Online Encyclopedia
Stratovision
Stratovision is a airborne television transmission relay system from aircraft flying at high altitudes. In 1945 the Glenn L. Martin Co. and Westinghouse Electric Corporation advocated 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 U.S.A. This system has been used for domestic broadcasting in the USA; used by the US military in Vietnam and other countries and attempted by pirate radio operators but not successfully employed.
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Technology
Because the broadcasting antenna for Stratovision is usually hung beneath the aircraft in flight, it naturally has a great command of a line of sight. Although transmission distances are dependent upon atmospheric conditions, a transmitting antenna 30,000 feet above the earth’s surface has a line of sight distance of approximately 211 miles.
A Stratovision 25kW transmitter operating from 30,000 feet at 600 megacycles will achieve a field intensity of 2 millivolts per meter for a 30-foot high receiving antenna up to 238 miles away from the aircraft. However, the the height of the receiving antenna height has to be reduced according to the distance that the receiver is to the flight path of the transmitter.
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 Electric Corporation using a twin-engine PV-2 aircraft flying at 25,000 feet that transmitted with 250 watts on 107.5 mc and 5kW on 514 mc 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 30,000 feet. The plane was equiped to receive a relay transmission from WMAR-TV, the Westinghouse television studios in Baltimore, which was then relayed over a 5kW video transmitter and a 1kW audio transmitter for reception on 82-88 mc with a television set tuned to Channel 6.
The aircraft received its originating signals from circular dipoles attached to a streamlined eight-foot mast on top of the aircraft's vertical tail fin. The retractable 28 feet 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-cycle alternators. Without air conditioning the transmitters in the interior of the aircraft would have generated a temperature of 134 degrees Fahrenheit with an outside air temperature of 25 degrees Fahrenheit.
The tests were watched by many television viewers who sent in reception reports. From these reports it was calculated that Stratovision would require only eight relay planes to provide a transcontinental network and six additional planes to provide coverage to 78 percent of the United States. Mr. C. E. Nobles who was the head of Stratovision for Westinghouse said in his report:
- " The major technical problems of the system have been solved, and the commercial development awaits only the crystallization of public demand for the expanded services offered by airborne broadcasting, application of the system by the radio industry to meet this demand, and the clarification of channel facilities available to make possible this application."
Education by Stratovision
In 1961 a joint project by Indiana University and Purdue University commenced a Stratovision service from the airfield of Purdue University. The service was called Midwest Program on Airborne Television Instruction (MPATI), which transmitted educational television programs four days a week from a DC-6 (however, this could have been a DC-7) aircraft flying at 20,000 feet over north central Indiana.
MPATI delivered its programs to television channels 72 and 76 in the UHF band, by transmitting videotaped lectures from the aircaft to an estimated potential 5,000,000 students in 13,000 schools and colleges. The aircraft were equipped with two, two inch videotape machines and two UHF transmitters.
When MPATI signed on it used a "Indian head" test pattern card which was shown for five minutes before and between programs. The service ended in 1968 when it became embroiled in legal action over their application of Stratovision in a controversy with the Westinghouse company.
Propaganda by Stratovision
During the war in Vietnam, the United States Army also used Stratovision television technology when it flew Operation Blue Eagle from 1966 to 1972 over the Saigon area of South Vietnam. The television programs were aimed at two audiences on two channels. One was aimed at the general public and the other was intended for the information and entertainment of US troops who were stationed in South Vietnam.
Broadcasting planes using technology based upon the Stratovision concept, have since been used in most of the areas of world conflict where the United States military has been a party. This includes Bosnia and Iraq.
Pirate television by Stratovision
In 1969 news stories began to appear in the United Kingdom that Ronan O'Rahilly, the founder of the pirate radio ship based service called Radio Caroline, which at that time was not on the air, was about to launch Caroline Television instead. His plans called for two aircraft, one in service and one as a relief, which would transmit commercial television programs to Britain by Stratovision. Although these stories continued for some time nothing became of the project.
There have been other rumored attempts but they also failed to transpire.
Stratovision: a temporary service
Today the Stratovision concept is used as a stop-gap measure where land based transmitters are not possible and where large areas of territory need to be served with a television program. Due to the advent of fibre optic cable systems and direct broadcast satellite services, the need for Stratovision as a permanent means of television delivery has become unnecessary.