1. MeerKAT Lightning Protection, Earthing and RFI Mitigation 01 December 2010 Dr. Gideon Wiid Post-Doctoral Fellow Host: Prof. Howard Reader

2. Engineering Search: Nearby Galaxies and Pulsars Galaxy nearby: Cape Town Pulsar serviced, no more timing problems

3. Acknowledgements EM research group at SU: Prof. Howard Reader, Joely Andriambeloson, Dr. Braam Otto, Dr. Paul van der Merwe, Philip Kibet SKA SA Teams for support in measurements: Japie Ludick, Richard Lord, Carel van der Merwe, Luyanda Boyana, Siya Tshongweni NRF and SKA SA Sponsorship TESP funding for equipment

4. RFI Background Reverberation Chamber and cable transfer impedance Lightning Protection RFI Mitigation Earthing Menu

5. Contrary to popular belief: RFI ≠ Black magic NB: Electrons and Energy Opposite charges attract Electric field in between two polarities Electron experiences force in E-field Background to RFI ≠ RFI

6. Free electrons – sneaky little rascals Always takes the path of least resistance! Very Excitable – especially with time-varying E-field applied Electron E-field lines: stationary vs. moving Background – Electrons

7. Background – Making Waves

8. Joely Andriambeloson – Transfer impedance of cables Reverberation chamber – Stirring or mixing waves Characterise avg or max Confirm field uniformity Standard radiator Compare to calibrated data Compare to GTEM Future: OATS Reverberation Chamber

9. Cable transfer impedance vs shielding effectiveness 15 SKA cables and metal braided sheath GPS cable compromises Shielding chamber Influence on overall shielding effectiveness Cable Transfer Impedance

10. Elevation Motor assembly Lightning current levels Bonding efforts Path of least resistance Dirt road vs highway Traffic jam! Lightning Protection 1

11. Rogowski coil used for current measurement (pool noodle) Structure currents spread out LDC and Elevation currents concentrated Bearings grease changes impedance FEKO simulations currently busy Lightning Protection 2

12. Impedance: Z C = 1/jωC Z L = jωL ; HF Currents more concentrated Lightning Protection 3

13. Azimuth bearings Shoes and LDC conductor Misaligned 2 vs 4 FEKO during PhD Measurements Nov. 2010 RFI Mitigation 1 - Shoes

14. LDC two extra connections Clamped on other LDC and plate Measurements inside and outside Current levels outside higher on avg for 4 vs 2 connections Less current toward inside of pedestal Path of least resistance! RFI Mitigation 2 - Measurements

15. RFI Mitigation 3 - Shielding

16. Chiller plant no earthing philosophy – floating Cables going through to pedestal interior Possible path for induced currents Consider optimal earthing options Chiller Plant Earthing 1

17.  No redirection of current  Shunted connection redirects current Chiller Plant Earthing 2

18. Conclusion Reverberation chamber method – relatively quick for testing cable shielding effectiveness or transfer impedance Lightning protection measures can be incorporated at MeerKAT design stage Elevation assembly might be reconsidered Pedestal RFI can be mitigated with correct shielding and cable terminations Correct earthing and terminations will aid in redirection of induced currents Electrons are sneaky!

19. T H E E N D Thank you for your time Any Questions? Veni, Vidi, Velcro ( I came, I saw, I stuck around )