A radio signal's "power" is its strength relative to noise. We don't expect extraterrestrial communications to be high-powered after crossing interstellar distances (although it is theoretically possible). Instead, high-powered signals are typically created by close-proximity RFI or by injected test signals. SETI@home uses power histograms to examine power distributions for anomolous patterns and other outliers.
Once known RFI is removed from our data, most high-powered signals should disappear from these distributions. Above are two sample power histograms taken from signal spike data recorded on May 24, 2000. The histogram on the left plots all spikes recorded on that day; the one on the right ignores artificially injected spikes at 1418MHz, 1420Mhz, and 1421Mhz.
 click to enlarge |
 click to enlarge |
Above are two sample power histograms taken from signal spike data recorded on May 24, 2000. The histogram on the left plots all spikes recorded on that day; the one on the right ignores artificially injected spikes at 1418MHz, 1420Mhz, and 1421Mhz. Also viewable are frequency histograms from the same day.
A detailed discussion of power histograms can be found in Newsletter #6—Distinguishing Possible Extraterrestrial Signals From Noise and RFI.
Copyright ©2001 SETI@home