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"If there were thousands of amateur
systems (there are only a few at present), and there were a few civilizations
with transmitters a million or so more times more powerful than the typical
transmitter, an amateur system just might happen on a detectable signal
first." -- Dr. Frank Drake, cited in Omni |
For workers in the field, SETI has periods of extreme excitement. SETI also provides moments of satisfaction in a job well done, even when a search comes up empty. In some ways SETI can be a solitary and laborious activity. Some aspects of SETI data analysis can fatigue humans to the point where errors occur and signals might be missed. For this reason, we try to use several students to assist in analyzing the data. Students performing graphical FFT analyses should probably limit this activity to only an hour at a time. Students have two methods to screen data: (1) Using CoolEdit (which we use most often) or GoldWave alone, and watching for patterns in the spectrogram that might indicate signals, and (2) using SETIEasy, a computer program that uses multiple FFTs of varying length to search for unusual noise distributions in the data. This page describes the screening of data in general terms. Click one one of the following to read the page describing the use of CoolEdit in data screening, the use of GoldWave in data screening, or the use of SETIEasy in data screening. We appreciate the help of all the students in this endeavor.
The ASRG uses computer algorithms to scan all of the data collected from the radiotelescope. The screening at the radiotelescope for signals might miss unusual signals not programmed into the computerized search (the initial data collection and screening is accomplished with CoolEdit 2000 and the Spectral View function, and a cluster of computers running a version of SETIEasy). The algorithms search mainly for monochromatic continuous wave (CW) beacons with a Doppler-induced frequency drift. Pulsed signals and signals with low frequency modulation can also be detected if their intensity is sufficiently high. Students examine selected data files for evidence of signals that were not programmed into the search. The process of screening data is a simple one for students.
ASRG members record signals from the remote radiotelescope on disks and transport the data to the lab. The data are compressed into audio-formatted files, most of which are 5, 15 minutes or one hour long, and placed on the server so they can be screened. Files with names ending in utc_*.wav, where * is a number, are 15 minutes long (about 7 Mb) for easier downloading on telephone lines. Files with names ending simply in utc.wav are one hour long (about 28 Mb). Data are pre-screened at the radiotelescope site using an algorithm that detects large signals right away. The screening by students for intermediate-intensity signals involves calculating the FFT (fast fourier transform) of the data repeatedly over time, which can be done by shareware programs like CoolEdit (which we use most extensively for its sensitive spectral analysis capabilities), FFTDSP, Goldwave, or other programs. Using such programs, a file is played and displayed as a spectrogram. It is the task of the students to watch the spectrogram for possible "hits." A typical interference signal will be either a continuous or repeating thin line, as in the examples are shown below. These signals are "birdies" generated inside the equipment, or are other known interferences identified in our computers' Known Interference Log. (If they were unknown signals, the file would not have been posted until AFTER the signal had been confirmed by other Project Argus stations.) After checking a file, update the post on U Kentucky ASRG SETI about the file you analyzed, or if you found a suspicious signal (remember, it is probably interference), post a reply to the data files discussion group on U Kentucky ASRG SETI server so more extensive analysis of the data and signal can be undertaken. (N.B. SETI League protocol does not permit anyone to share any information about suspicious signals with anyone outside the established League channels, in order to prevent hoaxes and false alarms.)
So, these are the basic steps:
Read this page thoroughly, download a spectrogram program like CoolEdit or GoldWave if you do not already have one, set up the spectrogram, download a file from the server, post an In Progress message, screen the file, post a Completed message, and post any observation of unusual signals with a description to the data files discussion group on U Kentucky ASRG SETI .
Note: If you choose to do your SETI data screening on campus PCs, you
will probably need to load a new copy of your analysis programs every time
you change computers or every day, because the hard drives on campus public
PCs are automatically cleaned off daily. More information about GoldWave,
its data compressors/decompressors
(CODECs), and SETI can be found here.
If you run GoldWave and it does not recognize the file type you download,
you need to put the compressor ACM file
(right-click on this link and select Save As) into WINDOWS\SYSTEM directory
(Win95/98) or the same directory folder as your Goldwave.exe file (works
sometimes on Win95). You may also have to edit
your system.ini file. If so, under the label [drivers32] you'll find several
more acm file statements. Just add the statement:
msacm.msnaudio=Msnaudio.acm
Windows 98 users may also try downloading the latest version of Windows Media Player from Microsoft to solve the codec problem.
We are most interested in having students look for complex patterns that would not integrate over time into a stronger signal (the computers will detect these by themselves). An authentic extraterrestrial signal would exhibit a Doppler shift as the signal source moved toward and away from Earth as the planet rotates and translates relative to the deep-space source. Click here for an Excel spreadsheet to calculate the expected Doppler shift from rotation for any location on earth. For our telescope in its typical orientation, the expected Doppler shift is +/-6.07 Hz/min. This means that any real "signal" would be shifted by the rotation of the earth by 6.07 Hz per minute of recording. You can slow the screen frame rate in Goldwave to exaggerate the shift. Of course, the motion of the earth in orbit about the sun, as well as any rotation or orbital motion of a remote planet, would also cause a Doppler shift in the received signal. Theoretically, a Doppler shift would look something like this:
The angle of the tilt is a little exaggerated above. If you see any pattern that is not a line on the screen, note the running time and file name, capture an image of the screen, and post the information to the data files discussion group on U Kentucky ASRG SETI immediately. The ASRG has tools to examine the data more closely, and can move the radiotelescope to track the signal or establish its terrestrial location if it is an interference. The pattern you see will probably not be as pronounced as the one above. To prevent hoaxes and undesirable publicity, do not share the information with anyone else. Remember, the signal most likely arises from interference. If the signal passes all of the local tests for interference, other Project Argus radiotelescopes will be given the coordinates to try to confirm the signal.
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This signal was recorded on another program (FFTDSP, which scans vertically instead of horizontally), but the idea is the same. Real signals will not "wiggle" back and forth. Wiggling is characteristic of interference from nearby electronics. |
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This picture represents an occasional SETI problem. Any signal that seems to "curve" is probably caused by an airplane or a satellite orbiting Earth. The ASRG concentrates on frequencies around 1420 MHz, which is an internationally protected frequency. However, interferences can bleed over into this region occasionally. |
Click here to see examples of more interference signals.
The reporting methods are described in Where We Have Been Looking Lately.
Every time you download a file or complete analysis of a data file, please report your work by updating the post with a follow-up post. When you download a file, follow up with the file name and "In Progress". This helps to reduce unnecessary duplication of effort by others who may download the same file. However, please do not download a large number of files at one time unless you can analyze them in fairly short order. Our goal is to keep the time a file waits for analysis to a minimum to increase the chance of another station confirming any signal that might be detected.
If you find any unusual signals, post a report of file completion, and post the signal to the newsgroup or server. Report the time the signal occurred in the file (or by calling the lab) as soon as possible so confirmatory testing can begin, and include a screen capture image of the signal as a GIF or JPEG. Remember, in nearly 40 years of SETI, no signals from intelligent extra-terrestrial civilizations have been confirmed, so most suspicious signals turn out to be interference. We will share the results of our signal tests with you, and any credit that may be due based on the results of signal analyses and confirmatory testing by other Project Argus stations.
If you have any problems doing the data screening, please let us know and we can help. We appreciate your interest and time. Thank you, and good luck!
Return to the ASRG SETI page