The largest single radio telescope is the 305-meter (1,000-foot) diameter Arecibo Telescope, located in Puerto Rico. The reflecting dish, made of 40,000 perforated aluminum panels, is located in a mountain valley. The actual antennas are in a 900-ton platform, suspended on cables 137 meters (450 feet) above the dish. The antennas, sensitive to frequencies from 50 MHz to 10GHz, detect signals collected by and reflected from the dish, and can be moved to determine the direction from which the signals are coming. Arecibo also performs radar astronomy using a 1 megawatt radar transmitter to send signals to the other planets. The telescope then detects the faint echos.
Highly sensitive telescope arrays like this one are used by radio astronomers to detect signals created by atoms, molecules, and ions from space.