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Long Range Navigation System "Saitakov" (LORAN-C)

The system of long-range navigation "Saitakov" (LORAN-C)

The international organization ICAO as a standard means of long-range navigation for a long time adopted a system of long-range navigation "Laurent", providing coverage of long distances, particularly airlines, ran over maritime spaces.

The "Saitak" system (US development) is a further development of the "Laurent" system and provides the location of the aircraft with much greater accuracy. High accuracy is achieved due to the phase method of comparing the time of passage of signals from ground stations. In the "Laurent" system, a series of pulses with a standard repetition rate (from 20 to 60 Hz) is transmitted, and the receiver measures the time between pulse reception of individual stations. In order to obtain more accuracy in determining the time interval between pulses arriving from the individual stations of the chain, in the receiving equipment of "Saitak" ("Laurent-C") the high-frequency filling of the pulse series of the master and slave stations is additionally compared. The accuracy of the "Saitak" system is therefore many times higher than that of the "Laurent". The range of the "Saitak" system is also much larger than that of the "Laurent" system.

The work of the Saitak system is similar to the Loran system. The first ground station, called the lead, transmits a pulse, followed by a second and second pulse, which is located at a certain distance, after a certain and known period of time (T interval). From the first. Both signals from these stations will be received by the aircraft receiver at the same interval, provided that the stations are located from it at equal distances. If the aircraft is closer to the first station, then the time interval will be more by the amount of AT (T + DT). If it is closer to the second station, then the interval between the pulses will be smaller by an amount N (r - AT). By measuring the gap between two pulses and comparing it to a known interval, the on-board receiver determines the line passing through the point of the aircraft's location. This line is a hyperbola, the focal points of which are the locations of two transmitting stations.

If a pair of similar pulse pair is transmitted to other, differently spaced stations, one of which may be part of the first pair, the interval between receipt of these two pulses allows to establish a second hyperbola. Crossing the hyperbole on the map Laurent Saitakov will determine MS.

If running third pair of stations is obtained with their help serve hyperbole to test and refine the previous constructions. In reality circuits systems "Laurent" and "Saitakov" master stations have two or three slave, each of the master stations which alternately and in sequence operate on a single frequency.

For the Saitak system ("Laurent-S") to work, it is necessary that Strict synchronization of the moments of emission of pulses from the master and slave stations would be the synchronization of the phase of high-frequency pulse filling. This is done by transmitting the corresponding signals by the master station on the carrier wave. A rough measurement of the time between pulses is performed in the same way as in the Laurent system, which allows us to further eliminate the two-valuedness in the process of accurate determination of distances by the method of comparing the phases of high-frequency pulse filling. Two-valuedness can occur when the phase of the first pulse of the master station is compared with the second pulse of the slave station. Such a method makes it possible to measure the gaps between pulses to within 0,02-0,03 / sec. The resulting error in measuring the time interval of the Laurent-C system is 0,1 μ / s instead of 1 μ / s for the Laurent system.

Operating experience has shown that with this system, the position of the airplane can be determined in 25% of cases with an accuracy of 250 m at distances of about 1500 km from one of three transmitters of the system.

When using ground wave system provides an accurate determination of coordinates at a distance of 2500 km during the day and up to 1800 km at night; using sky-wave system can be used at distances up to 3 200 km during the day and up to 4 200 km at night with an error about 4-5,5 km.

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