small logo SETI League Technical Manual -- Block Diagram

Signal Analysis Computers

Copyright © 1999 by H. Paul Shuch, Ph.D.
Executive Director, The SETI League, Inc.
PO Box 555, Little Ferry NJ 07643
email n6tx @

Even the simplest of today's personal computers is thousands of times more powerful than the ones NASA used to put men on the moon. Of course, the objective of SETI is not to reach the moon, but rather to reach much farther out into space for intelligently generated signals. To do so, we employ a technique known as Digital Signal Processing, or DSP.

The 22 kHz audio signal applied to the computer's sound card is a rather narrow bandwidth, which even a 486-class computer can analyze in real time, with excellent resolution. The typical DSP program chops the received audio band up into 2048 individual channels, each about 10 Hz wide, analyzing and displaying all those channels simultaneously, in real time. Thus, the computer turns the SETI station into a 2048-channel receiver.

The required software, developed by SETI League members, typically runs under the Microsoft DOS or Windows operating systems. It is shareware, offered at low or no cost to all participating SETI league members via the Software pages of The SETI League website. Its job is to identify signals which exhibit the hallmarks of artificiality, characteristics which distinguish it from natural phenomena, and then to help determine whether those characteristics might have come from some terrestrial source.

Our civilization pollutes its own radio environment, so we need to sift through any detected signals rather thoroughly in order to rule out manmade interference from our own transmitters, aircraft, spacecraft and orbiting relay stations. For example, the first candidate signal received by a Project Argus station, in May of 1996, turned out to be interference from a classified military satellite. Determining this would have been challenging for the human observer, but was a trivial identification task for our computers.

More SETI computer information may be found in the Software chapter of The SETI League Technical Manual.

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