Stratovision was an airborne television transmission relay system using aircraft flying at high altitudes. In 1945 the Glenn L. Martin Company and Westinghouse Electric Corporation originally proposed television coverage of small towns and rural areas, as well as the large metropolitan centers, by fourteen aircraft that would provide coverage for approximately 78% of the people in the United States. Although this was never implemented, the system has been used for domestic broadcasting in the United States, and by the U.S. military in South Vietnam and other countries. Technology Because the broadcasting antenna for Stratovision is usually hung beneath the aircraft in flight, it naturally has a great command of line-of-sight propagation. Although transmission distances are dependent upon atmospheric conditions, a transmitting antenna above the Earth's surface has a line of sight distance of approximately . A Stratovision 25 kW transmitter operating from at 600 MHz will achieve a field intensity of 2 millivolts per meter for a high receiving antenna up to away from the aircraft. Early tests Stratovision tests were undertaken between June 1948 to February 1949. The first phase was undertaken by the Glenn L. Martin Co. and Westinghouse using a twin-engine PV-2 aircraft flying at that transmitted with 250 watts on 107.5 MHz and 5 kW on 514 MHz at Baltimore, Maryland so that recordings could be made at various locations ranging from Norfolk, Virginia to Pittsburgh, Pennsylvania and Boston, Massachusetts. The second phase of testing was undertaken by these companies using a stripped-down B-29 Superfortress flying at . The plane was equipped to receive a relay transmission from WMAR-TV in Baltimore, which was then relayed over a 5 kW video transmitter and a 1 kW audio transmitter for reception on 82-88 MHz with a television set tuned to Channel 6. The aircraft received its originating signals from circular dipoles attached to a streamlined eight-foot (2.5 m) mast atop of the aircraft's vertical tail fin. The retractable long broadcasting antenna hung vertically beneath the aircraft. It was composed of a two-element turnstile array for video and a single-element circular dipole for sound transmissions. The receivers, transmitters and necessary air-conditioning were all powered by the plane's engines using three 15 kVA, 500 Hz alternators. Without air conditioning the transmitters in the interior of the aircraft would have generated a temperature of 134 degrees Fahrenheit (57 degrees Celsius) with an outside air temperature of 25 degrees Fahrenheit (minus 4