Re: [time-nuts] Optical transfer of time and frequency

[Michael Wouters]

Not stable enough unfortunately. An ageing rate of a few parts in 10^12 per
day is typical, which translates to 100 ns. You could be brave and model
that as linear frequency drift to predict the time offset to the required
0.5 ns or so but I suspect that it could be a very frustrating exercise. We
operate a large number of rubidiums and sudden changes in frequency are
quite common.

Cheers
Michael.

On Thursday, 5 May 2016, Hal Murray  wrote:

>
> t...@leapsecond.com said:
> > Any of these methods is going to be a challenge, given their 500 ps
> > requirement and their $2k budget.
>
> How stable are surplus rubidium oscillators?
>
> How close could you get if you brought two of them together, compared
> phase,
> drove them to the site for a nights work, drove them back to the same
> location and compared the phase again.
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
> ___
> 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.

Re: [time-nuts] Optical transfer of time and frequency

[Ilia Platone]

I found only preliminary data about these transceivers.

I was meaning for a <2000€ overall solution, does a White Rabbit 
implementation fill this requisite ( I couldn't find much information 
about its costs)?


Also consider that nodes could be more than three also.

Ilia.


Il 30/04/2016 12:27, Bruce Griffiths ha scritto:

There are synchronous free space optical gigabit ethernet links available, it 
shouldn't take too much to modify one for White Rabbit.
Bruce
  


 On Saturday, 30 April 2016 10:13 PM, Magnus Danielson 
 wrote:
  


  Hi,

On 04/29/2016 11:45 PM, Michael Wouters wrote:

On Sat, Apr 30, 2016 at 6:14 AM, Magnus Danielson
 wrote:

Well, giving the conditions mentioned, doing ranging codes such as those
used by GPS is very easy and cheap. Doing this in bidirectional isn't too
hard. Doing a suitably high chip-rate should cost very little.

I've done two-way time-transfer over optical fibre using exactly this
technique. The TDEV is about 1 ps for tau>1s. Not so cheap, about 25K
euro per node (20K signal processing - NI FPGA, 2K laser and power
supplies, 1K detector, 1K RF electronics) in my setup, but that cost
could be greatly reduced since a $100 OEM FPGA could do the signal
processing (I've already done work on this but currently looking for
motivation to finish it off) and a simple, intensity-modulated laser
would probably be fine. A 2K euro budget would be a challenge though.

FPGA-wise, you need a very little FPGA resources.
If you consider the RedPitaya (200 USD) for instance, it is way beyond
what is needed.


The two-way time-transfer is relatively easy, but you will need to do some
calibration to get the precision needed.


At first glance, I would think that you should be able to define the
optical RX/TX path to within 10 cm without any trouble and that gives
you 300 ps accuracy. Even on fibre links, I don't think anyone would
claim an accuracy of better than a few hundred ps.

With a bit of calibration you can remove each nodes systematic asymmetry.

For optical fibers many does not even bother to do a pseudorandom
rangning. A repeating pattern suffice, such as that of SDH frames.

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.



--
Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999

___
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.

Re: [time-nuts] Optical transfer of time and frequency

[Bruce Griffiths]

There are synchronous free space optical gigabit ethernet links available, it 
shouldn't take too much to modify one for White Rabbit.
Bruce
 

On Saturday, 30 April 2016 10:13 PM, Magnus Danielson 
 wrote:
 

 Hi,

On 04/29/2016 11:45 PM, Michael Wouters wrote:
> On Sat, Apr 30, 2016 at 6:14 AM, Magnus Danielson
>  wrote:
>> Well, giving the conditions mentioned, doing ranging codes such as those
>> used by GPS is very easy and cheap. Doing this in bidirectional isn't too
>> hard. Doing a suitably high chip-rate should cost very little.
>
> I've done two-way time-transfer over optical fibre using exactly this
> technique. The TDEV is about 1 ps for tau>1s. Not so cheap, about 25K
> euro per node (20K signal processing - NI FPGA, 2K laser and power
> supplies, 1K detector, 1K RF electronics) in my setup, but that cost
> could be greatly reduced since a $100 OEM FPGA could do the signal
> processing (I've already done work on this but currently looking for
> motivation to finish it off) and a simple, intensity-modulated laser
> would probably be fine. A 2K euro budget would be a challenge though.

FPGA-wise, you need a very little FPGA resources.
If you consider the RedPitaya (200 USD) for instance, it is way beyond 
what is needed.

>> The two-way time-transfer is relatively easy, but you will need to do some
>> calibration to get the precision needed.
>>
>
> At first glance, I would think that you should be able to define the
> optical RX/TX path to within 10 cm without any trouble and that gives
> you 300 ps accuracy. Even on fibre links, I don't think anyone would
> claim an accuracy of better than a few hundred ps.

With a bit of calibration you can remove each nodes systematic asymmetry.

For optical fibers many does not even bother to do a pseudorandom 
rangning. A repeating pattern suffice, such as that of SDH frames.

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.

Re: [time-nuts] Optical transfer of time and frequency

[Javier Serrano]

On Sat, Apr 30, 2016 at 8:06 AM, Bruce Griffiths
 wrote:
> So far I haven't found an existing free space optical implementation of White 
> Rabbit.

There are two groups working on that subject that I know of:

Jean-Pierre Aubry [1] and his colleagues in EPFL (Neuchâtel campus, in
Switzerland). They started around one year ago.

Javier Díaz [2] in the University of Granada (Spain). Javier just
visited Neuchâtel with a PhD student (Paco Girela) who is supposed to
start working on free space WR soon, if I understood correctly.

Tell me off list if you would like me to connect you.

Cheers,

Javier

[1] https://people.epfl.ch/242679
[2] http://www.ugr.es/~jda/
___
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.

Re: [time-nuts] Optical transfer of time and frequency

[Magnus Danielson]

The free-space implementation of White Rabbit remains to be done.
If you can modulate optical GE over your optical links, then it should 
work out fairly well.


Actually, if you get that working, I'm sure they would enjoy seeing a 
paper on that in EFTF.


Cheers,
Magnus

On 04/30/2016 08:06 AM, Bruce Griffiths wrote:

White Rabbit would be good in that a suitable TDC design with 1ns resolution 
already exists for White Rabbit. This TDC is used in the Tunka valley (near 
lake Baikal) Siberian Cherenkov telescope array. Note this TDC uses the SERDES 
receiver in the FPGA to implement a serial to parallel converter with a 1GHz 
clock synthesised from the 125MHz White Rabbit clock.
So far I haven't found an existing free space optical implementation of White 
Rabbit.
Bruce


 On Saturday, 30 April 2016 11:00 AM, Michael Wouters 
 wrote:


  So why not do White Rabbit free space ?

Cheers
Michael

On Sat, Apr 30, 2016 at 4:04 AM, Paul Boven  wrote:

Hi everyone,

On 04/29/2016 03:28 PM, Magnus Danielson wrote:


Phase/time transfer over fiber is shaping up, but White Rabbit is
starting to grow up and more reports for long distances is showing up.
ETFT is one of the placces to check for reports.



And the White Rabbit workshops, with the presentations online:
http://www.ohwr.org/projects/white-rabbit/wiki/Mar2016Meeting

I happen to be working on time transfer via White Rabbit. The White Rabbit
standard proscribes the use of 1000Base-Bx10 (10km reach bi-directional)
SFPs, but it turns out to work just fine with longer reach SFPs. However,
there are several effects that limit the accuracy that you can get on longer
links:

* Dispersion of the fiber (as the lasers change temperature, their
wavelength changes, and they experience a slightly different index of
refraction, hence propagation speed.

* Change in index of refraction in the fiber itself. The propagation speed
of both the uplink and downlink wavelength change, in absolute sense but
also their ratio changes. This is something the WR protocol can't
detect/correct for.

There are several people working on these issues, trying to improve both the
calibration and stability even further.

Regards, Paul Boven.


___
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.



___
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.

Re: [time-nuts] Optical transfer of time and frequency

[Magnus Danielson]

Hi,

On 04/29/2016 11:45 PM, Michael Wouters wrote:

On Sat, Apr 30, 2016 at 6:14 AM, Magnus Danielson
 wrote:

Well, giving the conditions mentioned, doing ranging codes such as those
used by GPS is very easy and cheap. Doing this in bidirectional isn't too
hard. Doing a suitably high chip-rate should cost very little.


I've done two-way time-transfer over optical fibre using exactly this
technique. The TDEV is about 1 ps for tau>1s. Not so cheap, about 25K
euro per node (20K signal processing - NI FPGA, 2K laser and power
supplies, 1K detector, 1K RF electronics) in my setup, but that cost
could be greatly reduced since a $100 OEM FPGA could do the signal
processing (I've already done work on this but currently looking for
motivation to finish it off) and a simple, intensity-modulated laser
would probably be fine. A 2K euro budget would be a challenge though.


FPGA-wise, you need a very little FPGA resources.
If you consider the RedPitaya (200 USD) for instance, it is way beyond 
what is needed.



The two-way time-transfer is relatively easy, but you will need to do some
calibration to get the precision needed.



At first glance, I would think that you should be able to define the
optical RX/TX path to within 10 cm without any trouble and that gives
you 300 ps accuracy. Even on fibre links, I don't think anyone would
claim an accuracy of better than a few hundred ps.


With a bit of calibration you can remove each nodes systematic asymmetry.

For optical fibers many does not even bother to do a pseudorandom 
rangning. A repeating pattern suffice, such as that of SDH frames.


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.

Re: [time-nuts] Optical transfer of time and frequency

[Michael Wouters]

On Sat, Apr 30, 2016 at 6:14 AM, Magnus Danielson
 wrote:
> Well, giving the conditions mentioned, doing ranging codes such as those
> used by GPS is very easy and cheap. Doing this in bidirectional isn't too
> hard. Doing a suitably high chip-rate should cost very little.

I've done two-way time-transfer over optical fibre using exactly this
technique. The TDEV is about 1 ps for tau>1s. Not so cheap, about 25K
euro per node (20K signal processing - NI FPGA, 2K laser and power
supplies, 1K detector, 1K RF electronics) in my setup, but that cost
could be greatly reduced since a $100 OEM FPGA could do the signal
processing (I've already done work on this but currently looking for
motivation to finish it off) and a simple, intensity-modulated laser
would probably be fine. A 2K euro budget would be a challenge though.

> The two-way time-transfer is relatively easy, but you will need to do some
> calibration to get the precision needed.
>

At first glance, I would think that you should be able to define the
optical RX/TX path to within 10 cm without any trouble and that gives
you 300 ps accuracy. Even on fibre links, I don't think anyone would
claim an accuracy of better than a few hundred ps.

Cheers
Michael
___
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.

Re: [time-nuts] Optical transfer of time and frequency

[Bruce Griffiths]

White Rabbit would be good in that a suitable TDC design with 1ns resolution 
already exists for White Rabbit. This TDC is used in the Tunka valley (near 
lake Baikal) Siberian Cherenkov telescope array. Note this TDC uses the SERDES 
receiver in the FPGA to implement a serial to parallel converter with a 1GHz 
clock synthesised from the 125MHz White Rabbit clock.
So far I haven't found an existing free space optical implementation of White 
Rabbit.
Bruce
 

On Saturday, 30 April 2016 11:00 AM, Michael Wouters 
 wrote:
 

 So why not do White Rabbit free space ?

Cheers
Michael

On Sat, Apr 30, 2016 at 4:04 AM, Paul Boven  wrote:
> Hi everyone,
>
> On 04/29/2016 03:28 PM, Magnus Danielson wrote:
>>
>> Phase/time transfer over fiber is shaping up, but White Rabbit is
>> starting to grow up and more reports for long distances is showing up.
>> ETFT is one of the placces to check for reports.
>
>
> And the White Rabbit workshops, with the presentations online:
> http://www.ohwr.org/projects/white-rabbit/wiki/Mar2016Meeting
>
> I happen to be working on time transfer via White Rabbit. The White Rabbit
> standard proscribes the use of 1000Base-Bx10 (10km reach bi-directional)
> SFPs, but it turns out to work just fine with longer reach SFPs. However,
> there are several effects that limit the accuracy that you can get on longer
> links:
>
> * Dispersion of the fiber (as the lasers change temperature, their
> wavelength changes, and they experience a slightly different index of
> refraction, hence propagation speed.
>
> * Change in index of refraction in the fiber itself. The propagation speed
> of both the uplink and downlink wavelength change, in absolute sense but
> also their ratio changes. This is something the WR protocol can't
> detect/correct for.
>
> There are several people working on these issues, trying to improve both the
> calibration and stability even further.
>
> Regards, Paul Boven.
>
>
> ___
> 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.


   
___
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.

Re: [time-nuts] Optical transfer of time and frequency

[Michael Wouters]

So why not do White Rabbit free space ?

Cheers
Michael

On Sat, Apr 30, 2016 at 4:04 AM, Paul Boven  wrote:
> Hi everyone,
>
> On 04/29/2016 03:28 PM, Magnus Danielson wrote:
>>
>> Phase/time transfer over fiber is shaping up, but White Rabbit is
>> starting to grow up and more reports for long distances is showing up.
>> ETFT is one of the placces to check for reports.
>
>
> And the White Rabbit workshops, with the presentations online:
> http://www.ohwr.org/projects/white-rabbit/wiki/Mar2016Meeting
>
> I happen to be working on time transfer via White Rabbit. The White Rabbit
> standard proscribes the use of 1000Base-Bx10 (10km reach bi-directional)
> SFPs, but it turns out to work just fine with longer reach SFPs. However,
> there are several effects that limit the accuracy that you can get on longer
> links:
>
> * Dispersion of the fiber (as the lasers change temperature, their
> wavelength changes, and they experience a slightly different index of
> refraction, hence propagation speed.
>
> * Change in index of refraction in the fiber itself. The propagation speed
> of both the uplink and downlink wavelength change, in absolute sense but
> also their ratio changes. This is something the WR protocol can't
> detect/correct for.
>
> There are several people working on these issues, trying to improve both the
> calibration and stability even further.
>
> Regards, Paul Boven.
>
>
> ___
> 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.

Re: [time-nuts] Optical transfer of time and frequency

[Bruce Griffiths]

On Friday, April 29, 2016 10:14:11 PM Magnus Danielson wrote:
> Well, giving the conditions mentioned, doing ranging codes such as those
> used by GPS is very easy and cheap. Doing this in bidirectional isn't
> too hard. Doing a suitably high chip-rate should cost very little.
> 
> The two-way time-transfer is relatively easy, but you will need to do
> some calibration to get the precision needed.
> 
> Now, what is the needed precision?
> 
> Why can't you pull fiber?
> 
> Still wonder how you use the time, to understand the timing requirements.
Just need to be able to slot the photon arrival times into the correct slot on 
a common timebase.
Local regulations and the portable nature of the setup preclude running fibre, 
its also somewhat expensive to do so. Imaging requires that the Fourier plane 
be densely sampled so a number of baselines are necessary.

Bruce

> Cheers,
> Magnus
> 
> On 04/29/2016 08:50 PM, Ilia Platone wrote:
> > There is line of sight.
> > 
> > The budget is around 2k€ by now, but can be increased.
> > 
> > This project is for an amateur astro club, and the resources they would
> > give to me are limited, except the place where to do this and some optics.
> > 
> > The setup must be mobile, I mean that I should be able to place the
> > telescopes in other places "easily".
> > 
> > There is some material however. Material includes FPGA boards, VOCXO +
> > PLL boards, IR lasers and APD sensor boards, ARM boards, and consumer PCs.
> > 
> > There is also the possibility to use some optics like small reflector
> > telescopes, as pointed before, they could be used as beam expanders for
> > IR lasers.
> > 
> > Ilia.
> > 
> > Il 29/04/2016 09:36, Michael Wouters ha scritto:
> >> On Fri, Apr 29, 2016 at 1:18 PM, Bruce Griffiths
> >> 
> >>  wrote:
> >>> Quoting Michael Wouters: "According to this,
> >>> 
> >>> http://www.nist.gov/manuscript-publication-search.cfm?pub_id=912449
> >>> 
> >>> there are many practical challenges  with a one way free-space
> >>> optical link."
> >>> That paper indicates that  one way transfer with noise of a few
> >>> picosec should be feasible using an IR laser.
> >> 
> >> Oh, yes I see in Fig 2b that the short term, one-way noise is ca. +/-
> >> 5 ps. And probably with temperature measurements, the long term
> >> variation could be compensated.
> >> 
> >> But we still don't know if there is line of sight.
> >> 
> >> Cheers
> >> Michael
> >> ___
> >> 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.

___
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.

Re: [time-nuts] Optical transfer of time and frequency

[Ilia Platone]

Fiber is not what I need because the system will not be in fixed 
locations, and distances will be far more than 2km.


The requirements are to record photon arrival timestamps with a sampling 
clock of 400MHz, 2.5ns resolution. The two clocks are independent, and 
the timestamps will be the effective clock number at the photon arrival. 
An averaging algorithm will be used to normalize the timestamps.


Since the software I'll use can adjust some "small" time drift. Some 
clock cycle every houe is acceptable, so requirements, you see , are far 
to be impossible.


1 clock cycle = 2.5ns

max clock cycles @ 1 hour = can vary, 1024 would be a good value. 
Something achievable with commercial products and easily averagable by 
software.


So:

1280ns each 1H dT (less is well accepted).

Ilia.


Il 29/04/2016 22:14, Magnus Danielson ha scritto:
Well, giving the conditions mentioned, doing ranging codes such as 
those used by GPS is very easy and cheap. Doing this in bidirectional 
isn't too hard. Doing a suitably high chip-rate should cost very little.


The two-way time-transfer is relatively easy, but you will need to do 
some calibration to get the precision needed.


Now, what is the needed precision?

Why can't you pull fiber?

Still wonder how you use the time, to understand the timing requirements.

Cheers,
Magnus

On 04/29/2016 08:50 PM, Ilia Platone wrote:

There is line of sight.

The budget is around 2k€ by now, but can be increased.

This project is for an amateur astro club, and the resources they would
give to me are limited, except the place where to do this and some 
optics.


The setup must be mobile, I mean that I should be able to place the
telescopes in other places "easily".

There is some material however. Material includes FPGA boards, VOCXO +
PLL boards, IR lasers and APD sensor boards, ARM boards, and consumer 
PCs.


There is also the possibility to use some optics like small reflector
telescopes, as pointed before, they could be used as beam expanders for
IR lasers.

Ilia.


Il 29/04/2016 09:36, Michael Wouters ha scritto:

On Fri, Apr 29, 2016 at 1:18 PM, Bruce Griffiths
 wrote:

Quoting Michael Wouters: "According to this,

http://www.nist.gov/manuscript-publication-search.cfm?pub_id=912449

there are many practical challenges  with a one way free-space
optical link."
That paper indicates that  one way transfer with noise of a few
picosec should be feasible using an IR laser.

Oh, yes I see in Fig 2b that the short term, one-way noise is ca. +/-
5 ps. And probably with temperature measurements, the long term
variation could be compensated.

But we still don't know if there is line of sight.

Cheers
Michael
___
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.



--
Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999

___
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.

Re: [time-nuts] Optical transfer of time and frequency

[Magnus Danielson]

Well, giving the conditions mentioned, doing ranging codes such as those 
used by GPS is very easy and cheap. Doing this in bidirectional isn't 
too hard. Doing a suitably high chip-rate should cost very little.


The two-way time-transfer is relatively easy, but you will need to do 
some calibration to get the precision needed.


Now, what is the needed precision?

Why can't you pull fiber?

Still wonder how you use the time, to understand the timing requirements.

Cheers,
Magnus

On 04/29/2016 08:50 PM, Ilia Platone wrote:

There is line of sight.

The budget is around 2k€ by now, but can be increased.

This project is for an amateur astro club, and the resources they would
give to me are limited, except the place where to do this and some optics.

The setup must be mobile, I mean that I should be able to place the
telescopes in other places "easily".

There is some material however. Material includes FPGA boards, VOCXO +
PLL boards, IR lasers and APD sensor boards, ARM boards, and consumer PCs.

There is also the possibility to use some optics like small reflector
telescopes, as pointed before, they could be used as beam expanders for
IR lasers.

Ilia.


Il 29/04/2016 09:36, Michael Wouters ha scritto:

On Fri, Apr 29, 2016 at 1:18 PM, Bruce Griffiths
 wrote:

Quoting Michael Wouters: "According to this,

http://www.nist.gov/manuscript-publication-search.cfm?pub_id=912449

there are many practical challenges  with a one way free-space
optical link."
That paper indicates that  one way transfer with noise of a few
picosec should be feasible using an IR laser.

Oh, yes I see in Fig 2b that the short term, one-way noise is ca. +/-
5 ps. And probably with temperature measurements, the long term
variation could be compensated.

But we still don't know if there is line of sight.

Cheers
Michael
___
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.

Re: [time-nuts] Optical transfer of time and frequency

[Ilia Platone]

There is line of sight.

The budget is around 2k€ by now, but can be increased.

This project is for an amateur astro club, and the resources they would 
give to me are limited, except the place where to do this and some optics.


The setup must be mobile, I mean that I should be able to place the 
telescopes in other places "easily".


There is some material however. Material includes FPGA boards, VOCXO + 
PLL boards, IR lasers and APD sensor boards, ARM boards, and consumer PCs.


There is also the possibility to use some optics like small reflector 
telescopes, as pointed before, they could be used as beam expanders for 
IR lasers.


Ilia.


Il 29/04/2016 09:36, Michael Wouters ha scritto:

On Fri, Apr 29, 2016 at 1:18 PM, Bruce Griffiths
 wrote:

Quoting Michael Wouters: "According to this,

http://www.nist.gov/manuscript-publication-search.cfm?pub_id=912449

there are many practical challenges  with a one way free-space optical link."
That paper indicates that  one way transfer with noise of a few picosec should 
be feasible using an IR laser.

Oh, yes I see in Fig 2b that the short term, one-way noise is ca. +/-
5 ps. And probably with temperature measurements, the long term
variation could be compensated.

But we still don't know if there is line of sight.

Cheers
Michael
___
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.



--
Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999

___
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.

Re: [time-nuts] Optical transfer of time and frequency

[Paul Boven]

Hi everyone,

On 04/29/2016 03:28 PM, Magnus Danielson wrote:

Phase/time transfer over fiber is shaping up, but White Rabbit is
starting to grow up and more reports for long distances is showing up.
ETFT is one of the placces to check for reports.


And the White Rabbit workshops, with the presentations online:
http://www.ohwr.org/projects/white-rabbit/wiki/Mar2016Meeting

I happen to be working on time transfer via White Rabbit. The White 
Rabbit standard proscribes the use of 1000Base-Bx10 (10km reach 
bi-directional) SFPs, but it turns out to work just fine with longer 
reach SFPs. However, there are several effects that limit the accuracy 
that you can get on longer links:


* Dispersion of the fiber (as the lasers change temperature, their 
wavelength changes, and they experience a slightly different index of 
refraction, hence propagation speed.


* Change in index of refraction in the fiber itself. The propagation 
speed of both the uplink and downlink wavelength change, in absolute 
sense but also their ratio changes. This is something the WR protocol 
can't detect/correct for.


There are several people working on these issues, trying to improve both 
the calibration and stability even further.


Regards, Paul Boven.

___
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.

Re: [time-nuts] Optical transfer of time and frequency

[Magnus Danielson]

There is a lot of research going into frequency transfer and phase 
transfer links. The best long-distance link is one from PTB that goes to 
10-19 in stability. Marvelous stuff.


Phase/time transfer over fiber is shaping up, but White Rabbit is 
starting to grow up and more reports for long distances is showing up. 
ETFT is one of the placces to check for reports.


Microwave links such as those used in Two-way Satellite Time and 
Frequency Transfer works really well. SATRE modems of the shelf from 
TimeTech.


Cheers,
Magnus

On 04/29/2016 06:34 AM, Bob Stewart wrote:

I apologize for not following the original thread closely, but has anyone 
mentioned The White Rabbit Project?  Here's a wiki link.  Links from there to 
CERN, etc.  It might be beyond budget, etc.

en.wikipedia.org/wiki/The_White_Rabbit_Project

Bob

On Thu, 4/28/16, Bruce Griffiths <bruce.griffi...@xtra.co.nz> wrote:

  Subject: [time-nuts] Optical transfer of time and frequency
  To: "Discussion of Precise Time and Frequency Measurement" 
<time-nuts@febo.com>
  Date: Thursday, April 28, 2016, 10:18 PM

  Quoting Michael Wouters: "According
  to this,

  http://www.nist.gov/manuscript-publication-search.cfm?pub_id=912449

  there are many practical challenges  with a one way
  free-space optical link."
  That paper indicates that  one way transfer with noise of a
  few picosec should be feasible using an IR laser. Especially
  if only required at night for synchronisation of the
  timebases of the various telescope/detectors in a stellar
  intensity interferometer.
  Atmospheric scintillation should be lower as well as
  background noise from the sky, sun etc. The other factors
  like rain, hail, snow, fog etc aren't an issue  as these
  preclude observation of the stars of interest.
  Bruce


















  ___
  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.


___
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.

Re: [time-nuts] Optical transfer of time and frequency

[Bob Stewart]

I apologize for not following the original thread closely, but has anyone 
mentioned The White Rabbit Project?  Here's a wiki link.  Links from there to 
CERN, etc.  It might be beyond budget, etc.

en.wikipedia.org/wiki/The_White_Rabbit_Project

Bob

On Thu, 4/28/16, Bruce Griffiths <bruce.griffi...@xtra.co.nz> wrote:

 Subject: [time-nuts] Optical transfer of time and frequency
 To: "Discussion of Precise Time and Frequency Measurement" <time-nuts@febo.com>
 Date: Thursday, April 28, 2016, 10:18 PM
 
 Quoting Michael Wouters: "According
 to this,
 
 http://www.nist.gov/manuscript-publication-search.cfm?pub_id=912449
 
 there are many practical challenges  with a one way
 free-space optical link."
 That paper indicates that  one way transfer with noise of a
 few picosec should be feasible using an IR laser. Especially
 if only required at night for synchronisation of the
 timebases of the various telescope/detectors in a stellar
 intensity interferometer.
 Atmospheric scintillation should be lower as well as
 background noise from the sky, sun etc. The other factors
 like rain, hail, snow, fog etc aren't an issue  as these
 preclude observation of the stars of interest.
 Bruce
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ___
 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.

Re: [time-nuts] Optical transfer of time and frequency

[Azelio Boriani]

Yes, but I see that the allan deviation figures they cite aren't
achievable with common time-nuts gear now. Considering a VLBI project:
first premium stability then superb time transfer.

On Fri, Apr 29, 2016 at 5:18 AM, Bruce Griffiths
 wrote:
> Quoting Michael Wouters: "According to this,
>
> http://www.nist.gov/manuscript-publication-search.cfm?pub_id=912449
>
> there are many practical challenges  with a one way free-space optical link."
> That paper indicates that  one way transfer with noise of a few picosec 
> should be feasible using an IR laser. Especially if only required at night 
> for synchronisation of the timebases of the various telescope/detectors in a 
> stellar intensity interferometer.
> Atmospheric scintillation should be lower as well as background noise from 
> the sky, sun etc. The other factors like rain, hail, snow, fog etc aren't an 
> issue  as these preclude observation of the stars of interest.
> Bruce
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> ___
> 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.

Re: [time-nuts] Optical transfer of time and frequency

[Michael Wouters]

On Fri, Apr 29, 2016 at 1:18 PM, Bruce Griffiths
 wrote:
> Quoting Michael Wouters: "According to this,
>
> http://www.nist.gov/manuscript-publication-search.cfm?pub_id=912449
>
> there are many practical challenges  with a one way free-space optical link."
> That paper indicates that  one way transfer with noise of a few picosec 
> should be feasible using an IR laser.

Oh, yes I see in Fig 2b that the short term, one-way noise is ca. +/-
5 ps. And probably with temperature measurements, the long term
variation could be compensated.

But we still don't know if there is line of sight.

Cheers
Michael
___
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.

Re: [time-nuts] Optical transfer of time and frequency

[Bruce Griffiths]

There's more relevant data on optical free space time and frequency transfer 
here:http://www.nist.gov/manuscript-publication-search.cfm?pub_id=915083


Bruce



On Friday, 29 April 2016 4:01 PM, Bruce Griffiths 
 wrote:
 

 Quoting Michael Wouters: "According to this,

http://www.nist.gov/manuscript-publication-search.cfm?pub_id=912449

there are many practical challenges  with a one way free-space optical link."
That paper indicates that  one way transfer with noise of a few picosec should 
be feasible using an IR laser. Especially if only required at night for 
synchronisation of the timebases of the various telescope/detectors in a 
stellar intensity interferometer.
Atmospheric scintillation should be lower as well as background noise from the 
sky, sun etc. The other factors like rain, hail, snow, fog etc aren't an issue  
as these preclude observation of the stars of interest.
Bruce


















___
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.

[time-nuts] Optical transfer of time and frequency

[Bruce Griffiths]

Quoting Michael Wouters: "According to this,

http://www.nist.gov/manuscript-publication-search.cfm?pub_id=912449

there are many practical challenges  with a one way free-space optical link."
That paper indicates that  one way transfer with noise of a few picosec should 
be feasible using an IR laser. Especially if only required at night for 
synchronisation of the timebases of the various telescope/detectors in a 
stellar intensity interferometer.
Atmospheric scintillation should be lower as well as background noise from the 
sky, sun etc. The other factors like rain, hail, snow, fog etc aren't an issue  
as these preclude observation of the stars of interest.
Bruce


















___
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.