Re: [casper] casper Digest, Vol 90, Issue 10
Hi all, For those interested in White Rabbit, Xilinx have an article in their Xcell journal (91). The link is here http://issuu.com/xcelljournal/docs/xcell_journal_issue_91/18?e. regards, Andrew On Thu, May 7, 2015 at 1:45 AM, casper-requ...@lists.berkeley.edu 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 jackhick...@gmail.com Subject: Re: [casper] Timing distribution over fiber To: Johan Burger jbur...@ska.ac.za, Michael Inggs miki...@gmail.com,Bob Stricklin bstr...@n5brg.com, Sias Malan s...@ska.ac.za, Renier Siebrits ren...@ska.ac.za, Francois Kapp franc...@ska.ac.za, Etienne Bauermeister etie...@ska.ac.za Cc: Simon Lewis simonacle...@hotmail.com, Casper Lists casper@lists.berkeley.edu,Thomas Abbott tabb...@ska.ac.za, Stephan Sandenberg ssandenbe...@gmail.com Message-ID: CAG1GKS=5fWeJ+quOj= gj_rd7qgtngc2z_07abtx7nwjhojw...@mail.gmail.com Content-Type: text/plain; charset=utf-8 On Wed, 6 May 2015 at 07:35 Johan Burger jbur...@ska.ac.za 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
Re: [casper] casper Digest, Vol 90, Issue 10
Thanks for the link, Andrew! On Thu, 7 May 2015 at 05:09 Andrew Vdb avd...@gmail.com wrote: Hi all, For those interested in White Rabbit, Xilinx have an article in their Xcell journal (91). The link is here http://issuu.com/xcelljournal/docs/xcell_journal_issue_91/18?e. regards, Andrew On Thu, May 7, 2015 at 1:45 AM, casper-requ...@lists.berkeley.edu 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 jackhick...@gmail.com Subject: Re: [casper] Timing distribution over fiber To: Johan Burger jbur...@ska.ac.za, Michael Inggs miki...@gmail.com,Bob Stricklin bstr...@n5brg.com, Sias Malan s...@ska.ac.za, Renier Siebrits ren...@ska.ac.za, Francois Kapp franc...@ska.ac.za, Etienne Bauermeister etie...@ska.ac.za Cc: Simon Lewis simonacle...@hotmail.com, Casper Lists casper@lists.berkeley.edu,Thomas Abbott tabb...@ska.ac.za , Stephan Sandenberg ssandenbe...@gmail.com Message-ID: CAG1GKS=5fWeJ+quOj= gj_rd7qgtngc2z_07abtx7nwjhojw...@mail.gmail.com Content-Type: text/plain; charset=utf-8 On Wed, 6 May 2015 at 07:35 Johan Burger jbur...@ska.ac.za 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
