RFI excision

Radio Frequency Interference (RFI) at Molonglo is predominantly due to mobile handsets, with at least two handset frequencies in the observing band, and with a bright base-station tower just above the band.

phonecall.qsoThe figure above shows a mobile phone call in the observing band (lower panel) as strong slanted lines. Flagging these data through their effect on the kurtosis of the voltage histogram, allows the phone call to be blanked and the much weaker quasar calibrator to show through.

Molonglo is in a particularly interesting position to deal with RFI, because we have 352 independent antennae in an array. Triangulation can be made to local sources, and their effects removed from the digitized voltages directly. The key to this is our realtime processing capability with the GPU correlator.


The figure above shows two phone calls standing out quite distinctly from the usual noise in which the signal lies. Image credits : Andrew Jameson, Shivani Bhandari, Vivek V Krishnan.