loran (lôrˈănˌ) [key], long-range, accurate radio navigational system used by a ship or aircraft to confirm or to determine its geographical position. The term loran is derived from the words lo ng- ra nge n avigaton. Loran, operating in the 1,700-kHz range, measures the time-of-arrival difference between two signals transmitted from two geographically separated ground stations. The pulse from the first station, called the master, triggers the second station, called the slave, into transmitting a similar pulse after a set time delay. Knowing the elapsed time difference, the navigator refers to a loran chart and selects his line of position. The chart contains groups of hyperbolic curves of constant time differences between particular station pairs. The position of the receiver (ship or airplane) will be somewhere along the curve that corresponds to the measured time difference. By taking a similar time-difference reading from a second pair of stations whose curves intersect those of the first pair, a definite geographic fix may be obtained.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.