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 +0000 >> 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 in this way. >> > >> >> This is a good point, and something we'll make sure to keep in mind... >> >> Thanks again, >> Jack >> >> >> >> > >> > Regards >> > >> > Johan Burger >> > >> > >> > >> > >> > >> > For MeerKAT high precision timing a special PPS solution is used. There >> > are seperate PPS transmitters and >> > On Tue, May 5, 2015 at 7:56 PM, Michael Inggs <miki...@gmail.com> >> wrote: >> > >> >> Hi >> >> >> >> We have a complete White Rabbit setup, including 5km fibre test reels. >> It >> >> is driven by a Meinberg Plenum 1 clock. We are quite happy to chat with >> >> anyone on this topic of phase coherence. As you all know, the hardware >> and >> >> firmware is all Open Source, so as Jason mentions, easy to >> incorporate. I >> >> think I saw that the new CASPER card has provision for WR? Members of >> the >> >> team have specialised GPSDO systems developed in the lab that seem to >> give >> >> below 10 ns of jitter. >> >> >> >> Someone has tested it over 900km and beyond in Norway and sub ps jitter >> >> is achieved. >> >> >> >> One drawback is it needs a 1Ge fibre link, which I guess means, these >> >> days, its own fibre. We spoke to CERN about developing 10Ge and above, >> but >> >> it looks complex due to the many channels embedded in these streams. >> There >> >> has been some good work on sending it over microwave, but I guess that >> is a >> >> no-no for astronomy reserves. >> >> >> >> Regards >> >> >> >> >> >> >> >> On 5 May 2015 at 19:27, Jason Manley <jman...@ska.ac.za> wrote: >> >> >> >>> White rabbit is the version of IEEE1588 that locks bit clocks. Normal >> >>> IEEE1588 doesn't do this. For this reason, (last I looked), there was >> no >> >>> 10G implementation. 1G speeds is the highest White Rabbit >> implementation. >> >>> The HW support for "normal" IEEE1588 is used to timestamp the packets >> >>> without software in the loop (where the CPU will introduce jitter). >> >>> >> >>> But you don't necessarily need any special HW for IEEE1588... it can >> all >> >>> be done in a normal FPGA using the standard Xilinx 10G IP core. There >> are >> >>> FPGA cores available for the IEEE1588 part, so you don't have to >> implement >> >>> it yourself. We considered this for MeerKAT at one stage, but in the >> end we >> >>> couldn't achieve the required performance. It might be quite workable >> for >> >>> HERA, though. Anyway, just a thought. It'd save you buying special HW >> and >> >>> running additional fibres, if it meets your performance targets. >> >>> >> >>> Jason Manley >> >>> CBF Manager >> >>> SKA-SA >> >>> >> >>> Cell: +27 82 662 7726 >> >>> Work: +27 21 506 7300 >> >>> >> >>> On 05 May 2015, at 18:49, Dan Werthimer <d...@ssl.berkeley.edu> >> wrote: >> >>> >> >>> > >> >>> > >> >>> > hi dave, >> >>> > >> >>> > i also think distributing clock and 1 PPS is simpler than IEEE1588. >> >>> > >> >>> > some of the IEEE1588 and white rabbit experts are here at berkeley. >> >>> > see for example: >> >>> > http://chess.eecs.berkeley.edu/pubs/881/dreams.pdf >> >>> > >> >>> > my limited understanding is that 1588 phase locks the bit clocks of >> >>> > routers and switches together. 1588 routers and switches have SMA >> >>> > connectors on them so you can use external maser/rubidium/GPS >> >>> references. >> >>> > >> >>> > you can achieve spectacular accuracy and stabilitity with white >> rabbit >> >>> > if you employ really good oscillators at each node, >> >>> > i think white rabbit can acheive 70 picosecond RMS time transfer. >> >>> > >> >>> > best, >> >>> > >> >>> > dan >> >>> > >> >>> > >> >>> > >> >>> > >> >>> > >> >>> > On Tue, May 5, 2015 at 8:52 AM, David MacMahon < >> >>> dav...@astro.berkeley.edu> wrote: >> >>> > Hi, Jason, >> >>> > >> >>> > I have a great deal of curiosity about IEEE-1588, but I've always >> >>> wondered about the precision/stability that's attainable. Compared >> with >> >>> multiple sample clocks, correlating signals sampled with one common >> clock >> >>> seems far more forgiving vis a vis clock frequency/phase stability. >> If you >> >>> or John could point me to any information about this, please do! >> >>> > >> >>> > Thanks, >> >>> > Dave >> >>> > >> >>> > On May 4, 2015, at 11:44 PM, Jason Manley wrote: >> >>> > >> >>> > > On the far end of the concept spectrum, have you considered >> >>> distributing time over your existing ethernet network with IEEE-1588, >> and >> >>> using this to discipline local ovenised 10MHz oscs at each antenna? >> >>> > > >> >>> > > I'm cc'ing Johan Burger, who heads up our Timing and Frequency >> >>> Reference subsystem, who might be able to offer some additional >> insight. I >> >>> know they've tried a few different lasers and detectors, with varying >> >>> levels of success. >> >>> > > >> >>> > > Jason Manley >> >>> > > CBF Manager >> >>> > > SKA-SA >> >>> > > >> >>> > > Cell: +27 82 662 7726 >> >>> > > Work: +27 21 506 7300 >> >>> > > >> >>> > > On 05 May 2015, at 5:18, Bob Stricklin <bstr...@n5brg.com> wrote: >> >>> > > >> >>> > >> Hi Jack and John, >> >>> > >> >> >>> > >> I wanted to add an input here?.. >> >>> > >> >> >>> > >> I am working on a 10 MHz GPS slaved reference for my personal >> use. >> >>> I am working with a Analog Devices AD9548 Evaluation board (~$250) , >> GPS >> >>> with 1 PPS, and a ovenized 10 MHz osc. I also plan to distribute this >> clock >> >>> and have considered the Avago fiber product line. One of the older >> >>> generation Avago fiber parts should work fine for <$25 per channel. >> With >> >>> careful control of lengths and delays it should be possible to >> maintain >> >>> good phasing between channels. The analog devices chip is <$50 so a >> custom >> >>> solution should be <$500/reference but with considerable development >> time. >> >>> > >> >> >>> > >> Bob Stricklin >> >>> > >> >> >>> > >> >> >>> > >>> On May 4, 2015, at 10:02 PM, Jack Hickish < >> jackhick...@gmail.com> >> >>> wrote: >> >>> > >>> >> >>> > >>> Hi John, >> >>> > >>> >> >>> > >>> Thanks for the info. I'll add Litelink to my list of suppliers >> to >> >>> investigate. >> >>> > >>> We have no particular urge to multiplex the signals on to the >> >>> fiber unless there's a particularly neat/cheap solution to do that. >> There's >> >>> no great appetite to go custom. We've got about ~30 nodes, and my >> first >> >>> stab at getting an off-the-shelf solution turned up at a few k$ / >> node, not >> >>> including any cleanup electronics. >> >>> > >>> >> >>> > >>> Thanks again, >> >>> > >>> >> >>> > >>> Jack >> >>> > >>> >> >>> > >>> On Mon, 4 May 2015 at 19:25 John Ford <jf...@nrao.edu> wrote: >> >>> > >>>> Hi CASPERites, >> >>> > >>>> >> >>> > >>>> For HERA, we're looking at distributing timing signals (PPS & >> >>> 10Mhz ref or >> >>> > >>>> 500 MHz clock) over O(100m) fibers to various digitization >> nodes. >> >>> > >>>> I figure some folks in CASPERland have experience with this >> kind >> >>> of >> >>> > >>>> system? >> >>> > >>>> Did you use custom RF-over-fiber kit, or off-the-shelf >> PPS/10MHz >> >>> > >>>> solutions? >> >>> > >>>> Any words of wisdom/caution to share? >> >>> > >>>> >> >>> > >>>> Any responses much appreciated! >> >>> > >>> >> >>> > >>> We have several different schemes for the different signals. >> Are >> >>> you >> >>> > >>> planning for one fiber per signal per node? or one fiber with >> the >> >>> signals >> >>> > >>> multiplexed on them? >> >>> > >>> >> >>> > >>> If the signals are one per signal, you can use some >> off-the-shelf >> >>> > >>> solutions, but they are kind of pricey, and if you have a lot of >> >>> nodes to >> >>> > >>> supply, it might be worth working on something custom. We have >> >>> used Math >> >>> > >>> Associates stuff for this kind of work. Math Associates is now >> >>> litelink, >> >>> > >>> and they tout the affordability of their stuff, so maybe it's >> >>> > >>> reasonable... >> >>> > >>> >> >>> > >>> >> >>> > >>> On the 10 MHz, we send the 10 MHz reference over fiber, and at >> the >> >>> far end >> >>> > >>> use a crystal oscillator locked to the reference to clean up the >> >>> noise >> >>> > >>> from the fiber electronics. This is essential for >> interferometry, >> >>> but >> >>> > >>> maybe not for single-dish use. >> >>> > >>> >> >>> > >>> John >> >>> > >>> >> >>> > >>>> >> >>> > >>>> Jack >> >>> > >>>> >> >>> > >>> >> >>> > >>> >> >>> > >> >> >>> > > >> >>> > > >> >>> > >> >>> > >> >>> > >> >>> >> >>> >> >>> >> >> >> >> >> >> -- >> >> Michael Inggs >> >> Department of Electrical Engineering, University of Cape Town, Private >> >> Bag, Rondebosch 7701, South Africa. Tel: +27 21 650 2799 Fax: +27 21 >> 650 >> >> 3465 Skype: mikings >> >> "Ex Africa semper aliquid novi" >> >> >> >> >> > >> -------------- next part -------------- >> An HTML attachment scrubbed and removed. >> HTML attachments are only available in MIME digests. >> >> End of casper Digest, Vol 90, Issue 10 >> ************************************** >> > > > > -- > Dr Andrew van der Byl > > Mobile: +27 83 312 7392 > Email: a <andrew.vander...@gmail.com>vd...@gmail.com >
