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Radio Frequency Interference Mitigation

-- | May 25, 2014

Question:  We learned this weekend that a wealth of modern conveniences, from a dog blanket to car keys to digital cameras to trinket fans can cause crazy EM radiation that will register on readings from the GBT and other radio telescopes. While some ground-sourced EM radiation is recurring and predictable, many of these sources are active only when operated. While you can track down many sources with your specially-equipped truck (EMITT?), a more all-encompassing and passive approach might benefit the astronomers. Would there be value in surrounding the telescope with smaller antennae that would pick up and triangulate stronger EM signals and form a kind of noise-canceling knowledge that could be used to mask the received signals? Or would there perhaps be value in surrounding the telescope with an enormous Faraday-cage fence? Of course, the trinket fan demonstrated that some signals are not blocked by a Faraday cage.  — Daniel

Answer:  The separate RFI measurement system would certainly help with identifying sources of RFI, and would function as a real-time measurement system.  An array of RFI measuring antennas, though, likely would not provide much location capabilities as the wavelengths that sources of RFI emit at are quite long, making the triangulation capabilities of an array rather poor.  As for placing a Faraday cage around a telescope, the problem would be in the fact that it would interfere with the reception capabilities of the telescope.  The fact is that we are facing a more crowded RFI environment in radio astronomy, which has forced us to concentrate of ways of making our telescope reception patterns more efficient (i.e. better concentrated on measuring the astronomical sources, and *not* sources of RFI) and monitoring known sources of RFI.

Jeff Mangum