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FUTURE DIRECTIONS ON THE VLBA

FUTURE DIRECTIONS ON THE VLBA. Craig Walker National Radio Astonomy Observatory. IVS General Meeting Ottawa, Feb 2004. OUTLINE. Mark5 High frequency upgrades Spacecraft tracking Ka band receiver EVLA Receivers LO/IF (bandwidth, fibers etc) Correlator New Mexico Array

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FUTURE DIRECTIONS ON THE VLBA

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  1. FUTURE DIRECTIONS ON THE VLBA Craig Walker National Radio Astonomy Observatory IVS General Meeting Ottawa, Feb 2004

  2. OUTLINE • Mark5 • High frequency upgrades • Spacecraft tracking • Ka band receiver • EVLA • Receivers • LO/IF (bandwidth, fibers etc) • Correlator • New Mexico Array • EVLA/NMA/VLBA Integration • Impacts on Geodesy and Astronomy

  3. MARK5 ON THE VLBA • Trying to obtain funding of about $3M • Need 36 units • 12 station units (VLBA, VLA, GBT) • 24 correlator units • Need disks for about 400 station days at 1Gbps • Prefer Mark5B to allow 1Gbps. • VLBA formatters can only do 512 Mbps • Current playback max 256 Mbps/station • Will read 512 Mbps/station with Mark5B • 1 Gbps on 10 stations using 20 station inputs. • Total cost about $3M • Includes about $1M in hardware for interfaces etc.

  4. HIGH FREQUENCY UPGRADES • Surface improvements • Refigured subreflectors using Faro Arm (Pie Town done) • Holography and panel resetting • Multiple position holography system to separate main reflector from subreflector • Receiver improvements Upgrade to new style amplifiers at 22 and 43 GHz (Not yet funded)

  5. SPACECRAFT NAVIGATION • Project to investigate using VLBA for determining spacecraft positions • Alternate to Delta DOR • Does not require special spacecraft signals • Use phase referencing techniques to resolve phase ambiguities • Can deliver positions and phase/delay totals • Eventually would need Ka band

  6. EVLA (Expanded VLA) • Phase 1 – In progress • New correlator • (8 GHz, dual polarization) • New receivers • (1-50 GHz full coverage) • Fiber optics (96 Gbps) • Phase 2 – Proposed • New Mexico Array (350 km, 10 antennas) • E Configuration

  7. NEW MEXICO ARRAY • Ten antennas • 8 new, 2 VLBA (PT,LA) • Baselines to 350 km • Ten times VLA resolution • Full bandwidth of EVLA • VLBI at reduced bandwidth • Provides short spacings for VLBA

  8. FREQUENCY BANDS

  9. VLBA LO/IF OPTIONS 1: 256 MHz: Use current formatter, BBC’s etc. • Would probably continue to use VLBA correlator • No cost per VLBA station beyond Mark5 • NMA proposal has 512 Mhz (2 Gbps) 2: 1 GHz: Sample VLBA 500 MHz IFs • New samplers, formatter and data transmission • Keeps VLBA LOs and IF converters • Estimated cost: $50k per station 3: 4 or 16 GHz: Use EVLA LO/IF system • Must replace much VLBA IF and maybe LO systems • Estimated cost for 16 GHz: $550k per station Cost estimates are rough

  10. REAL TIME DATA TRANSMISSION • EVLA uses optical fibers for 96 Gbps • 12 optical channels at 10 Gbps each • EVLA27 uses NRAO installed fibers • NMA will use local, rural phone company fibers • Cost much lower than large companies because of very different business model • NRAO provides all electronics, lasers etc. • VLBA – desire but no definite plans • High bit rates are likely to be very costly • All sites reasonably close to existing fiber • Real time correlation prevents multiple pass processing

  11. CORRELATOR OPPORTUNITY • EVLA WIDAR correlator can handle VLBI data • This is a nearly-no-cost option except interfaces and delays • Could be from recordings but real-time much preferred • EVLA correlator has extra station inputs • Natural breaks at units of 8 stations (32, 40, 48) • VLA has 27. NMA + VLA has 37. • Each 16 GHz station input can take: • 2 stations at 4 GHz each (16 times upgraded VLBA bandwidth) • 4 stations at 1 GHz each (4 times upgraded VLBA bandwidth) • EVLA correlator can also be the next VLBA correlator • Expansion only required for >4 GHz on all stations at once • Operationally and psychologically unites the instruments

  12. IMPACTS ON VLBA GEODESY/ASTROMETRY • Wider bandwidths (Mark5 EVLA) • Higher SNR, weaker sources, faster schedules • Higher frequencies • Wider spanned bandwidths • Less RFI, less ionosphere • Can test now on VLBA • Rapid turnaround if go to real time • Issue: – How to measure ionosphere at high freq. • No currently planned dual frequeny capability

  13. GEODETIC CONTRIBUTIONS TO VLBI ASTRONOMY • Accurate models make phase referencing possible • Any improvements useful • Phase referencing used by about half of VLBA projects • External ionosphere and troposphere • GPS ionosphere models • Currently in regular use for VLBA • Future: Finer grids, 3D • GPS troposphere: About to test on VLBA • WVR: Testing on VLA and mm arrays • Denser, more accurate source catalogs

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