[time-nuts] Optical transfer of time and frequency

Ilia Platone info at iliaplatone.com
Sat Apr 30 18:35:15 EDT 2016


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 <magnus at rubidium.dyndns.org> wrote:
>   
>
>   Hi,
>
> On 04/29/2016 11:45 PM, Michael Wouters wrote:
>> On Sat, Apr 30, 2016 at 6:14 AM, Magnus Danielson
>> <magnus at rubidium.dyndns.org> 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
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>     
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Ilia Platone
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