LORAN

abbreviation of long-range navigation system of navigation developed for marine and air navigation. Lines of position are determined by noting differences in time of reception of synchronized pulses from widely spaced transmitting stations, master and slave. A master station broadcasts an uninterrupted series of pulses of fixed duration and at a fixed rate (e.g., of 50 microseconds' duration at a rate of 25 pulses per second). A slave station, 200300 miles (320430 kilometres) away, automatically transmits its own signals, maintaining a frequency and pulse duration in accord with those of the master station. The slave station maintains a fixed time difference between its reception of the master signal pulse and the sending out of its own. The noted time difference of arrival of the two pulses locates the craft somewhere on a curve (hyperbola) every point of which differs in distance from master and slave station by the same amount (e.g., is three miles further from master than from slave). Tuning in a second slave station locates the craft on another hyperbola, so its exact position can be fixed at the intersection of the two. A mobile loran system, used for determining distances between a navigating master station (interrogator) and slave stations located along the shore, is known as EPI (electronic position indicator). Related systems, as decca and dectra, use continuous signals rather than pulses, differences in distances from master and slave stations being determined by noting wave-phase differences rather than time differences.