OCEAN ELECTRONIC NAVIGATIONAL AIDS 3 



A vibrating quartz crystal is the balance wheel, and electrical circuits known 

 as "dividers" or "counters" take the place of gear wheels. 



Installation of the receiving equipment is quite simple and can be performed 

 in a few hours' time. Actually, installation merely requires simple mechani- 

 cal mounting of the equipment to the deck or bulkhead, erection of an ordinary 

 radio receiving-type vertical antenna, and plugging in the power cord to the 

 local electrical power source. 



OPERATING RANGE AND ACCURACY 



Three fundamental characteristics of Loran are of particular importance 

 to navigators using the system. These qualities are the following: 



(1) Practicability of Loran operation over longer distances than is pos- 

 sible with older types of radio navigational aids. 



LINE OF POSI- 

 TION DETER- 

 MINED FROM . 

 "B" READING 



LINE OF POSI- 

 TION DETER- 

 MINED FROM 

 "A" READING 



Figure 1-2. 



Navigator aboard Loran-equipped ship at S establislies "fix" by determining two lines of 



position, A and B by Loran measurements. 

 Line of position A is found by measuring the time difference between signals received 



from transmitting stations Ai and Ag. 

 Line of position B is found by measuring the time difference between signals received 



from transmitting stations Bi and B2. 



The navigators fix is established at the point of intersection of the two lines of position. 



The latitude and longitude of the navigator's position is determined from the Loran data 



by using either the Loran charts or Loran tables. 



:(2) High order of positional accuracy attained. 



(3) Reliability of Loran under all kinds of weather conditions. 



Vessels and aircraft at sea may determine their position by means of Loran 

 both day and night when they are within 750 nautical miles of the transmit- 

 ting stations. This is based on the reception of "ground waves," which 

 travel on the surface of the earth and are the most stable type of radio waves. 

 At night, however, "sky waves" are received which are radio waves that travel 

 outward from the transmitter until they "bounce" or are reflected from a 

 region of the upper atmosphere known as the "ionosphere" and reach the 

 navigator after reflection (fig. 1-4). The use of "sky waves" extends the 

 range of Loran service at night up to a distance of 1,400 nautical miles from 

 the transmitting stations. However, the positional data obtained by using 

 "sky waves" Loran signals is somewhat less accurate than the information 



