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RFI Characterisation of Karoo Array Telescope Structure

RFI Characterisation of Karoo Array Telescope Structure. P. Gideon Wiid (PhD) Howard C. Reader Riana H. Geschke Stellenbosch University December 2008. Where do I fit in?. RFI - Radio Frequency Interference Extremely low RFI needed

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RFI Characterisation of Karoo Array Telescope Structure

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  1. RFI Characterisation of Karoo Array Telescope Structure P. Gideon Wiid (PhD) Howard C. Reader Riana H. Geschke Stellenbosch University December 2008

  2. Where do I fit in? • RFI - Radio Frequency Interference • Extremely low RFI needed • Earth-bound RFI, e.g. direct and indirect lightning strikes • Scale model measurements • Computational modelling Fig 1: Lightning strike

  3. What am I doing and how? Correctly define and minimise RFI on KAT structure: • Lightning policies – RAO sites • RFI measurements – XDM @ HartRAO • CEM Modelling and Measurement – KAT scale models • MoM w.r.t. lightning, shielding • Result analysis for RFI minimisation Fig 2: ADM design (June 2008)

  4. What have I done? 1 • Site Visits to: • Astron, LOFAR & Westerbork in Netherlands • Jodrell Bank & Manchester University in UK • Shielding of enclosures • Measurements at HartRAO on XDM • Importance of loops Fig 3: Westerbork and HartRAO Observatories

  5. What have I done? 2 • 2nd Model - 1/40th scale as per XDM • Focus: structure, conduit and soil • CADFEKO and CST verified by measurement • Memory and license limitations • Eskom load shedding • CHPC runtimes 4 days, 1 day • Towards ADM for KAT-7 • Specific concerns re RFI on ADM Fig 4: XDM model with saltwater

  6. What have I done? 3 • 3rd 1/20th Scale model – Willem Esterhuyse • June 2008 ADM KAT-7, simplified • Measurement – anechoic chamber • Geometry replicated in CADFEKO • CHPC runtimes / unknowns • CADFEKO verified by measurement • MoM investigations: lightning, shielding Fig 5: ADM Scale Model

  7. What have I done? 4 • Indirect lightning strike – EM plane wave • Direct lightning strike – current injection • Consider LDC, shielding • Electric field strengths • Current densities • Runtimes / file-sizes • CHPC and SU HPC Fig 6: Excitations on ADM model with LDC

  8. What have I done? 5 • EM Plane Wave • Current density • Magnetic flux cutting closed conducting loop • Top & bottom struts “hot” • Other positions • Edges “hot” • Shadowing • Bearings Fig 7: Current densities on dish struts

  9. What have I done? 6 • Current injection • Current distribution struts • Injection source loop influences levels • Shielding – top closed • Raised structure: “hot” • Cables entering: “hot” • Partial shields for cost • Feedback to SKA Fig 8: Electric field around and inside structure

  10. Where am I going? • Project plan: 2009 • CADFEKO Investigations: • Lightning protection over bearings • Pedestal shielding, earthing interfaces • Result analysis: cost-effective RFI solutions • Feedback to SKA offices, influencing design

  11. Confucius says • Confidence built for CADFEKO usage • E-fields, Current density • Shielding, earthing interfaces • LDC layout and design • LDC over bearings • Cost-effective solutions

  12. Conclusions • Confidence built for CADFEKO usage • E-fields, Current density • Shielding, earthing interfaces • LDC layout and design • LDC over bearings • Cost-effective solutions

  13. Are we done yet? Whether you believe you can do a thing or not, you are right. - Henry Ford Acknowledgements • SA SKA for bursary and travel grants • Eskom TESP for bursary grants • CST for use of Microwave Studio • EMSS for CADFEKO license and usage • Mel van Rooyen at EMSS for CADFEKO support • Willem Esterhuyse for enormous mechanical insights in scale model • Prof. DB Davidson, Danie Ludick and Evan Lezar for help in setting up simulations and CADFEKO on CHPC and SU HPC • CHPC and SU HPC for usage of facility

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