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There are two types of radio frequency interference (RFI) that can be easily
detected and eliminated. The first type of interference is called "always on", meaning that every result file in the frequency band has the signal detected. This happens at 5 frequencies in the SETI@home band: 1418.75, 1419.00, 1420.00, 1421.00 and 1421.25 MHz. Many of these signals are deliberately introduced by either the instrumentation or the software, which record and process the data. The other type of RFI only appears for short periods of time in the data. This is found by comparing the length of time that a set of signals in a single frequency range are detected and comparing that to the length of time that the telescope beam looks at a patch of the sky. This is less common than the "always on" RFI but must be eliminated in order to find the true characteristics of the background sky and to improve the quality of signal candidates selected for further analysis. See Newsletter #8 for more details on RFI removal procedures. |  Sample frequency histogram of spikes with RFI at 1419, 1420, & 1421 MHz  Same histogram with RFI removed |
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