50.2 MB (2.9 MB compressed)
4704 x 3729 pixels
39.9 x 31.5 cm ⏐ 15.7 x 12.4 in (300dpi)
LIBRARY OF CONGRESS / SCIENCE PHOTO LIBRARY LIBRARY OF CONGRESS / SCIENCE PHOTO LIBRARY
Communications antenna. This tropospheric scatter antenna and feeder horn (right) are part of the US Air Force's White Alice Communications System (WACS) built in Alaska during the Cold War. Tropospheric antennas use microwave radio signals and are able to transmit beyond the horizon using a method called tropospheric scattering. The signal is pointed in the direction of the receiver, just above the horizon. As the signal passes through the troposphere, some of the waves are refracted back towards Earth and picked up by the receiver. WACS was made obsolete by satellite communications. Photographed at Boswell Bay, Alaska, USA.
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