fiber of the power-cable and put it on some distance, just
choose a different path for it in the building.
Cheers,
Magnus
time-nuts mailing list -- time-nuts@febo.com
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No virus found in this message.
Checked by AVG - www.avg.com
Version: 2016.0.7752 / Virus Database: 4647/12877 - Release Date:
08/25/16
Let's know if they get to the bottom of this, Magnus- its interesting to
speculate on the cause but hopefully they figure out the real issue.
DaveB, NZ
----- Original Message -----
From: "Magnus Danielson" magnus@rubidium.dyndns.org
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Cc: magnus@rubidium.se
Sent: Wednesday, August 24, 2016 11:06 AM
Subject: Re: [time-nuts] Optical link connects atomic clocks over 1400 km of
fibre
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" magnus@rubidium.dyndns.org
To: time-nuts@febo.com
Cc: magnus@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
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