A modest all-sky search for narrowband radio radiation near the 21-cm hydrogen line

Since 1973 an all-sky, full-time search for narrowband radio radiation (presumably of intelligent origin) near 21 cm has been underway at the Ohio State University Radio Observatory. The search concentrates on a band 380 kHz wide centered on the hydrogen line, corrected to the Galactic Standard of Rest. The search is limited by lack of funding and personnel. It has been found that beam switching is an important technique for reducing terrestrial interference, and that galactic hydrogen emission does not cause significant extraterrestrial interference. A number of small-diameter cold hydrogen clouds have been discovered. No confirmed narrowband extraterrestrial signals have been found between +48° and +14° in declination above the detection limit of 1.5 × 10^?21 W/m².