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Tuning your "ears"

The frequencies around 1420 MHz are especially interesting to look at because of their proximity to the "water hole." Also, because of the importance of this part of the spectrum to radio astronomy, by international agreement no one is allowed to produce any broadcasts between 1420 MHz and 1427 MHz. Because of this ban, it's an especially quiet part of the spectrum. Let's take a closer look at what this means. 

 

What exactly are we looking for? As mentioned previously, the most efficient way for an alien race to get noticed would be to concentrate all the radio energy in a very narrow frequency signal. If your radio receiver is "sloppy" and can only look at broad ranges of frequencies, the narrow signal will get swamped by all the unwanted signals around it -- even if that signal is very strong.
Imagine a person with a loud whistle in a huge noisy crowd. The whistle has a very specific frequency or pitch. If you were just using your ears, which pick up a wide range of pitches, the noise from the crowd would mask out the whistle. On the other hand, what if your ears were tuned to listen only for the pitch of the whistle? You wouldn't hear much of the crowd noise because most of it wouldn't occur at the pitch you are "tuned" to. But the whistle would come through loud and clear. In the same way, the SETI@home listens in many precisely tuned channels (or frequencies) for signals that are significantly "above the noise." With your help, SETI@home does one of the most detailed and finely tuned searches ever attempted. Your computer will "listen" to the sky for signals as narrow as 0.07 Hz.

 

"SETI: The Radio Search"

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