A Report on Hyperbolic Navigation System
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A Report on Hyperbolic Navigation System Quiambao, John Vincent Roque, Rommel Sagad, Arjel San Pablo, Aldrin Seth Santos, Johan Christian INTRODUCTION Hyperbolic navigation system A navigation system that produces hyperbolic lines of position (LOPs) through the measurement of the difference in times of reception (or phase difference) of radio signals from two or more synchronized transmitters at fixed points. Such systems require the use of a receiver which measures the time difference (or phase difference) between arriving radio signals. Assuming the velocity of signal propagation is relatively constant across a given coverage area, the difference in the times of arrival (or phase) is constant on a hyperbola having the two transmitting stations as foci. Therefore, the receiver measuring time or phase difference between arriving signals must be located somewhere along the hyperbolic line of position corresponding to that time or phase difference. If a third transmitting station is available, the receiver can measure a second time or phase difference and obtain another hyperbolic line of position. The intersection of the lines of position provides a two-dimensional navigational fix .User receivers typically convert this navigational fix to latitude and longitude for operator convenience. HISTORY The theory behind the operation of hyperbolic navigation systems was known in the late 1930’s, but it took the urgency of World War II to speed development of the system into practical use. By early 1942, the British had an operation hyperbolic system in use designed to aid in long range bomber navigation. This system, named Gee, operated on frequencies between 30 MHz and 80 MHz and employed “master” and “slave transmitters” spaced approximately 100 miles apart. The Americans were not far behind the British in development of their own system. By 1943, the U.S. Coast Guard was operating a chain of hyperbolic navigation transmitters that became Loran A (The term Loran was originally an acronym for Long Range Navigation). By the end of the war, the network consisted of over 70 transmitters providing coverage over approximately 30% of the earth’s surface. In the late 1940’s and early 1950’s, experiments in low frequency Loran produced a longer range, more accurate system. Using the 90-110 kHz band, Loran developed into a 24-hour-a-day, all-weather radio navigation system named Loran C. From the late 1950’s, Loran A and Loran C systems were operated in parallel until the mid 1970’s when the U.S. Government began phasing out Loran A. The United States continued to operate Loran C in a number of areas around the world, including Europe, Asia, the Mediterranean Sea, and parts of the Pacific Ocean until the mid 1990’s when it began closing its overseas Loran C stations or transferring them to the governments of the host countries. This was a result of the U.S. Department of Defense adopting the Global Positioning System (GPS) as its primary radio navigation service. In the United States, Loran serves the 48 contiguous states, their coastal areas and parts of Alaska. It provides navigation, location, and timing services for both civil and military air, land, and marine users. Loran systems are also operated in Canada, China, India, Japan, Northwest Europe, Russia, Saudi Arabia, and South Korea. CONSOLE Although hyperbolic systems as such, were never pursued to completion in Germany, Dr. Ernst Kramar, working at Standard Elektrik Lorenz in 1938, developed an improved version of the American Radio Range which was able to provide multiple fixed equisignals for defining multiple routes (Elektra). After German military use early in W.W. II, Dr Kramer was asked whether he could improve it to provide directional information between the equisignals. He did so, and it was re-named Sonne, after a character from the operas. Consol is actually the name the British assigned to the system. There were also to have been other versions known as Mond (Moon) and Stern (Star) operating at other frequencies. Dr. Kramar has related how, being a devotee of Richard Strauss's music (hence Elektra), he wished to name it Salome but was overruled by the Luftwaffe. This system was installed in Norway, France and Spain as a navaid for German aircraft flying the circuitous route over the Atlantic between France and Norway, and their U-boats. It is an example of a 'collapsed' hyperbolic system wherein the baseline between the transmitting aerials is made so short that the hyperbolae degenerate into radials at a very short distance and the system becomes a bearing system rather than a hyperbolic one. During WWII, the British captured some Sonne charts and took them to Group Capt Dickie Richardson, who was the navigation officer for Coastal Command at Northwood. Capt Richardson then found a receiver and tuned in getting a good bearing on his location. He then decided that what was good for the Germans would be good for the British. so he ordered the RAF map department to manufacture charts to British specifications. Dickie called the system CONSOL meaning "by the sun" which is described in his book "Man is Not Lost". Sonne/Consol used three aerials spaced on a line 1.5 miles long, or about three wavelengths at the operating frequency of 300 kHz. An identical signal was fed to all three aerials but at one outer aerial, it was delayed by 90 degrees of phase while at the other outer aerial it is advanced by 90 degrees. Multiple lobes with deep nulls between them were produced by the interaction of the three aerials. By steadily changing the phase shift in the two outer aerials so that it interchanged every 30 seconds, these lobes were caused to sweep. They were also switched at a very much faster rate in synchronism with a Morse pattern of dots and dashes, the effect being that each lobe carried only either dots or dashes and was replaced by its complement over the 30 second period. Consol ground station block diagram. The navigator only needed an ordinary radio receiver tunable to 300 kHz in order to use the system.. He heard a series of dots slowly merging into a steady tone and then becoming a series of dashes (or -dashes becoming dots). He simply had to count how many dots or dashes he could hear before the steady tone and then plot his position line on a suitably overprinted map. There were multiple ambiguities in the system since there was no inherent way of distinguishing between one lobe and another. At its narrowest each lobe, it was only about 7.5 degrees wide. They were resolved either by approximate knowledge of position or by taking a loop bearing on the station. For this purpose, a steady tone was transmitted for a few seconds before each sweep, from the central aerial only. One station did not provide a fix, of course, but it was a very useful system requiring little expertise to use and only simple equipment. Consol was one of the recommended ICAO navaids after WW II. Additional transmitters were installed near New York, San Francisco, in the USSR, and in the UK (Bush Mills in Northern Ireland). RAF navigators found the system of considerable value, and it had the curious distinction of being a wartime navaid used by both sides simultaneously. There is even a story that at one time the Germans had problems with their Spanish transmitter and could not get spares to it, so the British supplied the Spanish with the necessary items in order to get the station back on the air for Coastal Command's benefit. GEE NAVIGATION SYSTEM Watson-Watt's demonstration in 1935 of the possibilities of radar for detecting aircraft caused considerable work to be put in hand in the UK on the development of high power pulse transmitters and, of equal importance, methods of presenting aircraft returns to operators. It could only be done by visual presentation and it required the design of stable, accurate time bases for cathode ray tubes. In 1935, good cathode ray oscilloscopes (or oscillographs as they were called) were still laboratory instruments and were by no means widely available or cheap. The few television sets then available were expensive, virtually hand-made and unreliable. One major and common problems in designing any hyperbolic navigation system was the measurement of time. Since no means of directly measuring a millionth of a second was available in that era, it forced designers to use continuous-wave phase comparison with its attendant problem of ambiguity. Once it became possible to transmit very short pulses, the possibility of designing an unambiguous system was realized immediately. But there was another stumbling block. There was no way of measuring short time intervals that could be used in an operational system by relatively unskilled operators. DEVELOPMENT It was the development of reliable cathode ray tubes and their associated time bases that provided the solution. In October 1937, R. J. Dippy, who was on Watson-Watt's staff at the time, conceived a system using pulse transmitters and a cathode ray tube display that would measure the difference in time of arrival of two pulses sent out from two transmitters placed about ten miles apart and with a baseline at 90 degrees to a runway. Synchronized pulses would be sent out from both transmitters and the delay between reception of them would be seen on the CRT display. When there was no delay they would be seen as a single pulse and the aircraft would be on the right bisector of the baseline; in other words, lined up with the runway. If it was off course, one way or the other, there would be a delay and, by identifying which of the two pulses was leading, the pilot could tell on which side of the runway he was and turn accordingly.