Harvard-Arecibo off-line SETI
Harvard-Arecibo off-line SETI was a SETI project conducted by Harvard researchers in 1978, using the Arecibo radio telescope, which targeted 200 candidate stars. The search was centered on the 21-centimeter line of neutral hydrogen and examined 1 kHz instantaneous bandwidth segments with a resolution bandwidth of 0.015 Hz (the highest resolution and sensitivity ever achieved in SETI). The tiny bandwidth of 1 kHz meant that a transmitting civilization would have had to precompensate the carrier beacon for their motion relative to the Sun – an unlikely but not unfeasible scenario.1 Analysis of the data took place off-line by long Fourier transforms. A follow-up search at Arecibo was carried out by the Harvard group in 1982 using "Suitcase SETI".
1. Horowitz, P. "A Search for Ultra-Narrowband Signals of Extraterrestrial Origin," Science, 201, 733 (1978).