American television directory (1946)

WINGS TO TELEVISION Westinghouse official predicts unprecedented coverage with less power required, lower installation and oper¬ ation costs and many services flown simultaneously. By G. E. NOBLES Westinghouse Radar Expert and Originator of “Stratovision” T wo methods are being used to dis¬ tribute television programs, namely co¬ axial cables and radio relay stations. Coaxial cables have been installed and used to distribute television programs. Published information indicates that by approximately 1950 it is intended to complete a cross-country link from Boston to San Francisco and make it available for the distribution of tele¬ vision programs to television broadcast¬ ers. The construction cost alone for laying this cable is in the order of several dollars per foot. Therefore, the proposed route will cost many millions. Relay Chain Requires 100 Towers The other approach to the program distribution problem is a series of radio relay stations which use highly direc¬ tional radio for relaying the program from one point to another. A typical in¬ stallation in a relay-link chain consists of a tower approximately 300 feet high with a receiver to receive the programs from one tower and a transmitter to relay the program to the next succes¬ sive tower in the chain. Because of the line-of-sight characteristics of the fre¬ quencies involved in this relaying, re¬ lay towers will be located approximate¬ ly 35 miles apart. This means that 100 relay towers would be required to get a program tie-up from New York to Hollywood. A system of relay stations is now connecting Washington, Phila¬ delphia, New York and Schenectady and plans have been published for a chain of relay stations which will net¬ work the country. Either of these systems — coaxial or radio relays — has the disadvantage that large quantities of expensive equipment are necessary to distribute the program. Imagine the amount of cable or relay¬ ing which will be required before these 400 stations can be tied together in a television network based on data sub¬ mitted to the Federal Communications Commission by the Radio Technical Planning Board. The operation of relay or cable net¬ works presents very sizeable technical problems because of the number of times the program must be handled. At each relay station additional distor¬ tions are added to the signal in the form of noise, phase distortion, and amplitude distortion. If a television transmitter were placed in an airplane and the television program broadcast from the airplane in flight, the transmitter’s coverage area would be increased by virtue of an increased line-of-sight distance to the horizon. At an altitude of 2,000 feet, a coverage radius of 50 miles is possible, whereas at an altitude of 30,000 feet a coverage radius of 211 miles is possible, and at 50,000 feet about 300 miles is possible. Another very interesting feature of high-altitude operation is the fact that as the station’s height is increased, the transmitted power necessary to deliver a usable signal to the line-of-sight dis¬ tance is sharply reduced. Fifty kilowatts of power will deliver a usable signal at approximately 50 miles from a ground station, whereas only one kilowatt of power will deliver the same usable signal at approximate¬ ly 200 miles from 30,000 feet. Smaller powers are required from the higher altitudes because the path difference between the direct wave and the ground-reflected wave is increased. The fact that such small powers are required from high altitudes is very inviting for several reasons : 1 — The broadcast service area cov¬ ered is relatively tremendous. 2 — The smaller-powered transmitters can be made in sizes and weights which are practical for carrying in an airplane. 3 — Powers of the order of one kilo¬ watt can be generated with tubes which are available today — even for the CBS high-definition color television frequencies. 4 — The small amount of power re¬ quired to operate the transmitter can be obtained from power plants installed in the airplane. If so desired, the power required to operate the equipment could be taken for generators con¬ nected to the aircraft’s engines. This power will represent only about 4 per cent additional load on the plane’s engines. A Network of Airplanes Let us now look at the program dis¬ tribution problem involved if we use radio relaying between a network of airplanes at 30,000 feet. If we transmit from one plane to the next plane in the chain, the line-of-sight distance be¬ tween the two planes is about 400 miles instead of the 35-mile spacing for ground stations. With such large relay spacings a program link from SIX MILES UP, 14 planes carrying transmitters can beam television programs to 78% of the population. Circles 422 miles in diameter represent 103,000 square miles each plane covers. 29