Английский язык: Методические указания и задания к контрольным работам для студентов специальности «Техническая эксплуатация транспортного оборудования», страница 31

 The Loran system makes it possible to determine the position of a vessel by means of 3 or more fixed transmitters and one receiver specially constructed for the job. The emission from the 3 transmitters consists of very accurately synchronized pulses, and the receiver aboard the vessel measures the time differences in arrival of the commonly linked pulses from the transmitters.

The basic principles are:

-  Propagation of radio waves is of constant and known velocity.

-  All points where signals of the same time difference are received, are situated on a line of position forming a hyperbolic line as the time difference expresses the difference in distance to the transmitter.

Using a chart where hyperbolic lines of position are overprinted, the navigator is able to determine one line of position on receiving signals from two pairs of stations. The position is determined by the intersection between two lines of position.

The hyperbolic systems may be divided in two subgroups, depending on the method of measurement;

-  Pulse-time measurement (stations transmitting short pulses).

-  Phase measurements (stations transmitted continuous waves).

The pulse systems have the following advantages:

-  Measurements are accurate.

-  Night effect is of less importance to accuracy and may be used to      extend the range.

-  Many stations may work on the same radio frequency, only varying  the pulse repeating frequency.

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