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RFI Mitigation for Electronic and Natural SKA Environment Philip Kibet Prof HC Reader Stellenbosch University SKA Postgraduate Bursary and Postdoctoral Fellowship Programme2008Philip Kibet
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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
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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
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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
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Sparking noise Contd. Radiated noise energy, which decays with frequency, beyond 200MHz SKA Postgraduate Bursary and Postdoctoral Fellowship Programme 2008 Philip Kibet
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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
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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
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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
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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
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Cat -7 cables evaluation contd. Typical results from SOLT SKA Postgraduate Bursary and Postdoctoral Fellowship Programme 2008 Philip Kibet
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Cat -7 cables evaluation contd. Typical results from TRL SKA Postgraduate Bursary and Postdoctoral Fellowship Programme 2008 Philip Kibet
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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
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