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Radio Astronomy and the Search for Extraterrestial Intelligence

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Radio Astronomy and the Search for Extraterrestial Intelligence new trends in communication technologies: radio astronomy and the search for extraterrestrial intelligence "Man's first step toward maturity may be to contact life beyond the solar system." -Bernard M. Oliver all, if hams were to be the first to communicate with extraterrestrials, it 1wouldn't be the first time a major scientific breakthrough had been made by hams - remember, not too long I ago hams discovered the ionosphere.' For several years I have been con- I templating the construction of a I system that would allow the reception r:, '-j.,i.."'"ru-,.. ?.,;I .,,I 4 :, I.:,:-, power times antenna gain) transmitter L * ... :,. 8 I .. located approximately 25 light-years away. I prepared this article in order to I a comprehensive overview of recent progress in radio astronomy (including fig. 1. This radio telescope - larger than three football fields - allows for the detection of thousands of radio sources extending to distances of 10 billion light-years (1 light- SETI) and to assess what Amateurs year = 6 x 10'2 miles). (Photo courtesy of Ohio State University Radio 0bsewatory.l can do with even limited resources. 'Unlike other events in science. the binh of radio astronomy can be traced precisely - to the early 15SB's If you're looking for a new of the state-of-the-art COmpOnentS when Carl B. Jamky. a Bell Telephone radio engineer, technical challenge, you may find found in a professionalradio astron- performed antenna noise studies for long-range com- munications at the wavelength of 14.6 meters. With SETI, the Search for Extraterrestrial In- with the possible excep- thew studies, Jamky proved that extraterrestrial radi- telligence, to be just the frontier you've tion of the very large antennas. tion can be received. Jansky's experiments were tol- been seeking. With today's microwave Because nobody knowswhat the first lowed, in the late 1930's, by Grote Reber. WSGFZ, an amateur astronomer who designed and built the finf technology, it is possible to communi- extraterrestrial signal will be like, there parabolic radiot elescv and perfom a of the cate anywhere within our galaxy. And is ample room for ham ingenuity. After galaxy at !he wavelength of 1.9 meten. although radio astronomy is still a relatively young science*, Amateur By Cornell Drentea, WB3JZ0, 7140 Colorado Avenue North, Radio operators have access to most Brooklyn Park, Minnesota 55429 10 March 1985 NOISE TUBE IFF AMP PHASE 1400-1750 MHz LAW DETECTOR ---a DETECTOR TO CONTINUUM rl ) CHART RECORDER 2 STAGE GaAs FET PREAMPS SWITCH - *- SWITCH TRANSISTOR 30 MHz 1420 MHz DRIVER RF AMP I-F AMP BPF POWER SPLITTER - v -n+> 1/ r I-F AMP 150 MHz BPF - A - A - 50 IDENTICAL CHANNELS TO 30MHz - n -9 : BPF 10.7 MHz COMPUTER -n rl 4 0 SQUARE LAW PHASE DETECTOR DETECTOR V w 120 MHz iw- -ilk COMPUTER CON TROLLED SYNTHESIZER 3rd LO 4 th LO 40 XX MHz 120 MHz fig. 1B. Block diagram of the Ohio State University radio telescope configured for SETI. The system covers an instantaneous bandwidth of 500 kHz through a bank of 50-channel IF filters at 10.7 MHz (individual filter bandwidth is 10 kHz). (Courtesy of Ohio State University Radio Observatory.) fig. 2. Master map of an Ohio University radiometer search. Maps below illustrate details of two sections indicated above. (Courtesy of Ohio State University Radio Observatory.) 12 March 1985 tegrator. The output transducer can take the form of a conventional chart +60 recorder or some other measuring de- t50 vice, or can be an analog-to-digital (AID)converter connected to a micro- f40 computer using a dot matrix printer for f30 the output. The format would be digi- . tized flux samples (values from OV to Z +PO 9V) at, for example, I-second intervals Pj $ +I0 printed out in 60-second columns for a total of 1 hour of information per 8 GO 2 0 T page. With such a receiver and a multi- ? ;-10 element beam antenna - and with D considerable skill and patience - a -20 serious Amateur can map the radio sky -30 in a short time. The methodologyemployed involves RIGHT ASCENSION (HRSI pointing the antenna at a known celes- (GALACrIC CENrERl tial location and then relying on the fig. 3. A map of the radio sky obtained with a simple amateur radiometer. Because of Earth's rotation to bring in the various the antenna's low resolution. discrete radio sources appear as a set of signal gradient natural radio sources. This requires lines resembling a surveyor's map. knowing celestial coordinates and times as well as converting the re- corded information and antenna posi- conventional radio allow for the detection of natural radio tion into the right ascension and de- astronomy sources located at great distances clination values in order to plot the There are two current trends in radio from Earth. A continuum survey of the signal onto a celestial map that would astronomy. The first, and by far most sky was made by the Ohio University resemble the actual sky (see fig. 3). popular, involves the study of wide- Radio Observatory, using the installa- A typical multi-element beam anten- band noise generated by powerful tion shown in fig. 1A and 1B. The na with a major lobe beamwidth bet- sources within our galaxy or in other receiver employed a liquid nitrogen- ween the half power points of approx- galaxies. The second, which occupies cooled parametric amplifier with a imately 30 degrees would allow a only a small fraction of the total activi- calculated system temperature of 95 natural radio source to pass through its ty, employs extremely narrow band- degrees K. The bandwidth was 8 MHz beam in approximately two hours (the width receivers designed for the detec- and the output was integrated over a apparent rate of movement of a celes- tion of intelligent monochromatic sig- 10-second period. Concurrent record- tial object is 15 degrees per hour at the nals in the microwave regions of the ing was performed after processing the equator). This in turn would be suffi- frequency spectrum where the level of data through IBM 7094 and 1620 com- cient to allow for the reception of intergalactic noise is lowest. puters. The entire system was syn- strong Milky Way sources such as Within the context of the first trend, chronized with a sidereal clock ac- Cygnus A, located approximately 500 it is relatively easy for an Amateur to curate to within 0.05 second. Results light-years away, and Cassiopeia A, build a radiometer receiver intended for have been plotted in maps of the located approximately 200 light-years casual observations of very strong region surveyed as shown in fig. 2. In away, regardless of the system's band- radio sources. Because of the uniform its search of almost the entire sky, width or operating frequency. distribution of wide-band noise over - from 36 to + 63 degrees, the Ohio very-long-baseline the receiver's bandwidth, no particular State project found 20,000 radio attention to local oscillator stability is sources. interferometry (VLBI) required. There would likewise be no While such performance cannot be In order to increase the resolution of need for precise tuning to compensate duplicated by the backyard radio as- a simple radiometer so that much for the Doppler shift in the incoming tronomer, remarkable results can be smaller or more distant objects can be signals caused by Earth's rotation and obtained with relatively modest installa- distinguished, increased antenna direc- by the relative motion between the tions. An Amateur radiometer is usual- tivity is required. This, in turn, dictates observed celestial object and our own ly a high-gain VHFIUHF superhetero- large physical installations, which are solar system. dyne receiver that features simple am- difficult and costly to build. To over- Professional radiometers employ plitude modulation detection followed come this problem, a new kind of a re- giant steerable antenna arrays that by a DC amplifier equipped with an in- ceiving system, the interferometer, March 1985 13 ANTENNA DEVELOPMENT & MAMlJFACTURlNG INC. Conlacl Antenna Dmmlopmenl & Manufacturing 314.6' your neanr .. .- Echosphere Corporation Heilner Communicatio National Satellite 2250 South Rar~tanBldg. A 1805 Burlington 10779 Satellite Blvd. Englewood. CO 80110 Columbia. MO 65202 Orlando, FL 32809 303-935-1909 31 4-474-6414 305-851-4738 Echosphere East Hoosier Electronics Avcom of Virginia. Inc. 10536 Lexington C P.O. Box 3300 500 Southlake Blvd. Knoxville. TN 379: Twre Haute. IN 47802 Richmond. VA 23236 615-966-4114 812-238-1456 804-794-2500 Echosphere West Nat'l Satell~teCommu Video Specialties. Inc. 5671 Warehouse V 21st Century Park 417 Chambers Drive Sacramento, CA 9 Clifton Park. NY 1206 Boonev~lle,MS 38829 916-381-5084 518-383-221 1 601-728-7700 was developed. This system uses a telescopes thousands of miles apart, Germany, astronomers have recently pair of antennas and transmission lines with local oscillators and subsequent- made some exciting new discoveries. separated by a specific horizontal dis- ly recorded data synchronized within The first quasar (3C 147) ever observed tance (i.e., the "baseline") extended a fraction of a microsecond through with this method has been effectively to an even multiple of the operating the use of atomic clocks. This elimin- mapped; it is located some seven wavelength, preferably more than fif- ates the need for running coaxial billion light-years away. The resolution teen wavelengths. The system is usual- cables from the antenna sites to the was in the order of 0.01 arc-second - ly configured in an east-west orienta- central location for processing, and the a considerable improvement over the tion.
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