Real-time RFI filtering for uGMRT: Overview of the released system and relevance to the SKA

Abstract

Radio Frequency Interference (RFI) of impulsive nature is created by sources like sparking on high-power transmission lines due to gap or corona discharge and automobile sparking, and it affects the entire observing frequency bands of low-frequency radio telescopes. Such RFI is a significant problem at the Upgraded Giant Metrewave Radio Telescope (uGMRT). A real-time RFI filtering scheme has been developed and implemented to mitigate the effect on astronomical observations. The scheme works in real-time on pre-correlation data from each antenna and allows the detection of RFI based on median absolute deviation statistics. The samples are identified as RFI-based on user-defined thresholds and are replaced by digital noise, a constant or zeros. We review the testing and implementation of this system at the uGMRT. We illustrate the effectiveness of the filtering for continuum, spectral line and time-domain data. The real-time filter is released for regular observations in the bands falling in 250–1450 MHz, and recent observing cycles show growing usage. Further, we explain the relevance of the released system to the Square Kilometer Array (SKA) receiver chain and possible ways of implementation to meet the computational requirements.