PoS(EVN 2014)031 http://pos.sissa.it/ [email protected] , b , A. Szomoru a ∗ [email protected] Speaker. The European VLBI Network has evolvedpossible significantly during by recent the years. addition This of hasthe new been emergence antennas, of made high the bandwidth introduction optical fibre ofrecently, by networks, the the the Mark upgrade SFXC 5 to software digital recording correlator, backends and systemthe at most array and the and stations. outline Here some we of describe the the planned present future status technical of directions. ∗ Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. c

12th European VLBI Network Symposium and7-10 Users October Meeting, 2014 Cagliari, Italy M. Lindqvist Present status and technical directions of the EVN Department of Earth and Space Sciences,Onsala Chalmers Space University , of SE-439 Technology 92 Onsala,Joint Sweden Institute for VLBI in Europe Posbus 2, 7990 AA Dwingeloo, TheE-mail: Netherlands a b PoS(EVN 2014)031 M. Lindqvist . New telescopes includes 1 305 m), Figure − 2 1000 TB). For a station participating in most users experi- 60 TB. In addition, the EVN also offers ten 24 hour e-VLBI > − 800 TB (the current record is The EVN currently observes during 3 periods per year known as “EVN sessions”. Each of The maximum data rate is 1 Gbps (corresponding to an observing bandwidth of 128 MHz, dual The situation at the EVN stations is fairly diverse with respect to data-acquisition systems. Very Long Baseline (VLBI) is an important, and in many respects unique, Another important body of the EVN is the Technical and Operations Group (TOG). It consists The EVN operates about 21 individual telescopes, which include some of the world’s largest − these sessions is approximatelyquencies 21 (sometimes days up long to 5). and The700 typically total involves amount 3-4 of disk different media observing used in fre- an EVN session is currently polarization, 2-bit sampling), both for disk recordingadds and the e-VLBI. NRAO Since Very 2014 Long Global Baseline VLBI1 (which Array Gbps (VLBA) (disk and/or recording) other as well. NRAO antennas) can be done at However, all stations record the data using the Mark 5 system developed by the Haystack Ob- the Yebes 40 m telescope inskaya Spain and and Badary). the They Russian mademost 32 m their recent addition first KVAZAR stations to EVN the (Svetloe, observations EVN Zelenchuk- sei, in family includes 2008 Ulsan, the and Korean Tamna), 2010, VLBI the respectively. Networkcommissioning 21 The Shanghai m phase telescopes but Tianma (Yon- will 65 be m available on telescope. a “best The efforts” basis Sardinia from 64 2015 m on. telescope is in a ments this means a disksessions load of per 50 year, approximatelytechnique once enables per real-time month data transfer outside fromalso the the possible main stations to to EVN propose JIVE for sessions. viascheduling Out-of optical Session is fibre The as done networks. e-VLBI well by It as is 6 the Target-of cm. Opportunity EVN Other observing scheduler. observing time. wavebands include The The 90, most 21, common 13, 5, observing 4, wavebands 1 are and 0.7 18 cm. and observing method, with aSquare strong Kilometre synergy Array with (SKA). One e.g. of(EVN). the the 15 Low-Frequency major radio VLBI Array astronomical networks (LOFAR) institutes is andin (including the Europe, the the European Asia, VLBI Joint South Network Africa Institute and for thehave VLBI Americas any in form central the Europe funding. EVN. (JIVE)) The It was EVNpolicy created Consortium of in Board the 1980 of and EVN. Directors does Astronomers (CBD) not the determines who EVN Programme the wish Committee. overall to Proposals use are(the accepted the EVN from EVN, astronomers operates from as must all an submit over “open the observing sky” world observatory). proposals to of personnel from the EVNnical stations and (such operational as expertise the for VLBI operatingCBD friends, the on see EVN all below) as aspects and a of provides VLBIof technical the array. the and tech- The network operational TOG and issues also implements relevant advises technicalthe to the and current the status operational reliability of upgrades. and the In performance EVN this and paper outline we some will of the describe future developments. 2. Current status and most sensitive radio telescopes (ranging from 14 Present status and technical directions of the EVN 1. Introduction PoS(EVN 2014)031 ]), 16 M. Lindqvist 9 months to discuss − ]) while Robledo has just 8 . Each frequency block almost al- 2 3 The European VLBI Network (credit: P. Boven, JIVE). ]). All of these systems are capable of handling a recording rate of at least 4 ]), the Russian KVAZAR stations have their own digital BBC called the 11 ]). Several stations are in the process of replacing (or have already replaced) Figure 1: 14 ], [ 24 hours after the experiment. The TOG typically meets every 8 13 ]), the Chinese stations use the Chinese VLBI Data Acquisition System CDAS ([ < 3 Most of the data are correlated at JIVE but it is also possible to use the correlator at the Max- The station VLBI friend is responsible for the EVN session at his/her station. The different Planck Institut für Radioastronomie in Bonn, Germany or the NRAO correlator in Soccorro, USA. recent sessions (here the feedbackplans from for JIVE the to future. thenormally stations The a major is accuracy agenda of of point utmost the at importance) the EVN TOG-meetings. as amplitude well calibration as (and how to improve it) is ways starts with a Network Monitoring Experimentvarious (NME). tests The of purpose of the the network. NMEcorrecting is The problems to NME perform before also the includes actualblock a the user fringe VLBI experiments friend test, following also which checks theature is and NME. calibration. extremely if For useful necessary These each updates for data the frequency areaim gain later to curve stored and produce in the calibration the system information so temper- weeks called (i.e., after ANTAB-file. the the The ANTAB-file) end VLBI for ofsuch friend each data an must user EVN experiment session. within For 2 an e-VLBI session the VLBI friend should provide components of a typical EVN session are shown in Figure servatory ([ 2 Gbps (corresponding to an observing bandwidth of 256 MHz, dual polarization, 2-bit sampling). R1002 ([ their old analog data-acquisition systems (whichConverter are (DBBC, limited to [ 1 Gbps) with the Digital Base Band Arecibo uses the Haystack/NRAOstarted Roach commissioning Digital another Backend digital BBC, (RDBE, developedVLBI [ by Processor NASA, (DVP, [ called the Deep Space Network Present status and technical directions of the EVN PoS(EVN 2014)031 M. Lindqvist ]). In the rest of the paper we will 2 ], [ 1 4 The components of a typical EVN session. ]). In the near future, we expect to add the 32 m , the top priority for the EVN users is to have more telescopes and 5 1 . The average rank is an indication for the way the EVN users see the 1 Figure 2: Before investigating various technical possibilities it is interesting to start with the most pre- As can be seen in Table ]) or the Distributed FX (DiFX) software correlator ([ 7 more shorter spacing. Awith natural all way its forward out-stations and atuv-coverage towards currently 1 the Gbps under south (and (i.e., testing Hartebeesthoek, beyond). South is(AVN) Africa). It is to Here an would include the interesting also Africa e-Merlin VLBI project be Network aiming veryin to interesting many convert to old African satellite improve countries telecommunications the antennas ([ found cious assets of the network, thebased EVN on users. their They importance were to askedresults to his/her are rank science given a in during series Table an of items evaluation in of the JIVE order a few years ago. The only discuss the SFXC. 3. Future possibilities future of the EVN.CBD, When this discussing must be future taken possibilities into for account. the EVN, both3.1 in New the telescopes and TOG collaborations and the All of these correlators are software-based[ using either the EVN SFXC Correlator at JIVE (SFXC, Present status and technical directions of the EVN PoS(EVN 2014)031 ]. The 6 M. Lindqvist 5 EVN capabilities and their ranking by EVN users. Table 1: ]). 9 2.733.504.57 Improved uv-coverage (more telescopes, more short4.60 Increased spacings) bandwidth to improve sensitivity 4.73 Improved calibration in general (phase,6.06 amplitude, Improved bandpass, resolution polarization) (more long baselines) 6.34 Frequency agility for spectral index6.42 imaging Real-time e-VLBI capabilities for more6.71 telescopes Extended observing time to be6.89 able Real-time to e-VLBI carry capabilities out for big a surveys larger Improved fraction astrometry of observing time Larger field of view Another observing class to be offered by the EVN will allow an observation to be sched- EVN is not a full time array like the VLBA. This has led to a concept called “EVN light” In 2014 the EVN and the Long Baseline Array (LBA) in Australia announced the possibility Average rank Item uled automatically during an e-VLBI runa if VOEvent a (a specific standardized set of languagemated/manual triggering trigger used criteria response). to is met report The (e.g.10 astronomical expected through minutes. events) response or time The to other station executecoordinates form a experiment need of new only setup auto- program be will is included befirst in about time the the the same EVN trigger considers as request, generic the not triggers. in interrupted the program. original proposal. Source This is the EVN also opened up the144 hours/year), observing class for all Out-of-Session projects (OoS)EVN/Global+RadioAstron. during observing Proposals 2014. (up requesting to OoS Up observing a(and until time maximum technical then, must of if OoS provide appropriate) observing fullEVN scientific had justification sessions. been as limited to to why observations must be made outside regular where the smaller antennas operate assuch an a array concept include outside e.g. the long-term majorIf maser EVN there monitoring sessions. is and Science a fast automated areas sufficient interest response for how observations. from to the operate user such community an thesee array EVN no in should major terms investigate technical in of problems more proposals, here. detail scheduling, correlation and user3.2 support. New We observing modes to combine the arrays.telescopes The in first Australia, attempt to China,time truly Europe, combine e-VLBI Japan, EVN experiment as and was well LBAYear done telescopes of as during (and Astronomy North- a in in and demo fact 2009. South-America) at in the This a opening was ceremony real- later of followed the up International in a real science experiment [ at Irbene, operated by VentspilsFurther International in the Center future intoMiyun we telescope, the the envision EVN 40 the operations. m Kunming collaborationthe telescope SKA with and ([ the telescopes 500 m in FAST), Meerkat China in (such South Africa as and the 50 m Present status and technical directions of the EVN PoS(EVN 2014)031 M. Lindqvist ]), it will be possible to 12 6 ]). It uses the same chassis as the previous Mark 5 versions (A, A+, B, B+ and C). 15 The EVN will move towards diskshipping-less operation using either a FlexBuff or a Mark Turning to diskshipping-less operations would have many significant advantages. Stations NEXPReS was an e-Infrastructure project led by JIVE and funded by the European Union’s With more and more EVN stations acquiring and starting to use digital BBCs, and the VLBA The next step is to upgrade the EVN (or at least some of the stations) to 4 Gbps (disk recording) The EVN has not really discussed observations beyond 4 Gbps. However, one could envision 6. The FlexBuff wascally designed a at server Metsähovi with Finland a as big,very non-shippable part high-speed box of simultaneous of recording/playback. the hard NEXPReS The disks,Haystack project. Mark with ([ 6 clever It software system optimized is is towards being basi- developed at MIT operate at 32 Gbps (4 GHz bandwidth, dual polarization and 2-bit sampling). would not need to bother withdone conditioning, practically changing automatically, and results shipping ofavailable disk a in packs, real-time, significant transfers no sub-set packs could of would be need thestations to do EVN be not sent network have out that sufficient before would connectivity eachis (for session. be not example, Unfortunately, likely some the either KVAZAR that or e-shipping the willproject) Chinese become anytime stations). a soon. It viable option for the VLBA (i.e., for Global VLBI Apart from the enclosures, disk modules andthe-shelf a (COTS), custom-made and backplane, all it software is is fullyof open Commercial-off- 8 source. Gbps The recording Mark on 6 two comes diskdisk in packs, packs, two and two versions, a of one 16 which capable Gbps are version. mounted The in latter a version second records enclosure. onto four Seventh Framework Programme. The project successfullyaims concluded of on NEXPReS 30 was June to 2013. introducedistinction One an between of recorded e-VLBI and the element real-time into VLBI. all Althoughit this EVN now has operations, is not to quite certainly take happened feasible. in away Thus,e-VLBI practice, the simultaneously there even are at no 4 real Gbps. technical obstacles to doing3.3 disk recording Next and generation backends and recording systems switching to the exclusive use ofon RDBE, the a prospect regular of base doing has astronomicalalready VLBI become in at quite February 2 2012 realistic. and and 4 is In Gbps of now fact, fully 1 Gbps the operational. and VLBA Presently, the started the EVNhave limited current operates an 2 at plan Gbps array a is operation maximum where toobservations). a offer few Correlation 2 Gbps stations of (disk such still recording)the data observe in data has at 2015. rate been 1 means successfully Gbps Most oflimits tested and the likely using course the number we the that of rest projects will SFXC. the that at Increasing EVN canto 2 be the Gbps needs scheduled. total to (mixed cost However, the of increase mode cost running is its the relatively disk EVN. small compared pool which alreadybut there today is no firm plan(dual when polarization this should and be 2-bit implemented.(which sampling) This may and implies be a the one bandwidth case issue of also 512 here for 2 MHz is Gbps) at to some find wavebands. operations a above that common at the frequency higher frequency range of bands (22 telescopes and in 43 the GHz), EVN in particular capablein since of the the operating number past at years. 22 With GHz the (and third beyond) generation has of increased substantially the DBBC, the DBBC3 ([ Present status and technical directions of the EVN PoS(EVN 2014)031 M. Lindqvist 7 ]), developed and maintained at the JIVE has been used for ]), see below. 4 UniBoards can handle 16 stations at 4 Gbps. 7 10 5 more hardware. Another (less costly) possibility would be to use the ∼ ]) was a Joint Research Activity in RadioNet FP7 (a project supported by the 10 The SFXC software correlator ([ Uniboard ([ The main advantage using the software correlator approach is that it is fantastically flexible. As has been shown at this conference, the EVN is producing excellent science. This is of The maximum data rate for e-VLBI is currently 1 Gbps. Even if most EVN stations can operate The current SFXC cluster at JIVE can handle 13 stations at 1 Gbps. 16 stations at 4 Gbps It is easy to modify, improve,time extend, goes expand by. and One upgrade. should Furthermore, howeversystem. hardware not gets underestimate In cheaper the addition, as effort it need is toother make not hand, it very the into well JUC an suited will operational forThe be heavy disadvantages perfect lifting of for such the simple as JUC operationsmuch e-VLBI are (such harder at that as to 4 it develop standard firmware. Gbps. is 4 One not Gbps OnSFXC could nearly experiments). envision the and that as the JIVE flexible JUC. will as operate a 2 correlators, software both correlator the and it is 4. Conclusions course of fundamental importance andIn the order main to motivation for meet further theprogress. developments demands of of We the the have EVN. astronomers shown the insteps EVN already this is exists paper making today, that both use at much ofcomplement the of and the stations the driving SKA and as technical instrumentation at it JIVE. needed is With to being its take rolled unique out, capabilities, the the which next future will of the EVN is definitely looking bright. One board is roughly equivalent to the old MarkIV EVN3.5 correlator. The correlators at JIVE all EVN correlation since December 2012since (the then). old MarkIV It hardware has correlatorpossibility opened has to not up combine been novel used gating modesimaging and such by binning, as, using (practically) multiple mixed phase unlimited bandwidth centresmode. spectral correlation, (under resolution, pulsar development also gating, wide-field in real time) and a phased array European Commission under the 7th Frameworka Programme) generic led high by performance JIVE. computing TheUniBoard platform aim Correlator for was (JUC). radio to astronomy. create One application is the JIVE at 1 Gbps there are still importantUrumqi. stations that are The not main connected, notably limiting the factormany KVAZAR stations to stations and operate do beyond have 1 GbpsNetworks excellent (NRENs) is connections across thus Europe (10 the are Gbps). connectivity beingthat even upgraded The many though to a EVN National capacity stations Research of will 40/100Bandwidth and Gbps follow. on and Education Demand it As (BoD) is investigated likely which inwould is allow NEXPReS, being a the implemented customer EVN by such the could asneed NRENs. the make it, EVN e.g. use BoD to during of is request an a bandwidth e-VLBI service at session. that desired level when andwould where mean it a factor of Present status and technical directions of the EVN 3.4 e-VLBI FPGA based UniBoard correlator ([ PoS(EVN 2014)031 , , in , IVS 2010 , in . 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