Project Sentinel was a dedicated all-sky search conducted from 1983 to 1985 using the Harvard-Smithsonian radio telescope and a reconfigured version of "Suitcase SETI".1 Covering the northern sky in drift-scan mode around the frequency of the 21-centimeter line, this was the first dedicated high-resolution SETI program. An all-sky search was chosen, unlike the earlier Harvard-Arecibo off-line search which was a targeted search, because the larger beam size (30 arcminutes at Harvard, compared with 3 arcminutes at Arecibo) enabled a full sky search in about 200 days. Like its predecessors, Sentinel achieved high resolution at the expense of total frequency coverage (2 kHz instantaneous bandwidth for Sentinel and "Suitcase SETI," 1kHz for the off-line search), requiring that a transmitting civilization target the Sun specifically, in order to adjust the frequency of its signals to take account of the relative motion of the local and heliocentric frames. Moreover, the long integration time, of about 30 seconds, prevented immediate reobservations of interesting candidate signals. These problems were addressed in a subsequent Harvard search known as Project META.
1. Horowitz, P., Matthews, B. S., Forster, J., Linscott, I., Teague, C., Chen, K., and Backus, P. "Ultranarrowband Searches for Extraterrestrial Intelligence with Dedicated Signal-Processing Hardware," Icarus, 67, 525 (1986).