as follows: A master ground station transnnits signals consisting 

 of short pulses of radio frequency energy on a channel in the 1, 800 

 to 2,000 kc. band. A slave station receives these pulses and uses 

 them to synchronize its transmitter, which in turn transmits simi- 

 lar short pulses of radio frequency energy. The two signals are 

 received aboard a ship or aircraft on a specially designed radio 

 receiver. The difference in time of arrival between the master 

 and slave signals, measured in microseconds, is shown on the 

 receiver. This time difference determines a unique hyperbolic 

 line of position on the earth's surface. The same procedure with 

 another pair of signals provides an additional line of position 

 which is crossed with the first line to obtain a Loran fix. 



Loran-A is useable twenty-four hours a day and is not liinited 

 by weather conditions. Its accuracy is comparable to celestial 

 navigation and is approximately one percent of the distance from 

 the transmitting stations. The limit of groundwave reception is 

 about 700 nautical miles during the day; at night, skywave signals 

 can be obtained up to 1, 400 nautical miles from the stations. 



The U. S. Coast Guard maintains fifty of the sixty-eight Loran- 

 A stations in operational use; eleven more stations are now under 

 construction. Present and proposed Loran-A coverage is confined 

 to the Northern Hemisphere, and groundwave fixing information will 

 soon be available in 30 percent of its water areas; skywave fix and 

 line-of-position information will be available in much of the rest of 

 that area. 



Additional stations could be constructed. Although the receivers 

 are relatively inexpensive, $1,500 - $6,000, the transmitting sta- 

 tions are not. Most of the complexity of the system is incorporated 

 in the shore component, and the average cost per transmitting 

 station is about 1. 3 million dollars. 



Although Loran-A will never fvilly meet the requirement of the 

 oceanwide survey program due to its short range, particularly 

 during daylight hours, it has certain advantages. These are pri- 

 marily that extensive coverage is now available, and that Loran-A 

 receivers are relatively inexpensive, reliable, and require little 

 or no training in their operation. 



Another of the operational Loran systems is called LORAN-C. 

 Like Loran-A, it is a pulsed, hyperbolic, electronic system employ- 

 ing shore-based transmitting stations and specially designed 



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