1. RFI Mitigation for Electronic and Natural SKA Environment Philip Kibet Prof HC Reader Stellenbosch University SKA Postgraduate Bursary and Postdoctoral Fellowship Programme2008Philip Kibet

2. Introduction RFI investigation and mitigation on SKA system Part I RFI implications due to sparking noise from power-lines and electric fences Part II CAT7 cables for SKA system SKA Postgraduate Bursary and Postdoctoral Fellowship Programme 2008 Philip Kibet

3. Power line noise Power line RFI caused by corona and sparking 90% of RFI caused by power lines is due to sparking Sparking noise - complete breakdown of air insulation between two electrodes RF energy up to & beyond 1GHz Power line acts as an antenna SKA Postgraduate Bursary and Postdoctoral Fellowship Programme 2008 Philip Kibet

4. Sparking noise measurement Spark-gap noise in High Voltage Lab and short power line Attached to power-line 7m above ground. 4mm & 6mm gaps considered Frequency spectrum and time-domain characteristics of sparking noise Zero-span settings of SA yields time- domain data Measured results take into account used antenna transfer function Antenna polarization matters: vertical due to spark-gap, horizontal due to line SKA Postgraduate Bursary and Postdoctoral Fellowship Programme 2008 Philip Kibet

5. Sparking noise Contd. Radiated noise energy, which decays with frequency, beyond 200MHz SKA Postgraduate Bursary and Postdoctoral Fellowship Programme 2008 Philip Kibet

6. Sparking noise Contd. SKA Postgraduate Bursary and Postdoctoral Fellowship Programme 2008 Philip Kibet Purpose – identify profile of sparking noise spectrum – propagation distance direct from source & along line – variation of line voltage effect Corona to be considered

7. High Freq Dish antennas Signal Transport CAT-7 (with ARJ45) cables to be used between aperture array antenna tiles & screened processing areas (Bunkers) SKA Postgraduate Bursary and Postdoctoral Fellowship Programme 2008 Philip Kibet Bunker Aperture Array s CAT- 7 cables Good signal integrity Low emissions, crosstalk High bandwidth & non- dispersive transmission

8. Cat -7 cables evaluation CAT-7 cable system incorporating 20 m CAT-7 cables, balun transformers, and ARJ45 connectors 1AB 1AO SKA Postgraduate Bursary and Postdoctoral Fellowship Programme 2008 Philip Kibet Cable Sheath Conductor pair Foil pair screen Braid screen

9. Cat -7 cables evaluation contd. Calibrated VNA used from 30 MHz-1.5 GHz SOLT - entire cable system performance TRL- cable performance SKA Postgraduate Bursary and Postdoctoral Fellowship Programme 2008 Philip Kibet

10. Cat -7 cables evaluation contd. Typical results from SOLT SKA Postgraduate Bursary and Postdoctoral Fellowship Programme 2008 Philip Kibet

11. Cat -7 cables evaluation contd. Typical results from TRL SKA Postgraduate Bursary and Postdoctoral Fellowship Programme 2008 Philip Kibet

12. Further Work…. Further measurements Model spark-gap noise Inter-dish interference Determine ways of minimizing these emissions SKA Postgraduate Bursary and Postdoctoral Fellowship Programme 2008 Philip Kibet