great as 1,200 nautical miles. The Loran-C is the only loran system 

 now in use by the Hydrographic Office for survey work. 



When the present experimental equipment incorporated into the 

 Loran-C system has been made more reliable, it is expected that the 

 system will have a repeatability on the order of about one foot per mile 

 of distance from the shore stations. It is, however, very sensitive to 

 distortion from overland transmission and requires a sophisticated 

 calibration procedure to determine predictability and overall system 

 accuracy. Another drawback is the large and complex shore installation 

 required, which includes a 625-foot transmission tower. It is consid- 

 ered that the system is not well adapted for use at scales larger than 

 1:50,000. 



3. Ranging systems 



a. Shoran 



This is an interrogator-transponder system that uses the 

 UHF band (200 to 300 megacycles). The range is restricted to approx- 

 imately line-of- sight distances, but good accuracy is available to 

 several users. Position is determined by measuring the time required 

 for the high frequency signal to travel from the mobile station to the 

 transponder and return. Two fixed, shore stations are required, and 

 several mobile stations can use the same two fixed stations. Lines 

 of position are concentric circles. Accuracies on the order of 30 to 

 50 feet and ranges as much as about 40 nautical miles can be obtained 

 depending upon the elevations available for the shore stations. This 

 system is not particularly sensitive to distortion caused by overland 

 transmission. 



b. Electronic Postion Indicator (EPI) 



This system is an interrogator-beacon system that uses either 

 1,850- or 1,950-kilocycle frequencies. It requires a mobile master 

 station and two fixed shore stations. Position is determined by measur- 

 ing the time required for the signal to travel from the mobile master 

 to the shore station and return. Two mobile master stations may use 

 a pair of shore stations on a time- sharing basis. The obtainable range 

 is from 12 to 400 nautical miles, and the accuracy ranges from about 

 135 feet in the best part of the area to about 1,500 feet near the outer 

 limit. The lines of position are concentric circles. Although the system 

 requires continual calibration, it is considered to be excellent for 

 exploratory surveys but shouldnot be usedat scales larger than 1:80,000. 

 The distance measured between the master and a shore station must 



XV- 10 



