Distance measuring radio navigation system
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Distance measuring radio navigation system

Distance measuring radio navigation system

Rangedifference of long-range navigation systems belong to measuring the propagation time of radio waves from two fixed points on the Earth's surface - ground stations system- to the aircraft. As measured by the difference between the propagation of radio waves is determined by the difference between the distances to the ground stations and the line position of the aircraft.

With two pairs of ground stations are determined by the provisions of the two lines, the intersection of which is the seat of the plane (MS).

Pulse rangedifference systems allow to solve the following navigation problem:

  • a) perform path control by determining the line of the position or position of the aircraft;
  • b) take the aircraft to a given area;
  • c) determine the navigation elements of the flight.

In these systems, the position of the aircraft lines are two hyperbole and so are also the name of hyperbolic systems.

Naturally, to obtain two lines of position, you must have two pairs of transmitting stations. However, a hyperbolic surface equipment system may consist of just three stations, of which one is master station A for both pairs (A-B and A-C) and the other two (B and C) - the slave.

The three ground stations A, B and C form two base AB and AC. Databases located in such an embodiment relative orientation, called the combined databases.

Other variants of the relative orientation of the bases. Databases can be spaced, overlapping, combined with two or three or disposed chain in which several stations are leading.

The operating principle of a hyperbolic system is reduced to a certain period of time between the receipt of an airplane pulses emitted by a leading ground station A and one of the slave stations - B or C. This corresponds to the time difference is a definite difference in the distances from station A and B (or C):

Hyperbole is the locus of points, the difference of whose distances from the foci is constant hyperbole. Hyperbole, the focus of which are located ground station, is a line of position. It is determined by priemoindikatornogo device located on the aircraft over a measured time difference. The second line is determined by the position of the second pair of stations.

Navigation problems are solved on a special map with grids hyperbole, applied "by the points calculated using geodetic formulas.

If you move the plane in space along a certain line position measured by the difference between the arrival time of the plane pulses from master and slave stations Al remains constant. If samoletovozhdenie carried out at relatively short distances within 1000 km, then the nature of the curvature of the lines of the provisions of the Earth's surface has no significant effect and can be neglected. In this case, the lines will position the aircraft family of hyperbole.

Points location of ground stations at points A and B are the focus, and the difference between the measured distances - real axes. If both stations A and B emit signals at the same time, the state line will be a hyperbole, it degenerated into a straight line perpendicular to the base in the middle of it.

When the plane is removed from this straight line - the "zero" hyperbola to the left - the pulses from station A will arrive at the receiving device of the aircraft earlier than the pulses sent by station B, whereas when the plane is moved to the right of the "zero hyperbola, the pulses from station B reach it Before the pulses from station A. If the measured interval is considered positive when the plane is deflected to the left, and if the deviation to the right is negative, then, naturally, the maximum absolute value will reach the interval when the aircraft is on On the straight line that is the continuation of the base, behind station A or station B. Provided that the left of the "zero" hyperbola, the measured time difference Am is considered positive, and to the right - negative, on the continuation of the base to the left. In order to make the digitization of hyperbolas convenient in practical work, especially when performing interpolation between hyperbolas, delays are added to the slave stations, which supplement the counts on the applied hyperbolas to values ​​that are a multiple of ten.

In addition, the slave stations introduces additional, so-called code delays, which increase the count by the amount.

This value is in airplane receiving and display system is taken into account automatically.

Alignment of the stations as follows: A master station controls the operation of the slave station B, which emits pulses after receiving signals from the master station, ie. E. Delayed. This ensures synchronous operation of both stations. However, the slave station emits signals are not exactly at the moment of arrival of pulses from the master station, and with some delay. This delay has two components: a constant and a variable g0 - code delay. First introduced to when taking an airplane can be distinguished pulses pulses from station A station B.

The second delay is to change the sampling line position (hyperbole) of certain regulations.

Thus, a system consisting of a pair of stations does not allow to identify the MS, as determined on the basis of one line, only one position.

To determine the MS should use two pairs of stations (or three stations, one of which - the total lead) arranged so that the line position of the first and second pairs intersect.

On the mechanisms of counting airborne transceiver countdown indicator made room hyperbole - line position of the aircraft.

Fitting plane can be determined over the whole area where the tapped signals of terrestrial stations, with the exception of non-working zones, which are located on the focal axis from foci in the direction opposite the "zero" hyperbola. Non-working area limited to the first branch of the hyperbola given family.

In practice, the accuracy of the system is different in different directions. Close proximity to the perpendicular drawn through the middle of the base, the highest accuracy, but the distance from this perpendicular line and falls, which is a continuation of the base, so low that the system is virtually impossible to use.

In general, difference-ranging radionavigation systems provide high accuracy. determine the location of the movable object and at the same time rationally at selected wavelengths have a greater range. Therefore, these systems are used primarily as a means for further navigation.

Alternative location system, in which the stations form a chain extending along the coastline, provides navigation in the vicinity of a large water basin. Therefore hyperbolic systems are widely used in the development of transoceanic flights.

Another advantage of these systems is unlimited bandwidth and the absence of the transmission device on the plane.

The disadvantages of the system can be considered as the complexity and awkwardness of the ground equipment, as well as the need to strictly maintain the synchronous operation of the stations.

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