General Information

SETI League Glossary

This glossary of terms commonly used in SETI discussions is a work in progress, started by David Woolley on the open SETI email discussion list. Initial glossary entries are copyright © 1998 by David Woolley. Members are invited to contribute their own working definitions of other specialized terms which they encounter in SETI discussions. Email your glossary contributions to info_at_setileague_dot_org.

Other specialized SETI terms require a paragraph to a page to more fully define. Be sure to check the Website Alphabetical Index for terms not listed here, and see the SETI League FAQ's and General Information sheets for further definitions.

• bin - FFT and similar algorithms split the frequency range up into chunks, typically of fixed length; these are bins.
• Doppler - change in apparent frequency of a wave due to motion of source or receiver.
• FFT - Fast Fourier Transform - a specific algorithm, but used to indicate any algorithm attempting to determine the power versus frequency graph for a signal.
• frame - frame of reference - in this case, defines the zero and axes for defining a velocity.
• GUI - graphical user interface (Windows, Macintosh, X-Windows, etc.).
• inertial - not being accelerated by any force, including gravity (note that orbiting planets are accelerating towards their sun).
• integration - adding up multiple consecutive samples as the noise (measurement error) will grow as the square root of the number but the signal will grow linearly.
• ISM - insterstellar medium
• local oscillator - microwave signals are shifted down in frequency by combining them with a locally generated signal in such a way that the difference in the frequencies is generated. The local signal is generated by the local oscillator. In project Argus type systems, the frequency is shifted from around 1420,000,000 Hz, to somewhere around 1,800 to 20,000 Hz (centre). There are many reasons for doing this, but if it weren't one would still need an accurate local references of the same precision, which needs to be significantly better than the bin width in 1420,000,000 Hz.
• power, frequency, bandwidth, voltage - assumed common knowledge.
• power versus field - like power and voltage in an electrical system.
• T1 - US standard for carrying 24 telephone circuits digitally at a little over 1,5 million bits per second.
• transit time - the time it takes the earth's rotation to move a source from one edge of the antenna beam to the other.
• waterhole - the frequency range in which the earth's atmosphere doesn't absorb a lot of the signal.
• V.34bis - specification for a modem operating at up to 33.6 thousand bits per second.

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