[Big Ear Masthead]

SETI in the 1970s

By Bob Dixon.
Compiled from papers by the following individuals: Bob Dixon, Jerry Ehman, Russ Childers, Marc Abel
Additions By Herb Johnson

The Search Begins

The Ohio SETI (Search for ExtraTerrestrial Intelligence) Program began with a strong impetus from NASA's Project Cyclops. The goal of Cyclops - a paper study conducted in the early 1970s - was to assess what it would take in terms of time, people, equipment, and money to mount a large search for radio signals from interstellar civilizations. The end result was a report which was widely circulated as a NASA Special Publication, recommending a small array of radio telescopes which would grow with time as needed.

During my Project Cyclops research, it became clear to me that many theoretical papers were being written about SETI but no one was doing any extensive actual searching. I also realized that we had a large, fully operational radio telescope available at Ohio State University (OSU), affectionately known as "Big Ear", which was designed explicitly to search for new radio signals in the sky. It had just completed the largest all-sky survey of natural radio signals made up to that time, the "Ohio Survey". Coincidentally, this telescope was also chosen by the Russian scientist Gindilis as the telescope most suited for SETI, due to its unique surveying ability.

Although we had no money, we did have a crew of able volunteers on hand. Faced with the alternative of ultimately turning off the telescope and letting it rust away, we decided that we had a responsibility to seize the opportunity which had been thrust upon us and start a real SETI program. It did not take too much arguing to convince Dr. John Kraus, Director of the OSU Radio Observatory, to allow me to use the telescope for humanity's first full-time SETI program.

Preliminary Search: 1973 - 1975

We went on the air in 1973, using an eight-channel receiver system, originally constructed for twenty-one-centimeter (21-cm) hydrogen line observations by Bill Brundage. Bill later went on to become Chief Engineer of the ninety-meter (three hundred foot) radio telescope at Green Bank (NRAO). Later still he was responsible for preparing the Very Large Array (VLA) in New Mexico to receive the faint VOYAGER 2 spacecraft signals during its flyby mission of the planet Neptune in August of 1989.

The bandwidths of the channels ranged from ten to fifty kilohertz (kHz), depending on their distance from the center frequency. The output of the eight channels was plotted as wiggly lines on pen recorders. The charts were laboriously searched for unusual signals by graduate student Dennis Cole - now a contractor to the Jet Propulsion Laboratory (JPL) - and used as the subject for his master's thesis in Electrical Engineering. This may have been the first graduate degree ever awarded in SETI.

Galactic Center of Rest

The search strategy chosen at the time was to explore in the vicinity of the 21-cm hydrogen line, Doppler correlated to the Galactic Standard of Rest. Due to the random motions of the stars and the rotation of our Milky Way galaxy, signals transmitted at the hydrogen line frequency (1420.4056 megahertz, or MHz) would be received at somewhat different frequencies because of the Doppler shift. To avoid this frequency ambiguity, we made the deliberate assumption that any civilization transmitting at the hydrogen line would offset their transmission frequency in just the right way to remove all their motions with respect to the center of the galaxy, which is the only unique reference point shared by all the galactic inhabitants.

It was then up to us to offset our receiver frequency to compensate for Earth's motions to arrive at this unique "galactic" frequency. Because of humankind's uncertainty about the galactic rotation velocity (measured by observing the motions of the stars and gas in our stellar neighborhood), we still had to search a total bandwidth of several hundred kHz. A lot of chart paper was generated during the two years this effort continued, but no recognized signals of intelligent origin were found.

The Search Program of 1975-1985 and the IBM 1130

By 1975, a fifty-channel filter bank receiver had been borrowed from Green Bank. Software for the already old IBM 1130 computer had been developed by Professor Jerry Ehman - then Chairman of the Division of Management Science at Franklin University - and me, to process all fifty channels continuously. The software was sophisticated, with many internal checks for false alarms and equipment malfunctions. Each of the fifty channels was processed independently, and the computer automatically removed the individual gain and baseline variations of each channel.

A number of search algorithms were run simultaneously, including searches for both isolated pulses and continuous signals which rose and fell in intensity in just the predicted way (for a continuous, narrowband signal) as they passed through the antenna beams. The highly processed output data were printed every twelve seconds for all fifty channels. Signals the computer thought were "interesting" were also flagged and saved on punched cards for later analysis.

The IBM computer was built like a battleship and ran without fail for many years. Its operating system could run huge programs in a tiny memory very efficiently. It was fast for its time.

Over the years, a few cold hydrogen clouds were found and huge piles of computer printouts accumulated. There was no magnetic tape drive or equivalent device available, so there was no way to record all the data permanently in computer-readable form. Only the small fraction of data represented by the "interesting" signals were preserved in computer-readable form. Along the way, a small NASA grant was received, which continued until the mid-1990's.

1977 and WOW!

[The Wow! Signal]
Click here for explanation of the code.

Two types of unexplained signals were detected during this search. The first kind is quite rare, with the best example being the "Wow!" signal found in 1977. This name was unintentionally applied from Jerry Ehman's comments ("Wow!") in the margin of the computer printout when he noticed the signal. The signal was unmistakably strong and had all the characteristics of an extraterrestrial signal. It was narrowband and matched the antenna pattern exactly, indicating it had to be at least at lunar distance. A signal from a nearer object would show a wider pattern.

However, the strange signal was not coming from the direction of the Moon or any planet, or even any particular known star or galaxy. Of course there are always many distant stars and galaxies in the beam of a radio telescope all the time, but that is not significant. A check of artificial satellite data showed that no publicly-known Earth satellites were anywhere near the position of the signal source. Furthermore, the frequency of the signal was near the 1420 MHz hydrogen line, where all radio transmissions are prohibited everywhere on and off Earth by international agreement. We searched in the direction of the "Wow!" signal hundreds of times after its discovery and over a very wide frequency range.

We never found the signal again. It was gone. In fact, while we were receiving this signal the first time, it turned off as we listened. The radio telescope actually receives two beams from the sky at once (somewhat offset in direction from each other) and subtracts one from the other to cancel out terrestrial radio interference. Objects in the sky are usually received twice with a slight delay, once in each beam. But the "Wow!" signal was received only once, indicating either that it turned off after the first beam received it, or that it turned on after the first beam had passed it. A number of organizations and individuals have searched this area of sky for a repeat of this signal: no subsequent detections were found.

What was the "Wow!" signal? Probably we will never know. Conceivably it could have been a secret military satellite in solar orbit, transmitting on an illegal frequency. Military transmitters often ignore civilian agreements. Its characteristics rule out any terrestrial transmitter, near-Earth satellite, reflection from space debris, or equipment malfunction. Perhaps it was a transmission from some other civilization. If so, it seems that they were not trying very hard to attract our attention, since the signal disappeared before we could really find out what it was.

The 1977-1983 Survey and Unexplained Events

The other kind of unexplained signals we receive are much more numerous. These are narrowband pulses (lasting less than ten seconds) which go "bump in the night". There have been thousands of such signals received, apparently from all over the sky, and never from exactly the same direction more than once.

These signals were detected by our automated "search strategies"; methods that looked for a SINGLE isolated channel of activity for various short periods of time. Since our shortest period of "sampling" signals is about ten seconds, and the longest period is the time a stationary source remains in the beam (or view) of the telescope (approximately 70 to 150 seconds depending on declination), our strategies reflected these limits. We found over 30,000 "detections" of one-channel events; only 1124 were "well above" the average noise level. These events divided up as follows:

For one sampling period only (Search Strategy 1 (SS1), 10 sec):

  • 62 events at 20 standard deviations or higher
  • 251 events at 10 standard deviations or higher (exclusive)
  • 734 events at 6 standard deviations or higher (exclusive)

For two sampling periods (SS2, 20 seconds): 228 events

For three sampling periods (SS3, 30 seconds): 60 events

For the full view of the telescope: 100 events at five standard deviations or higher.

Clearly these signals are not from any single source (intelligent or otherwise), but they are very interesting in their own right. They could be some form of previously unknown astrophysical phenomenon. As an example, pulsars were first thought to be of alien origin when discovered in 1967, due to their regularly timed radio waves. They are now known to be rapidly rotating neutron stars, the remains of supernovae.

Of course pulsed signals like these could easily be caused by terrestrial radio interference or equipment malfunction. But if those were their sources, then they should appear randomly scattered across the sky. The interesting thing is that they do not. They exhibit a zone of avoidance along the galactic plane and areas of concentration above and below the galactic center, along the galactic north and south polar axes.

It is possible that the zones of avoidance and concentration are caused in some complex unknown way by an interaction between the galactic continuum radiation and the automatic gain and baseline correction algorithms in the computer. We simply do not know. A resurvey of a portion of the same area shows roughly the same effect, so the phenomenon appears to be repeatable. We hoped at the time to conduct another survey with new equipment, to see if this effect will continue over time. This became the LOBES survey over ten years later.

This SETI survey continued in the 50-channel form until 1983. No Wow!-like events re-occurred. So, after our reports, the data was archived for future research: about 5.5 million records of 50 data channels, sampled and printed every ten seconds; and miles of analog paper strip charts, produced over the seven year life of our program of daily observations.

Big Ear Declinations 1977-1984
By Russ Childers
Data From Punched Cards
All times EST, declination = observed = (theodolite - 1 degree)

Data: Year - Month - Day - Degrees(+/-) - Minutes

View Data In Printable Format



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Last modified: August 13, 2005