Radio Frequency Interference Survey, Monitoring and Mitigation at GMRT

The GMRT has undergone a major upgrade that provides near seamless frequency coverage from ~ 100 MHz to 1500 MHz with instantaneous bandwidths of up to 400 MHz, using state of art technologies for the electronics, signal processing systems, and monitor and control systems. This wideband operation significantly increases the risk of Radio Frequency Interference (RFI) from sources external and internal to the observatory.  The wider frequency coverage invites many known commercial transmissions into the receiver band which can lead to non-linearity of the system. Also, modern computers and network equipment’s along with UPS and SMPS power supplies produce significant interference that can leak into the band of observation, in addition to that from common utility items like air-conditioner units and lighting equipment.

The first speaker will present the new sources of external RFI seen with the wideband receivers of the upgraded GMRT, quantifies their characterization and highlights the mitigation methods adopted for each case.  It discusses in detail about the RFI survey and monitoring techniques to locate power line interference, interference from wind power generators, industries and other sources of external RFI such as air traffic control, satellite interference, police wireless, digital TV transmission, leakage from cable TV networks,  and the efforts taken to co-exist with them.  Additionally, the various sources of internal RFI from electrical, electronic and network equipment, its characterization with standards adopted at the observatory, and the shielding solutions are presented, along with test results.  The presentation talks about the RFI shielding measures adopted for the design of a new laboratory building at the GMRT, which is enclosed in a Faraday cage with proper RFI shielding for doors and windows, electrical wiring, computer networks, and utility services entering the building.   

There are about 35000 Satellites are in space to provide voice and data service, navigation, GPS, weather, military and various space programs. These satellite footprints are larger to cover a wide area and produce interference to radio telescopes. These satellites are geo stationery, geosynchronous, low, and medium orbiting satellites whose locations and orbits have been characterized with the precise servo system of GMRT antennas.

The second speaker will present the novel technique to live with the satellite interference and the method of avoidance during the radio astronomy observation will be discussed with a live demo of the software to predict and avoid the satellite interference in real-time. The software tools provide a prediction of these satellite cross over with any scheduled radio astronomy observation, real-time location of the antenna beam with an adjacent line of site satellites on the sky and tools to post-process the old astronomical data for flagging the duration of satellite signal overlap or saturation.


About the Speakers:

Pravin Ashok Raybole, Engineer D joined the NCRA-TIFR in August 1995, acquired in Bachelor of Engineering (Electronics & Telecommunication) from Cusrow Wadia Institute of Technology,  Pune University and Diploma in Electronics and Radio Engineering (DERE), Cusrow Wadia Institute of Technology, DTE, Pune, Maharashtra. He has 25 years of work experience at the GMRT observatory.  His professional experience is in Radio Frequency Interference (RFI) mitigation, RF over fibre and optical computer networking. He has presented papers at RFI 2010, RFI mitigation workshop, Groningen, Netherlands, URSI 2017 at the URSI General Assembly and Scientific Symposium (GASS), Montreal, Canada and at the IEEE International Microwave and RF Conference 2019, IIT Bombay, Mumbai.

Santaji Niwritti Katore, M.Sc. (Physics), Scientific Officer 'D' at GMRT. He has joined GMRT in August 2000 as Telescope Observer and operated the telescope for 13 years. After 2013, he started working as a software developer for various subsystems of the GMRT. Currently, he is involved in the projects like automated telescope scheduling, satellite RFI mitigation, servo-mechanical system data analysis, primary beam measurements, a web-based monitoring and observing tools and control and monitor system etc.