Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[jimlux]

On 8/25/16 8:12 PM, Bill Metzenthen wrote:

On 26/08/16 08:14, Hal Murray wrote:

billm...@gmail.com said:

If the conductor also has magnetic properties (e.g. if iron were
used)  then
magnetic saturation could be an issue.

Ah...  Sorry I wasn't clear.  How about

Is skin depth an interesting concept if you are using materials
commonly used
for magnetic shielding, for example mu-metal?

The electrical conduction is poor so the normal skin depth reasoning
probably
won't be useful in practical examples.



For skin depth, the lower conductivity of mu-metal is more than
compensated for by its higher permeability.  At 50 Hz its skin depth is
calculated to be around 0.3 mm assuming that the conductivity and
permeability are real (as distinct from complex) and everything is
linear.  I haven't needed to consider what happens when these
assumptions aren't valid so I could only guess how rapidly the skin
depth increases when a magnetic material such as mu-metal is pushed past
its linear region.

The usual skin depth calculation is based upon assumptions about the
form of the electromagnetic field and the conductor, which might not
apply to the situation in which one is interested. Despite this, it is
often used to get an estimate which is useful in a range of applications.



it's all about sqrt( rho/mu)... good conductivity and high mu are what 
you want.  soft iron works well... heck, steel works well for a lot of 
applications.


Mu metal (which as others have noted has all sorts of handling and 
fabrication issues) is for the more exotic cases..


But, could you not run a differential pair of fibers, and both would be 
affected, but with opposite signs



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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Bill Metzenthen]

On 26/08/16 08:14, Hal Murray wrote:

billm...@gmail.com said:

If the conductor also has magnetic properties (e.g. if iron were used)  then
magnetic saturation could be an issue.

Ah...  Sorry I wasn't clear.  How about

Is skin depth an interesting concept if you are using materials commonly used
for magnetic shielding, for example mu-metal?

The electrical conduction is poor so the normal skin depth reasoning probably
won't be useful in practical examples.


For skin depth, the lower conductivity of mu-metal is more than 
compensated for by its higher permeability.  At 50 Hz its skin depth is 
calculated to be around 0.3 mm assuming that the conductivity and 
permeability are real (as distinct from complex) and everything is 
linear.  I haven't needed to consider what happens when these 
assumptions aren't valid so I could only guess how rapidly the skin 
depth increases when a magnetic material such as mu-metal is pushed past 
its linear region.


The usual skin depth calculation is based upon assumptions about the 
form of the electromagnetic field and the conductor, which might not 
apply to the situation in which one is interested. Despite this, it is 
often used to get an estimate which is useful in a range of applications.



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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Dave Brown]

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" <mag...@rubidium.dyndns.org>
To: "Discussion of precise time and frequency measurement" 
<time-nuts@febo.com>

Cc: <mag...@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" <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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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Alex Pummer]

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.ya...@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
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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


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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Hal Murray]

billm...@gmail.com said:
> If the conductor also has magnetic properties (e.g. if iron were used)  then
> magnetic saturation could be an issue. 

Ah...  Sorry I wasn't clear.  How about

Is skin depth an interesting concept if you are using materials commonly used 
for magnetic shielding, for example mu-metal?

The electrical conduction is poor so the normal skin depth reasoning probably 
won't be useful in practical examples.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Bill Metzenthen]

On 26/08/16 06:33, Hal Murray wrote:

billm...@gmail.com said:

Skin depth is probably a good place to start with in roughly estimating  the
thickness needed.  In copper at 50 Hz, ...

Is skin depth an appropriate concept for magnetic shielding?  Or does it get
messed up by saturation?



Skin depth is appropriate for an electromagnetic field.  It doesn't 
apply for a static electric or magnetic field but does apply for a 
varying magnetic field.  Without going into the details of 
electromagnetic field theory, the mechanism is that the varying magnetic 
field induces a current in the conductor (copper under consideration 
here) and that this current in turn produces a magnetic field which 
opposes the original magnetic field. Strictly magnetic effects, e.g. 
ferromagnetism, play no part in this scenario and hence saturation is 
not an issue.


If the conductor also has magnetic properties (e.g. if iron were used) 
then magnetic saturation could be an issue.



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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Hal Murray]

billm...@gmail.com said:
> Skin depth is probably a good place to start with in roughly estimating  the
> thickness needed.  In copper at 50 Hz, ...

Is skin depth an appropriate concept for magnetic shielding?  Or does it get 
messed up by saturation?



-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Magnus Danielson]

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.ya...@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
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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Bill Metzenthen]

On 25/08/16 18:25, Poul-Henning Kamp wrote:


In message <1057836989.2088307.1472104857885.javamail.ya...@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.



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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Bob kb8tq]

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  wrote:
> 
> 
> In message <1057836989.2088307.1472104857885.javamail.ya...@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
> p...@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.
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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Charles Steinmetz]

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


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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Poul-Henning Kamp]

In message <1057836989.2088307.1472104857885.javamail.ya...@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
p...@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.
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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Bruce Griffiths]

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 <aifeste...@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.griffi...@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
> <mag...@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" <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
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>> >> instructions there.
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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[André Esteves]

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.griffi...@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
> <mag...@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" <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.
>> >
>> > ___
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>> > instructions there.
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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Bruce Griffiths]

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 
<mag...@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" <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.
> > 
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> > instructions there.
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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Bob kb8tq]

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 <mag...@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" <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.
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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Magnus Danielson]

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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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[David]

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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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Magnus Danielson]

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"
<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



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://physicsworld.com/cws/article/news/2016/aug/22/optical-link-connects-atomic-clocks-over-1400-nbsp-km-of-fibre


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 Braunschwe

Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Hal Murray]

tract...@ihug.co.nz said:
> What is the coupling mechanism giving rise to the 50Hz disturbance? 

My guess would be mechanical.  Maybe from a nearby transformer.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Dave Brown]

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



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://physicsworld.com/cws/article/news/2016/aug/22/optical-link-connects-atomic-clocks-over-1400-nbsp-km-of-fibre

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 extre

Re: [time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[Magnus Danielson]

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://physicsworld.com/cws/article/news/2016/aug/22/optical-link-connects-atomic-clocks-over-1400-nbsp-km-of-fibre

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 

[time-nuts] Optical link connects atomic clocks over 1400 km of fibre

[André Esteves]

Some interesting developments in european atomic clocks.

http://physicsworld.com/cws/article/news/2016/aug/22/optical-link-connects-atomic-clocks-over-1400-nbsp-km-of-fibre

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
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