In late October 2009, I heard a most unusual commercial on a local AM station. Television users were asked to rescan for channels on their over-the-air sets. A url was provided for more information: www.sutrotower.com.
Those who live in or near San Francisco are likely familiar with the name Sutro Tower. This ominous, three-pronged antenna dominates the skyline near the center of the city. San Francisco's hilly terrain made line-of-sight propagation difficult for analog television and FM stations, prompting the construction of Sutro Tower from 1971 to 1973.
A new graphic on sutrotower.com shows the location, callsign, and frequency/channel of each station with an active or inactive antenna on the tower. The website also hosts an RF exposure report showing the findings of a firm called Hammett & Edison.