LORAN - The Principle Of Loran, Interpreting Loran Measurements, Sources Of Loran Measurement Error, After Loran C

LORAN (Long Range Navigation) is a radio-based navigational aid first used during World War II to locate ships and planes with greater accuracy than could be achieved with conventional techniques. LORAN determines location by comparing accurately-synchronized powerful radio pulses originating from different reference transmitter sites. Pulses from nearby transmitters arrive earlier than pulses from distant transmitters since radio signals travel at a constant speed.

At least three different LORAN signals must be received to determine latitude and longitude. In practice, the distance to more than the minimum three LORAN signals increases accuracy.

The first LORAN systems were in use before computers were sophisticated enough to perform the complex calculations needed to process the timing comparisons. Early LORAN installations required highly-skilled operators to interpret the radio pulses. A half century later technical innovations eliminated the need for much of the skill once required to use LORAN for navigation.

LORAN has evolved through three distinct phases, LORAN A, LORAN B, and the present version, LORAN C. The A and B versions were designed for navigational assistance over relatively short distances. LORAN A and LORAN B transmissions operated in a range of frequencies just slightly higher than the standard AM broadcast band in the United States. The present version, LORAN C, is assigned to 100 kHz, is a frequency well below the AM standard broadcast band. 100 kHz, a frequency where long-distance radio propagation is very dependable. In contrast to LORAN A and LORAN B, LORAN C is reliable over distances of many hundreds of miles.