Re: [casper] casper Digest, Vol 90, Issue 10

[Jack Hickish]

Thanks for the link, Andrew!

On Thu, 7 May 2015 at 05:09 Andrew Vdb  wrote:

> Hi all,
>
> For those interested in White Rabbit, Xilinx have an article in their
> Xcell journal (91). The link is here
> .
>
> regards,
> Andrew
>
> On Thu, May 7, 2015 at 1:45 AM,  wrote:
>
>> Send casper mailing list submissions to
>> casper@lists.berkeley.edu
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>> Today's Topics:
>>
>>1. Re: Timing distribution over fiber (Jack Hickish)
>>
>>
>> --
>>
>> Message: 1
>> Date: Wed, 06 May 2015 23:45:53 +
>> From: Jack Hickish 
>> Subject: Re: [casper] Timing distribution over fiber
>> To: Johan Burger , Michael Inggs
>> ,Bob Stricklin , Sias
>> Malan
>> ,   Renier Siebrits ,
>> Francois Kapp
>> ,   Etienne Bauermeister 
>> Cc: Simon Lewis , Casper Lists
>> ,Thomas Abbott > >,
>> Stephan Sandenberg 
>> Message-ID:
>> > gj_rd7qgtngc2z_07abtx7nwjhojw...@mail.gmail.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> On Wed, 6 May 2015 at 07:35 Johan Burger  wrote:
>>
>> >
>> > Hi there,
>> >
>> > Do you maybe have any idea of requirement specifications for the HERA's
>> RF
>> > phase stability and time (?) - this might determine what technology
>> could
>> > be appropriate.
>> >
>>
>> Hi Johan,
>>
>> Thanks for your response. We're sampling at 500 MHz, so we'd like to have
>> a
>> stability of "few" degrees, preferably over timescales of many hours but
>> perhaps more reasonably on a calibration cadence of O(10 minutes)
>>
>> PPS is not such a big deal, and synchronization to a couple of ADC clock
>> cycles is probably fine. We're investigating simple-ish ways to calibrate
>> these out with signal injection.
>>
>>
>>
>> >
>> > We at SKA Africa have after some iteration come up, with a precision RF
>> > distribution system for many antennas.  The type of laser and integrated
>> > modulator have been proven in the field on large arrays (not just
>> > MeerKAT).  The RF can be directly transmitted (in our case up to 2-3 GHz
>> > limited by our synthesizer - the precise frequency is 1.712GHz).
>> 500MHz RF
>> > over fibre can be done by this as well.  There is conditioning of the RF
>> > taking place on MeerKAT at the receiving end. As Jason said, not any or
>> all
>> > modules really do the job properly - we converged on a solution after
>> > testing, that implicitly included modules evaluated from KAT-7 days, and
>> > more recent modules from other manufacturers.
>> >
>> > "Low precision" timing ~100ns can indeed be done using PTP.  If PPS is
>> > required instead of an Ethernet package a special conversion board
>> (PCIe)
>> > is necessary.  This is really enough for fringe finding - used in
>> MeerKAT
>> > S-band for example. That digitiser is mounted in an RFI shielded
>> pedestal
>> > of the antenna though.  We supply the high precision PPS using our
>> custom
>> > system as described below.
>> >
>> > For our L-band digitisers mounted on the outside we had to come up with
>> > special low power, low cost, high accuracy solution - this is being
>> > implemented by Renier and Etienne and others here at SKA Africa (so a
>> joint
>> > effort by our time and frequency and digitiser team).  The reason is
>> that
>> > White Rabbit is not compatible with 10Gbe links used on this system.
>> > Furthermore Ethernet is actually quite noisy as per MeerKAT
>> measurements,
>> > and White Rabbit and PTP uses that (and with highish power consumption
>> and
>> > largish board size), and is not preferable in a high purity clock signal
>> > and PPS module.  We found that measurement based PPS system will meet
>> our
>> > requirements though, for stabilized links and provides us with accurate
>> > absolute time references at antennas, using analog methodologies.  This
>> for
>> > example being important in pulsar science.
>> >
>> > I am not sure what level of RFI shielding you would be able to mount
>> > around modules, but as said RFI from Ethernet has certainly been found
>> to
>> > be an RFI culprit, and cannot be therefore be used in MeerKAT close to
>> > sensitive modules - and needs to separately shielded.  This therefore
>> means
>> > that if PPS is generated from White Rabbit/PTP there is still some
>> > uncertain propagation paths left (important at least for MeerKAT) up to
>> the
>> > point of digitization where a timing edge is inserted.  We are using
>> > sepe

Re: [casper] casper Digest, Vol 90, Issue 10

[Andrew Vdb]

Hi all,

For those interested in White Rabbit, Xilinx have an article in their Xcell
journal (91). The link is here
.

regards,
Andrew

On Thu, May 7, 2015 at 1:45 AM,  wrote:

> Send casper mailing list submissions to
> casper@lists.berkeley.edu
>
> To subscribe or unsubscribe via the World Wide Web, visit
>
> https://calmail.berkeley.edu/manage/list/listinfo/casper@lists.berkeley.edu
>
> or, via email, send a message with subject or body 'help' to
> casper-requ...@lists.berkeley.edu
>
> You can reach the person managing the list at
> casper-ow...@lists.berkeley.edu
>
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of casper digest..."
>
>
> Today's Topics:
>
>1. Re: Timing distribution over fiber (Jack Hickish)
>
>
> --
>
> Message: 1
> Date: Wed, 06 May 2015 23:45:53 +
> From: Jack Hickish 
> Subject: Re: [casper] Timing distribution over fiber
> To: Johan Burger , Michael Inggs
> ,Bob Stricklin , Sias
> Malan
> ,   Renier Siebrits ,
> Francois Kapp
> ,   Etienne Bauermeister 
> Cc: Simon Lewis , Casper Lists
> ,Thomas Abbott ,
> Stephan Sandenberg 
> Message-ID:
>  gj_rd7qgtngc2z_07abtx7nwjhojw...@mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> On Wed, 6 May 2015 at 07:35 Johan Burger  wrote:
>
> >
> > Hi there,
> >
> > Do you maybe have any idea of requirement specifications for the HERA's
> RF
> > phase stability and time (?) - this might determine what technology could
> > be appropriate.
> >
>
> Hi Johan,
>
> Thanks for your response. We're sampling at 500 MHz, so we'd like to have a
> stability of "few" degrees, preferably over timescales of many hours but
> perhaps more reasonably on a calibration cadence of O(10 minutes)
>
> PPS is not such a big deal, and synchronization to a couple of ADC clock
> cycles is probably fine. We're investigating simple-ish ways to calibrate
> these out with signal injection.
>
>
>
> >
> > We at SKA Africa have after some iteration come up, with a precision RF
> > distribution system for many antennas.  The type of laser and integrated
> > modulator have been proven in the field on large arrays (not just
> > MeerKAT).  The RF can be directly transmitted (in our case up to 2-3 GHz
> > limited by our synthesizer - the precise frequency is 1.712GHz).  500MHz
> RF
> > over fibre can be done by this as well.  There is conditioning of the RF
> > taking place on MeerKAT at the receiving end. As Jason said, not any or
> all
> > modules really do the job properly - we converged on a solution after
> > testing, that implicitly included modules evaluated from KAT-7 days, and
> > more recent modules from other manufacturers.
> >
> > "Low precision" timing ~100ns can indeed be done using PTP.  If PPS is
> > required instead of an Ethernet package a special conversion board (PCIe)
> > is necessary.  This is really enough for fringe finding - used in MeerKAT
> > S-band for example. That digitiser is mounted in an RFI shielded pedestal
> > of the antenna though.  We supply the high precision PPS using our custom
> > system as described below.
> >
> > For our L-band digitisers mounted on the outside we had to come up with
> > special low power, low cost, high accuracy solution - this is being
> > implemented by Renier and Etienne and others here at SKA Africa (so a
> joint
> > effort by our time and frequency and digitiser team).  The reason is that
> > White Rabbit is not compatible with 10Gbe links used on this system.
> > Furthermore Ethernet is actually quite noisy as per MeerKAT measurements,
> > and White Rabbit and PTP uses that (and with highish power consumption
> and
> > largish board size), and is not preferable in a high purity clock signal
> > and PPS module.  We found that measurement based PPS system will meet our
> > requirements though, for stabilized links and provides us with accurate
> > absolute time references at antennas, using analog methodologies.  This
> for
> > example being important in pulsar science.
> >
> > I am not sure what level of RFI shielding you would be able to mount
> > around modules, but as said RFI from Ethernet has certainly been found to
> > be an RFI culprit, and cannot be therefore be used in MeerKAT close to
> > sensitive modules - and needs to separately shielded.  This therefore
> means
> > that if PPS is generated from White Rabbit/PTP there is still some
> > uncertain propagation paths left (important at least for MeerKAT) up to
> the
> > point of digitization where a timing edge is inserted.  We are using
> > seperate fibres for PPS and RF, to further limit self-RFI and as it was
> > found that requirements could only be met in this way.
> >
>
> This is a good point, and something we'll make sure to keep in mind...
>
> Thanks again,
> Jack
>
>
>
> >