The SERENDIP program is an ongoing search for narrow band radio signals from extraterrestrial civilizations. Each generation SERENDIP instrument has on average been about 35 times more powerful than its predecessor. In this paper we discuss the hardware design of the latest generation instrument, SERENDIP IV, which will be deployed in early 1997 for a 21 cm sky survey at the National Astronomy and Ionospheric Center’s 305 meter radio telescope in Arecibo, Puerto Rico. SERENDIP IV is a 167 million channel spectrum analyzer, covering a 100 Mhz bandwidth, with 0.6 Hz resolution and a 1.7 second integration time. SERENDIP IV’s modular design incorporates a bank of digital mixers and filters to separate the 100 MHz band into forty 2.5 MHz sub-bands. Each 2.5 MHz sub-band is further broken down into 0.6 Hz bins by means of a four million point fast Fourier transform. The resulting power spectra are analyzed by 40 high speed processors. Narrow band signals having power significantly above background noise levels are recorded along with telescope coordinates, time, and frequency. The data are sent in real time to Berkeley for analysis. SERENDIP IV hardware is also utilized by the Ohio State University SETI program and pulsar programs at Nancay Observatory (France), the US Naval Research Lab, the Effelsberg telescope (Germany), NRAO’s Greenbank Observatory and NAIC’s Arecibo Observatory.
The Berkeley SETI effort has been ongoing for more than twenty years. During this period we have carried out extensive SETI searches, but of at least equal importance, we have been on the forefront of instrumentation development, the development of interference rejection and detection algorithms, and educational efforts. Our instrumentation has evolved from a 100 channel spectrometer (SERENDIP I) to our latest machine (SERENDIP IV) with 168 million channels. In addition to supporting our SETI work, our hardware has been used by NASA for RFI surveys and to check the Mars Survey relay transmitter. Our designs have influenced several of the major SETI hardware systems, and a SERENDIP III system is currently being used in the Ohio State SETI group. Our hardware has also been incorporated in pulsar instrumentation at NAIC (Arecibo), NRAO (Greenbank) and Bonn, Germany. We have just completed a 4 year search at the world’s largest radio telescope at Arecibo. We covered 93% of the observable sky at least once, and 44% of the sky at least 5 times, with a sensitivity of ~ 3 × l0−25Wm−2. We collected and analyzed information from over 1014spectral bins and logged and analyzed over 2 × 108signals of potential special interest. We have developed extensive analysis programs to identify and remove interference and to search for signal characteristics which are expected from an extraterrestrial signal. Our algorithms were successful in removing all but 0.01% of spurious RFI in the Arecibo data set. We have involved over 30 undergraduate and graduate students in our effort, and 5 Master's theses have been awarded for work on the SERENDIP project. Our next effort will use our SERENDIP IV hardware at Arecibo Observatory to carry out a 21 cm survey of the Arecibo sky.
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