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Broadband Tests and Hardware Design for eVLBI

This document discusses the goals and specifications for broadband eVLBI, including hardware design and testing. It also explores the possibility of using existing correlators as templates. The document outlines the channelization options and the decision-making process for the future system. The goal is to prototype a new astronomy capability and test the concept prior to implementing a new EVN correlator. The timeline includes the availability of eMERLIN interfaces and the expected completion of the prototype at Onsala station and the overall broadband demo.

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Broadband Tests and Hardware Design for eVLBI

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  1. Broadband TestsJohn ConwayFABRIC F2F-2 Poznan, Sept 25th 2006 • Month 7 PC-EVN demo • Goals for broadband eVLBI • Specification and design of hardware for Onsala-MERLIN demo. • Procuring 10Gbit/s Onsala link. • Use of Onsala FABRIC resources manpower/money – in project context

  2. Month 7 Demo • EU forced test to demonstrate/re-establish a baseline PC-EVN performance – soaks up contributed manpower for us. Have now got an (almost) working PC-EVN at Onsala. • Scheduled for Friday Oct 20th. Need to start testing NOW • Part 1 – At 6cm, 256Mbit/s, record to disk at On and Jb. Then transfer to JIVE. Convert to Mk5 input and correlate. Should be easy...done several year ago. Who is ensuring this happens at JIVE ? • Part 2 – At 1.3cm, Mh does ’remote recording’ to PC disk at JIVE. Jb records to disk, later transfer, translate at correlator for fringes. I

  3. FABRIC broadband goals-1 • What are we trying to do???? A prototype future eVLBI production system? • Will it also do disk recording or just real time?? Major decision between PC-based or FPGA routes. • Ideally must service a future EVN correlator which does not exist – can we guess its channelization? • Meanwhile we do have MERLIN and LOFAR correlators – maybe we should use them (esp MERLIN) as template.

  4. FABRIC broadband goals-2 • Research project in distributed correlation, a part of the JRA but presently more useful conceptually to seperate from Broadband part. • Channelisation. Present system - many tunable filters and parallel bits streams. Old reasons, tape track limit, geodesy no longer valid? eMERLIN, eVLA one thick BW. Forget past start from scratch? To minimise complexity a few chanelisation modes only for transmitter? No specific ’spectral line modes’? • No of bits. eVLBI without dark fibre (unlike eMERLIN and LOFAR) is still transmit channel limited. Do RFI filtering at station end and just transmit 2bit/sample? • Must decide above issues SOON/TODAY to define exact specifications of what we will build!!

  5. FABRIC broadband goals-3 • No recording, FPGA technology is the way we go???? • iBoB ADC does 8bit and can digitise at Nyquist rate either 1pol of 1GHz BW or 2pol of 512MHz BW. • Transmitter wil lhave smart RFI rejection and outputs 2bits/sample. ’Notch out’ filtering and outputs a limited number of digitally filtered bandwidths. Say four corresponding to 1024MHz, 512,256,128 MHz? ( 4 to 1 Gbit/s). • Lower limit set by spread of OH maser lines (112MHz) , and whether network costs for 1Gbit/s are negligble when operational. • At input to correlator further channelisation may be done prior to high spectral resolution correlation of multiple narrow channels.

  6. Interim Goal- EVN stations to eMERLIN • Can prototype a new astronomy capability + test out concept prior to new EVN correlator. • In general seems reasonable when planning for EVN2010+ – converge on eMERLIN specs BW and freq ranges for L,C,K, (+add other bands) • Operational system at L-band. 1 iBoB 512Hz x 2pol giving 4Gbit/s • Could expand to have at C and K bands 2 iBoBs, sampling 1GHz of spanned BW at each pol, 2bit sampling, giving 8Gbit/s - get sqrt(2) sensitivity of eMERLIN – can eMERLIN obs 2GHz BW same time as 1GHz external.

  7. UV Coverage Left. UV (km)– Coverage for 6 stations MERLIN + Onsala + Wb1 at dec +40deg Right . UV (lambda) shows result of MFS Multi-frequency thesis for L-band 1300-1800MHz (4Gbit/s data rate). Other possible combinations MERLIN + Onsala only, or include Bonn or Irish telescope.Not a competitor to full EVN or EVN+MERLIN, which even just in Europe has three times the resolution and 16 stations.

  8. Parameters of 4Gbit/s Demo • Dual Polarization, 512MHz spanned BW, Nyquist sampled, 2bit giving 4Gbit/s. • Correlate versus eMERLIN 8bit sampled data (16Gbit/s)- potentially has same sensitivity as full 16Gbits/s but no RFI protection – less important on long baselines and can ’notch out’ any strong RFI at Onsala?? • Would be very useful L-band production system, with 25m connected to MERLIN (SEFD=370Jy) . Initial test. • The C and K-band eMERLIN system normally works at 3bit sampling, 2GHz spanned BW and 24Gbit/s, can it be switched to the 16Gbit/s, 8bit sampling mode for test • Option 1 – test at K-band, no new fibre of LO system needed. • Option 2 – Fibre to 25m, and broadband L and C band LO system. Better for operational system.

  9. Timeline • DOW has ’Prototype at Onsala station’ and ’overall broadband demo’ by Month 23 (Feb 2008). • Also has eMERLIN interfaces available by Month 30 (Sept 2008) – inconsistent. • eMERLIN prototype correlator arrives end of 2007. Very hard to meet Month 23 fringe deadline • Have DAR at Onsala by March 2008, software integration and transmitting data from 25m to Jb at 4Gbit/s by that time. By Sept 2008 fringes?? • Hire Onsala manpower by June 2007 for 1+ year????

  10. Link Progress • Discussions through SUNET on upgrading our 1Gbit/s to 10Gbit/s (they will negotiate with vendors for us, still waiting for a cost but expect to get this and order soon). • Two options, link all the way into Chalmers in Gothenburg (55km) or connect to trunk in Kungsbacka. • Not absolutely needed until test in Month 23, Febuary 2008. Purchase depends on price falling/depreciation. • Meanwhile Mh has 10Gbit/s already. Traffic goes through Stockholm just like Onsala data– hence can test most of the route in Mh-Jb tests, all except internal Swedish part.

  11. OPTOSUNET • SUNET historically double BW every year. OPTOSUNET is successor to GIGASUNET. • Dark fibres leased for a 40Gbit/s backbone- fully implemented end of 2006 • Most universities connected at 10Gbit/s • Allow both IP and dedicated point-to-point wavelengths (cost stucture?) • For international transmissions go through NORDUNET

  12. NORDUNET Staus as of April 2006, signals go through Stockholm to rest of world, nor sure a direct connection via Copenhagen possible – NORDUNET congress Sept 25th -30th in Göteborg

  13. Use of Onsala Resources • Onsala has from EU 1 man-year and 10kEuro for Equipment – how to use that? • Option 1 – Recruit electronic engineer help work on iBoB with Mh. Ex Intl Masters student now at Berkely Wireless research group. • Option 2 – Use to broadband the 25m, fibre plus new IF system. Software control of iBoB. Testing of network.

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