Wednesday, January 11, 2012

1955: Radio And Radar


1955: Radio And Radar

Archives consist of articles that originally appeared in Collier's Year Book (for events of 1997 and earlier) or as monthly updates in Encarta Yearbook (for events of 1998 and later). Because they were published shortly after events occurred, they reflect the information available at that time. Cross references refer to Archive articles of the same year.
1955: Radio And Radar
Tropospheric Scatter System.
The Lincoln Laboratory at South Dartmouth, Mass., has devised a radio signal system that makes continental defense against air attack possible. The new transmission system does so by making radio communication 99.9 per cent reliable, in contrast to conventional short-wave transmission which is 70 to 80 per cent efficient. With it, the signal barrier that blankets the Arctic in radio blackouts for months at a time has been broken.
Short-wave transmission from the Arctic in the four winter months is almost impossible because of atmospheric conditions. Even if radar observers in the Arctic were to spot a flight of planes during these months, it would be highly unlikely that a warning message would be received in the United States. Thus, continental defense always has been vulnerable in the winter. This threat was ended by the new system which works efficiently at any season. William H. Radford and Jerome B. Wiesner supervised development of the technique at Lincoln Laboratory.
How It Works.
Described as a 'tropospheric scatter system,' the technique is so new that even Lincoln Laboratory scientists do not understand exactly how it works. The system uses an ultra high-frequency (UHF) transmitter to send out signals. As a result, a straight, unbending beam, much like the frequency-modulated (FM) or television beam, is transmitted. This differs from the amplitude-modulated (AM) beam of commercial radio stations, which is called a ground wave and follows the earth's curvature. The signal sent out by the new technique also varies from shortwave which bounces back and forth between the earth and atmosphere as it travels around the world. The beam of the new system is not exactly the same as an FM or television beam which is sent out on a 'line-of-sight' level; UHF signals are beamed slightly upward. The tilt prevents them from being blocked by hills or other obstructions that blackout TV and other line-of-sight beams.
Dr. Radford, explaining the new system, compared powerful UHF beams to a searchlight aimed at the sky. 'Even a searchlight behind a hill can be seen for great distances,' he said, 'because dust and moisture particles in the air deflect some of the rays making the streak of light visible from the side. We believe that something similar happens in scatter transmission. Upper air layers deflect some of the radio beam making it possible for a station over the horizon to receive the message. The signal received by an over-the-horizon station has less than one-millionth of the power with which it was transmitted.'
Defense Use.
The system already is in service between the U.S. Air Force base in Thule, Greenland, and Loring Air Force base in Maine. In addition, it will be used to connect the Distant Early Warning line now under construction in the Arctic with the U.S. Air Force defense command.
The Texas Tower which was towed from Boston in July 1955 to its ocean base on Georges Bank carries equipment for the system. A six antennae station has been erected in South Truro, Mass., to serve as the radio link between the Texas Tower and Lincoln Laboratory headquarters in Lexington, Mass. It will pick up signals from the tower 116 miles off Truro and beam them 66 miles to Lexington.
Commercial Use.
Round Hill, the most powerful station in the Lincoln Laboratory network which extends from Massachusetts to Iowa and Texas, has demonstrated possible commercial applications of the system. The station has picked up and relayed a network television show direct from Red Bank, N.J., a jump of 188 mi. This may be contrasted to the line-of-sight transmission systems presently used in television. The transmitters now employed are limited to a range of only about 30 mi. For this reason, commercial television networks must use seven relay points between New York and Boston.
TACAN.
International Telephone and Telegraph Corp. announced a new and revolutionary radio navigation system. Known as TACAN (tactical air navigation), it is expected to have a far-reaching effect on the nation's navigation and air-control program. It was developed for the U.S. Navy because of the lack of an accurate radio navigation aid capable of operating on board aircraft carriers and in military theaters where time-consuming installations and the selection of favorable sites is not possible. TACAN has been accepted by the U.S. Air Force for interservice standardization and is being advanced by the Air Navigation Development Board (ANDB) as the basis for a common navigation system capable of serving all types of aircraft.
Operation.
While TACAN is still a classified military system, the performance characteristics of the equipment have been declassified. The system provides an aircraft pilot with continuous information on the position of his craft relative to the distance and direction of flight from a fixed ground station. The information is given instantly, automatically, and with extreme accuracy. The equipment is small and compact, occupying only about 1,000 cu. in. of space. This is several times less than that occupied by other airborne units which provide less navigational information.
Tests have shown that TACAN has an azimuth, or bearing, accuracy to within one degree. This is probably the highest ever achieved by a bearing-giving system and may be attributed to improved design features and the relative absence of site effects. Besides such high azimuth accuracy, TACAN has a distance accuracy of the order of 0.2 mile. Thus, it is superior to ordinary radar accuracy.
Advantages.
TACAN differs from other aids in that it is an integrated navigation system rather than a conglomeration of separate, unrelated navigational aids as have been available to aviation in the past. Its unique features include: the reduction of the frequency spectrum used to the minimum band width for the accuracy demanded; large savings in the volume and weight of airborne equipment by combining azimuth and distance functions into the same radio-frequency channels and circuits; a corresponding reduction in the number of radio-frequency antennas and cables. In addition TACAN permits the maximum accuracy in direction and distance indications which is so important to safety in the navigation of aircraft operating from ships, mobile units, and certain ground sites. This is in contrast to former systems which have been limited in performance because of damaging effects of surrounding physical characteristics, such as hills, masts, and buildings.
Microwave Horn-Reflector Antenna.
A new type of microwave antenna, designated the 'horn-reflector,' was recently installed by the long-lines department of the American Telephone and Telegraph Co. at a station near Terrel, Tex. It consists of a feed horn, an expanding horn-shaped casing, and a section of a parabolic reflector facing the mouth of the horn. The aperture of the horn has a cross section of 65 sq. ft. Energy from the radio equipment is transmitted through a circular wave guide to the feed-horn which has a smooth transition from the 2.8-in. inside diameter of the wave guide to the 11.6-in. aperture of the feed-horn. In transmitting, the radio waves leave the wave guide, expand in the feed-horn and lower portions of the antenna, and are then reflected in parallel lines from the surface of the parabolic reflector. In receiving, the operation of the antenna is reversed. The incoming waves arrive in parallel lines and are reflected by the section of the parabola to the focal point in the feed-horn and then through the wave guide to the radio equipment.
The horn reflector replaced the 'delay-lens' antenna which is used on most Bell System radio relay routes. It operates over a very broad frequency band. One of the new antenna will be able to handle simultaneous transmission in the common carrier band of 3,700-4,200 mc (megacycles) and also in bands in the region of 6,000-11,000 mc. The gain in this type of antenna over its predecessor is from about 39 to 48 decibels at 11,000 mc. Eventually it will be able to handle 15,000 telephone conversations and 10 television programs at the same time. The horn reflector is capable of transmitting simultaneously both horizontally and vertically polarized waves. This feature will be used to reduce cross talk between adjacent channels.
The installation near Terrel, Tex., is the first commercial use of the horn reflector. Others will be in use for telephone and television service on a route now under construction between Dallas, Tex., and Jackson, Miss.
Long-Distance Waveguide.
The Bell Telephone Laboratories announced a method of transmitting telephone conversations and television programs over long distances. The new medium is a long-distance waveguide which uses hollow metallic tubes roughly two in. in diameter.
Waveguides of metal tubing have been used for some time for short-distance transmission. It would be possible to use them for long distances if such tubes were perfectly straight. This, however, is impracticable. The new long-distance waveguide is constructed of thin copper wire tightly coiled, like a spring under pressure, inside a flexible outer coating which holds the coiled wire in place. It need not be straight and can actually carry signals around corners. Experiments indicate that both the solid-tube waveguide and the new coiled-wire or 'helical' waveguide can be used together in communication systems.
The helical waveguide is still in the experimental stage. During a test, engineers bounced signals back and forth in a copper tube 500 ft. long, for a distance of 40 miles. They calculated that the same waves would have traveled only 12 miles in a coaxial cable before undergoing a corresponding loss in strength. The new system operates in a frequency range so high that it has never been put to use for communications. The super-high frequency established by the Federal Communications Commission goes up to 30,000 mc; the carrier frequency for the new waveguide is about 50,000 mc. The higher the frequency in the waveguide, the less the loss through attenuation. This behavior is exactly the reverse of that of other forms of transmission.
Bell scientists believe that the helical waveguide may some day simultaneously carry cross-country tens of thousands of telephone conversations and hundreds of television programs. The top capacity for the most modern coaxial cable system is 1,860 two-way telephone conversations or 600 such telephone conversations and two television programs on a pair of coaxial tubes.
Transistor Radio.
A pocket radio set which uses transistors instead of tubes is being manufactured by Regency, a division of Industrial Development Engineering Associates, Inc. The diminutive radio measures 3” by 5” by 1½” and weighs less than 12 oz. It has a long battery life, because the power consumption is only a fraction of that required by a comparable vacuum-tube set.
The unit employs high-performance, low-cost transistors known as the grown junction n-p-n type. They achieve power gains of 34 and 40 decibels in the intermediate and audio stages, respectively. Previously, such values have been obtained only in the laboratory. Yet only four transistors are used in the entire set, about half the number hitherto employed in laboratory models. One transistor is used as a combination mixer-oscillator; two act as intermediate-frequency amplifiers; one serves as an audio amplifier. A germanium diode is used as a detector.
Offshore Radar Platform.
In the summer of 1955, the first of the U.S. Air Force 'Texas towers' was launched by the Bethlehem Steel Co. at Quincy, Mass. After final inspection and modification, it was towed out to sea and put in place on Georges Bank, about 100 mi. east of Cape Cod. The tower consist of a triangular platform, weighing 6,000 tons, with three long cylindrical legs, one at each corner. The steel platform alone weighs 6,000 tons. It was towed into position with the three legs protruding upward through the platform into the air. When over the chosen site, the legs were lowered through wells in the platform and three powerful hydraulic jacks hoisted the platform to the desired height, 87 ft. above the water level. Each leg is 10 ft. in diameter and approximately 150 ft. long; it is a long column filled with concrete. Paint combined with cathodic protection was used to guard against corrosion. For the surfaces at the level of the tides and spray, a 35-ft. length of Lukens 10 per cent monel-clad steel was used. Monel was selected because of its excellent resistance to the corrosive effects of salt water, spray, and air.
The tower will include housing facilities for the warning and weather-reporting equipment, as well as sufficient shelter for a crew of more than 70 Air Force, Navy, weather, and Coast Guard personnel. Rising from the platform are to be three radomes sheltering the radar antenna and the radio-communications equipment. Power-generating equipment, living quarters for the men, sick bays, and recreation rooms will all be mounted on the platform. Docking facilities for supplying the station have been provided, and there will also be space for helicopter landings.
The tower is the first of several to be erected about 100 mi. off the east coast of the United States by the Navy Bureau of Yards and Docks. The towers are designed to provide the Continental Air Defense Command with adequate warning of approaching enemy aircraft in order to intercept them before they reach coastal targets. In addition they will serve as weather collecting and reporting stations.
Airborne Radar.
In September, 1955, the Air Force Air Research and Development Command released the report of a 'new, compact airborne Sperry radar that assures greater safety for troop carrying transports and essential cargo planes.' This announcement of the APN-59 radar was of particular interest in the light of the recent attention given by commercial airlines to airborne radar as an aid in avoiding bad weather and clearing terrain.
The Armed Services have been vitally interested in airborne radar because of its possible application to bombing, air defense, reconnaissance, and the detection of enemy ships. With today's emphasis on air power, there is a further need by the military for utilizing radar's unique capability as a self-contained navigational aid in any part of the world, in any weather, without recourse to ground assistance. It can also be used in airborne refueling operations and air-sea rescue.
Development.
The navigational radar for such operations is a descendant of the airborne 'search' sets used to combat German submarines in World War II. Development of these early sets followed the refining of microwave techniques. The latter made possible the generation of sufficiently sharp radio beams with antennas small enough to fit aboard aircraft. The set was compact and capable of scanning quickly many square miles of ocean.
In World War II, Sperry co-operated with the Navy and the National Defense Research Council in developing the first X-band Search Radar. Widely used operationally, it was known as the ASD (Airborne Surface Detection). These radar sets owe much of their success in detecting submarines and Kamikase attacks to the foresight of the Navy in requiring beacon facilities in them and in installing ground and shipboard beacons ('Racons'). The beacon function gave pilots the range, bearing, and identity of a runway or carrier beyond normal radar ranges and with only a slight increase in radar complexity.
Capacity of the APN-59.
In 1950 Sperry undertook the development of a 'search' radar that would include the original mapping and beacon functions of the ASD plus a means for effective weather detection and navigation. Such a device had to meet certain requirements: it must give good pictures, not only in coastal areas but also over land — a much more difficult technical problem; it must provide increased radar power for greater range; it must include a means of stabilizing the radar beam against the pitch and roll of the aircraft to give more accurate positional measurements and to avoid losing scope data during aircraft turns. In some modes of operation, directional stabilization of the scope data was required in order to permit the measuring of drift and to make possible the co-ordination of scope data with aircraft-control action. Beacon facilities were required and long transmitter pulse lengths and antenna beam switching had to be incorporated for effective performance against weather.
The radar set, in addition, was required to meet increasingly severe environmental conditions of altitude, temperature, vibration, and shock. Motors had to start in subzero temperatures; the radar had to operate at high altitude in dust-laden atmospheres; the set had to be explosion proof. Space allocation for the APN-59 was less than for any previously conceived airborne radar and its mechanical construction alone presented a formidable problem.
The APN-59, announced in the fall of 1955, was specifically designed to meet these several requirements. During flight tests, the device detected storms 240 mi. away; it demonstrated ground mapping over 100 mi.; it detected ships more than 100 mi. from the aircraft in which it was located.
SPAR.
A lightweight, low-cost, portable radar system was successfully tested in 1955. A ground-controlled approach (GCA), the system is called SPAR for super-precision approach radar and was developed by the Laboratory for Electronics. It is intended for small fields, such as advanced military bases, where mobility and speed of assembly are factors.
SPAR consists of a tripod pedestal on which two small antennas swing to and fro, scanning both the aircraft glide path and the runway location. The complete system weighs about 2,000 lb. so that it can be loaded in a one-ton truck and completely assembled in six hours. Inside the truck an operator can watch two 'blips' or light spots on the radar-scope. The upper blip represents the glide path or descent of the plane; the lower one, the azimuth or directional line-up to the runway. Watching these, the operator can maintain a running conversation with the pilot, giving him landing directions.
SPAR can be reoriented to different runways in less than 10 minutes. The indicator control unit can be operated from a foxhole or a control tower and SPAR can be located from 2,000 to 10,000 ft. from touchdown and 1,000 ft. from the runway center line. It can track an approaching plane with an accuracy of plus or minus 20 ft. of touchdown. The accuracy is 0.5 per cent of all other ranges. When SPAR is combined with an altimeter which provides altitude readings right down to the ground, genuine blind landing will be possible.


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