- 4 December 2020
Cosa vuol dire LORAN? [d] In any given location it was common to be able to receive more than three stations at a time, so some other means of identifying the pairs was needed. This led to the decision to open Loran-C to civilian use in 1974.. This was due largely to two important factors. It was first used for ship convoys crossing the Atlantic Ocean, and then by long-range patrol aircraft, but found its main use on the ships and aircraft operating in the Pacific theater during World War II.  The Canadian liaison was required, as ideal siting for the stations would require several stations in various locations in the Canadian Maritime Provinces. Vogliamo garantire un’informazione di qualità anche online. , LORAN was soon ready for deployment, and the first chain went live in June 1942 at Montauk and Fenwick. By the end of World War II there were 72 LORAN stations, with over 75,000 receivers in use. Loren. This test demonstrated accuracy of ½ mile, significantly better than normal LORAN. Scopri il significato di 'loran' sul Nuovo De Mauro, il dizionario online della lingua italiana. The AN/APN-4 was quickly supplanted by the AN/APN-9 of 1945, an all-in-one unit combining the receiver and display of greatly reduced weight. One was that the electronics needed to read a Loran-C signal were complex, and in the era of tube-based electronics, physically very large, generally fragile, and expensive. Loran-A was dismantled starting in the 1970s; it remained active in North America until 1980 and the rest of the world until 1985.  This entire procedure was then repeated for a second master-secondary set, often the second set of the same chain but not always. At night these signals were suppressed and the range dropped to 350–500 nautical miles (650–930 km). It is not to be confused with. One might receive a two-bounce skywave from one station at the same time as a three-bounce wave from another, making interpretation of the display quite difficult. As the signal was repeating, these spikes appeared many times across the width of the display. Known as Skywave-Synchronized LORAN, or SS LORAN, the system provided coverage anywhere south of Scotland and as far east as Poland with an average accuracy of one mile. Using cycle matching, the system demonstrated an accuracy of 160 feet (49 m) at 750 miles (1,210 km). Loran-A used two frequency bands, at 1.85 and 1.95 MHz. , LORAN was a simple system that compared the arrival times of pulses to make a measurement. Accuracy was more a matter of signal quality and operator experience than any fundamental limit of the equipment or signals. Measurement times on the order of three to five minutes were typical, requiring the navigator to take into account the motion of the vehicle during this time. Two frequency bands were initially selected, 1.85 and 1.95 MHz for nighttime use (160 meters), and 7.5 MHz (40 meters).  Several foreign chains in both the Pacific and Atlantic followed suit, and by 1985 most of the original chains were no longer operational. A system with three transmitters was set up on the US east coast using long antennas supported by balloons. This system shared the middle tower, which broadcast on both frequencies. By combining the two concepts, envelope timing and phase comparison, both of these problems could be eliminated. , The same basic concept was also tested post-war by the Coast Guard in a system known as "Skywave Long Baseline LORAN". [e] The amplified signal from the stations would also appear on the display, highly compressed in time so that it displayed as a series of sharp spikes (blips). , The nighttime mode of operation was a perfect fit for RAF Bomber Command. Dippy convinced them that an airborne version was definitely possible, leading to some interest by the U.S. Army Air Force. TS aer., mar. Extensive evaluation flights revealed an average error of 1–2 miles (1.6–3.2 km). These locations are separated radially around the station, meaning a fix might be within a given radial direction or a fixed distance to either side. The intersections of the two sets of curves normally result in two possible locations. This system, later known as Loran-B, ran into significant problems (as did another Air Force system, Whyn and a similar British system, POPI). Among these, he outright demanded that the airborne LORAN receivers be built physically similar to the Gee receivers, so that they could be swapped out in service simply by replacing the receiver unit.  But it was also discovered that the system was very difficult to use and the measurements remained subject to confusion over which cycles to match. In practice, a fixed time is added to account for delays in the receiver electronics. At that point, measurement starts. Further, as military ships and aircraft moved from Loran-A to Loran-C, the older receivers were made surplus. At setting 5, the pips on the scale represent differences of 10 microseconds, and the operator measures the distance between positions. Each pair broadcast on one of four frequencies, 1.75, 1.85, 1.9 or 1.95 MHz (as well as the unused 7.5 MHz). The difference as measured at each of these settings is then added up to produce the total delay between the two signals. LORAN, short for long range navigation, was a hyperbolic radio navigation system developed in the United States during World War II. Dispositivo grazie al quale le navi e gli aerei possono determinare, con sufficiente precisione, la propria posizione con rilevamenti su stazioni radio-trasmittenti sistemate a terra. He stated that he was aware of similar work in the UK, but didn't know enough about it to offer any suggestions. Decca referred to these radial areas as "lanes", and used a mechanical system to keep track of which one the receiver was in.. , Although LORAN deliberately used the same display as Gee in order to share equipment, the signals were so much longer and more complex than Gee that direct measurement of the two signals was simply not possible. The widespread introduction of inexpensive microelectronics during the 1980s caused Loran-C receivers to drop in price dramatically, and Loran-A use began to rapidly decline. , During early experiments with LORAN's skywaves, Jack Pierce noticed that at night the reflective layer in the ionosphere was quite stable. This proved to be extremely successful, with test-runs placing the aircraft within 10 yards of the target. Dippy also designed the ground station timing equipment. This was joined shortly thereafter by two stations in Newfoundland, at Bonavista and Battle Harbour, and then by two stations in Nova Scotia, at Baccaro and Deming Island. This led to the possibility that two LORAN stations could be synchronized using skywave signals, at least at night, allowing them to be separated over much greater distances. Mixed into the signal is an electronic scale produced in a time base generator, causing a series of small pips to appear over the now-inverted original signals. Trova il 8 significato della parola LORAN. The U.S. Coast Guard took over operations of both systems in 1958. The only way to express the accuracy was to measure it in practice; average accuracy on the route from Japan to Tinian, a distance of 1,400 miles (2,300 km), was 28 miles (45 km), 2% of range. [b] Orders for initial systems were sent out at a follow-up meeting on 20 December 1940. They refused, and the hostess then asked if they drank. British nomenclature used "cursor" instead of "pedestal". , A receiver listening for these signals and displaying them on an oscilloscope will see a series of "blips" on the display. But by isolating the expensive portions of the system at the few broadcast stations, the Decca Navigation System using this technique went active in 1944, offering accuracy similar to Gee but using low-cost mechanical displays which were also much easier to use. For instance, the three stations on the Hawaiian Islands were arranged as two pairs 2L 0 and 2L 1. , In comparison, LORAN was deliberately designed to allow skywaves to be used, and the resulting received signal was far more complex. A final major expansion took place in Portugal and the Azores in 1965, offering additional coverage to the mid-Atlantic.  In order to take a fix, the receiver takes two measurements based on two different master/secondary pairs. You could be comparing the first waveform from one station to the first from another, but the second waveform looks identical and the operator may line up those two waves instead. For instance, a receiver might measure the distance between the two blips to represent a delay of 0.5 ms. Tutti i tipi di parole sono accettati. At the time the project was being driven primarily by Captain Harding of the U.S. Navy, and they were concentrating entirely on a shipboard system. Receiver units improved greatly over time. Accordingly, the LORAN operator set the delays so the master signal appeared on one trace and the secondary on the second, allowing the complex patterns to be compared. Automated receivers became available in the 1950s, but the same improved electronics also opened the possibility of new systems with higher accuracy. RAF Coastal Command had another station installed in Shetland, offering coverage over Norway, a major staging ground for German U-boats and capital ships. The system was declared operational in 1957, and operations of LORAN and Cyclan were handed to the U.S. Coast Guard in 1958. It was physically identical to the UK's two-piece Gee set, and could be easily interchanged with these units. The decision was made to abandon the current efforts, use Gee on their own aircraft, and re-develop their system for the long-range role instead. Con un unico abbonamento hai la rivista di carta e tutte le versioni digitali.  These lower frequency systems were found to be much more stable electronically. LORAN adopted the use of varying the pulse repetition frequency (PRF) for this task, with each station sending out a string of 40 pulses at either 33.3 or 25 pulses per second. When the signal is sent, this station, the "master", sends out its transmission. , By this time the team had become aware of the UK's Gee efforts, and were aware that Gee used a system of electronically generated strobes that produced pips on the display that were accurately aligned with system timing. This limited use to the military and large commercial users. , The enormous distances and lack of useful navigation points in the Pacific Ocean led to widespread use of LORAN for both ships and aircraft during the Pacific War. By the early 1970s such units were relatively common, although they remained relatively expensive compared to devices like a radio direction finder. This station is equipped with a receiver, and when it sees the signal from the master arrive, it triggers its own transmitter. It was first used for ship convoys crossing the Atlantic Ocean, and then by long-range patrol aircraft, but … The goal was to perfectly align the two traces.. , Additional chains in the Pacific were added in the post-war era. The four test stations were dismantled and shipped across the Atlantic, and re-installed to form two chains, Aberdeen-Bizerta, and Oran-Benghazi. , In the case of Gee, signals were direct from the transmitter to receiver, producing a clean signal that was easy to interpret. , Moreover, the complex series of received signals considerably confused the reading of the LORAN signal, requiring some interpretation. , During this same period, the U.S. Army Air Force became interested in a very-high accuracy system for bombing pinpoint targets. Regalati o regala Internazionale. , Loran-A continued to improve as the receivers were transistorized and then automated using microcontroller-based systems that decoded the location directly. This led to a second round of tests in late 1943, this time using four stations, Montauk, East Brewster, Massachusetts, Gooseberry Falls, Missouri, and Key West, Florida. This would prove extremely useful; RAF Transport Command aircraft could swap their receivers when moving to or from the Australian theatre.  The PRF could be adjusted from 25 to 25 and 7/16th for Low, and 33 1/3 to 34 1/9th for High. It was similar to the UK's Gee system but operated at lower frequencies in order to provide an improved range up to 1,500 miles (2,400 km) with an accuracy of tens of miles. , A test system was first attempted on 10 April 1943 between the LORAN stations at Fenwick and Bonavista, 1,100 miles (1,800 km) away. The U.S. Air Force worked on a different concept, Cyclan, which the Navy took over as Loran-C, which offered longer range than LORAN and accuracy of hundreds of feet. In particular, the accuracy offered by LORAN allowed aircraft to reduce the amount of extra fuel they would otherwise have to carry to ensure they could find their base after a long mission. But instead of broadcasting a continuous signal, as in the case of Decca, the signal would be in the form of pulses. The experiments demonstrated that the inaccuracy inherent to the design while working at such low frequencies was simply too great to be useful; operational factors introduced errors that overwhelmed the capabilities. Dippy also instituted a number of simple changes that would prove extremely useful in practice. Operations were identical to "normal" LORAN, but it was often assumed charts would not be available and would have to be prepared in the field. Significato: Vedi Lorena: di recente diffusione, si afferma infatti solo verso la metà del XIX secolo e dimostra la stima e la fedeltà nei confronti dei granduchi di Toscana, molto aperti e innovatori. Aiutaci e aggiungi una parola. Aiutaci e aggiungi una parola. This is repeated for setting 6 at 50 microseconds, and again at setting 7 at 500 microseconds. , Project 3 moved to the newly formed Radiation Laboratory's Navigation Group in 1941. At night, as many as thirty different skywaves might be received from a single transmitter, often overlapped in time, creating a complex return pattern. Si tratta di una forma femminile del nome Lorne, creata ad hoc dallo scrittore Richard Doddridge Blackmore per la protagonista del suo romanzo del 1869 Lorna Doone.Principalmente grazie al romanzo si è diffuso il suo uso come nome proprio di persona.. Onomastico. To illustrate the basic concept, this section will consider the pulse method only. This process was repeated at sweep speed 3, at which point only a selected part of the signal was visible on the screen. Puoi anche aggiungere una definizione per LORAN, sigla per Long Range Navigation, o meglio navigazione a lungo raggio: il termine indica un sistema di navigazione elettronica per determinare la posizione basandosi sulle differenze dei tempi di ricez [..], : (s.m.) Long Range Aid to Navigation. Japanese systems remained on the air longer, until 1991, serving their fishing fleet. As part of this exchange, the Project 3 team also found that Gee was almost identical to their own system in concept and desired performance. The operator would then use the intensity and focus controls to fine tune the signal and provide a sharp display. Chains were also installed in China, prior to the ultimate end of the Chinese Communist Revolution, and these stations remained on the air at least into the 1990s.  On the receiving end, a station wagon was fitted with a simple receiver and sent around the country looking for solid signals, which were found as far away as Springfield, Missouri. The project was still top secret at this time, and little actual information was shared, especially with the Coast Guard. Thus at short distances the lines cross at angles close to 90 degrees, and this angle steadily reduces with range. General operation started by selecting one of nine stations, labeled 0 to 8, and setting the sweep speed to 1, the lowest setting. If displayed on a single CRT trace, the operator would see a string of sharp "blips", first the master, then one of the secondaries, the master again, and then the other secondary.  Additional stations all along the U.S. and Canadian east coast were installed through October, and the system was declared operational in early 1943.  This increases the amount of room on the scale by a factor of π for any given display size, improving accuracy. Initial tests were carried out in May 1944 between Chatham, Massachusetts, and Fernandina, Florida, and a second set between Hobe Sound, Florida, and Point Chinato, Puerto Rico, in December–January 1945–46. Nevertheless, the three transmitters were re-installed in northern Canada and Alaska for experiments in polar navigation, and ran for three years until shutting down again in March 1950. This is actually quite easy to perform using simple electronics and can be displayed directly using a simple mechanical pointer. Mobile LORAN was another lightweight system, mounted on trucks. , At the lowest sweep speed, the system also produced a local signal that was fed into the display and produced a sharply defined "pedestal", a rectangular shape displayed along the two traces. Since phase comparison is generally more accurate at low frequencies due to details of the electronics, taking accurate fixes would be based on this technique. Con il tuo contributo potremo tenere il sito di Internazionale libero e accessibile a tutti. , At a 1 October 1940 meeting of the U.S. Army Signal Corps' Technical Committee, Alfred Loomis, chair of the Microwave Committee, proposed building a hyperbolic navigation system. Chinese systems were active into the 1990s before their replacement with more modern systems, and their nine chains were still listed as active in Volume 6 (2000 edition) of the Admiralty List of Radio Signals. As the mission changed from short-range tactical bombing to over-the-pole nuclear delivery, the (newly formed) U.S. Air Force lost interest in the concept. , The original airborne receiver unit was AN/APN-4 unit of 1943. The U.S. Navy began development of Loran-B, which offered accuracy on the order of a few tens of feet, but ran into significant technical problems. By the late 1970s, the Coast Guard was in the midst of phasing out Loran-A in favor of additional Loran-C chains. This was due largely to the large numbers of surplus Loran-A units released from the Navy as ships and aircraft replaced their sets with Loran-C. , There is an entirely different way to accomplish the same timing measurement, not by comparing the timing of the pulse envelopes, but timing the phase of the signals. It was similar to the UK's Gee system but operated at lower frequencies in order to provide an improved range up to 1,500 miles with an accuracy of tens of miles. Using some other form of navigation, dead reckoning for instance, one of these possible positions can be eliminated, thus providing an exact fix. , For a production system, the team began working with a system using a circular J-scope display for improved accuracy. , In mid-1942, Robert Dippy, the lead developer of the Gee system at the Telecommunications Research Establishment (TRE) in the UK, was sent to the US for eight months to help with LORAN development. In spite of the dramatically improved performance of Loran-C, LORAN, now known as Loran-A (or "Standard LORAN"), would become much more popular during this period. These would be used to make a rough fix using the same technique as Gee or LORAN, positively identifying the lane. The groundwave remained fairly sharp, but could be received only at shorter distances and was primarily used during the day. Because the accuracy of the fix depends on the crossing angle, all hyperbolic navigation systems grow increasingly inaccurate with increasing range. By the end of that year additional stations had been installed in Greenland, Iceland, the Faroe Islands and the Hebrides, offering continuous coverage across the North Atlantic. Cosa vuol dire LORAN? Since the pattern depended on the atmospherics between the transmitter and receiver, the received pattern was different for the two stations. Gee CRTs were built to be able to display two traces, and by tuning several delay circuits, the operator could make the first master-secondary signal appear on the upper display and the second on the lower. Avvertenze per la consultazione del dizionario, Il Nuovo vocabolario di base della lingua italiana. (Strumentazione) loran Sistema in grado di calcolare e fornire le coordinate geografiche del punto dove e' posizionata l'antenna ricevente del sistema stesso, con una precisione di qualche migl [..]. They sent a team to the UK to learn about the strobe concept, and immediately adopted it for their work. 1 ms later that signal arrives at the second station, the "secondary". By measuring the distance between them, the delay between the two signals can be calculated.  Early systems operated around 30 MHz, but it was later decided to try experiments with different equipment that could be tuned from 3 to 8 MHz. A spurt in construction followed the opening of the Korean War, including new chains in Japan and one at Busan, Korea. See Bowen's "Radar Days", p. 183. Argyle were discussing the matter with the husband, a third visitor arrived and he offered the men cigarettes. , The decision to switch to the long-range role meant that the high accuracy of the Gee system was not needed, which greatly reduced the need to address the timing problems. , This article is about LORAN. The sharpness of the envelope is a function of the frequency, meaning the lower-frequency systems like LORAN will always have longer envelopes with less well-defined start and stop points, and thus generally have less accuracy than higher-frequency systems like Gee. The more common A-scope represents distances across the diameter of the tube, while the J-scope presents this as the angle around the cathode ray tube's face. The trick to such a system is to ensure the master and secondary stations are phase-coherent, a complex proposition during World War II.  At that time, the original LORAN became Loran-A or standard LORAN, and the new system became Loran-C.[c], In spite of the greatly increased accuracy and ease-of-use of Loran-C, Loran-A remained in widespread use. The missing member appears to be 1.75 MHz. After first considering setting up transmitters on mountain peaks, the team instead settled on two abandoned Coast Guard stations at Montauk Point, New York, and Fenwick Island, Delaware. Even the initial signal from the master station was spread out in time with the initial groundwave signal being sharp (if received), while the skywave receptions could appear anywhere on the display. When two such signals from a single chain are considered, the resulting pattern of lines becomes increasingly parallel as the baseline distance becomes smaller in comparison to the range. A Japanese chain remained on the air until 9 May 1997, and a Chinese chain was still listed as active as of 2000. The only problem from a development standpoint would be selecting frequencies that allowed reasonably accurate pulse envelopes while still having measurable waveforms within the pulses, as well as developing displays capable of showing both the pulses as a whole, and the waves within them. The Aleutian and Hawaii chains shut down on 1 July 1979, the remaining Alaska and West Coast chains on 31 December 1979, followed by the Atlantic and Caribbean transmitters on 31 December 1980. Ideally, perfectly formed rectangular blips would be displayed on the CRT, whose leading edge could be compared with a high degree of accuracy. This led to the "Precision Navigational Equipment for Guiding Airplanes" specification, which was sent back to the Microwave Committee and formed up as "Project 3". However, other sources illustrate that other projects at the Rad Lab were known by number, for instance, the effort to develop a microwave air-to-air radar was Project 1, and a ground-based anti-aircraft system was Project 2. This reduced fuel load allowed the bombload to be increased. Inserisci email e password per entrare nella tua area riservata. Sistema di navigazione a grande distanza dove la posizione è determinata dagli intervalli di tempo fra i segnali ad impulso ricevuti da trasmettitori molto distanti fra [..], Il LORAN (LOng RAnge Navigation, dall'inglese navigazione a lungo raggio) è un sistema di radionavigazione terrestre tramite onde radio LF (a bassa frequenza) che sfrutta l'intervallo di tempo tra i [..], sigla per Long Range Navigation, o meglio navigazione a lungo raggio: il termine indica un sistema di navigazione elettronica per determinare la posizione basandosi sulle differenze dei tempi di ricezione di segnali radio emessi contemporaneamente da più stazioni di riferimento; attualmente è utilizzato il sistema Loran C, un perfezionamento dell [..]. The system was not put into operation, due to a lack of suitable frequency allocations. Gli abbonati hanno accesso a tutti gli articoli, i video e i reportage pubblicati sul sito. At the time, the procedure for generating sharp pulses of signals was in its infancy, and their signals were considerably spread out in time, making measurements difficult. Four frequencies are listed in the Navy documentation, but almost all sources refer to only three. In practice, the transmitters cannot turn on and off instantly, and due to a variety of factors the resulting blips are spread out in time, forming an envelope. A number of sources quote one of the LORAN researchers stating that the effort was actually known as "Project C", not 3. But the improvement of electronics through this period was so rapid that it was only a few years before Loran-C units of similar size and cost were available. Puoi anche aggiungere una definizione per LORAN ... Nome: E-mail: (*facoltativo) Email confirmation: << LINEA DI FEDE: LOSSODROMICA >> Significato-definizione.com.
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