G. OMEGA VLF NAVIGATION SYSTEM 



1. GENERAL 



The Omega VLF navigation system, undergoing evaluation tests, is 

 an experimental system designed to provide long-range position fixes to ships 

 and aircraft on a 24-hour basis. Omega presently utilizes four experimental 

 stations, located at Summit, Canal Zone; Haiku, Hawaii; Forestport, New York; 

 and Creggion, Wales. The final system, designed to cover the entire globe, 

 will require 8-10 stations. Potential users are surface vessels and all types of 

 aircraft, including those with speeds beyond Mach 1 . 



The assigned frequencies are in the 10-14 kc band now assigned for 

 navigation. Omega is operating at a frequency of 10.2 kc. Hyperbolic lines of 

 position are established by automatic phase -difference measurements of the 

 carrier frequencies at the receiver. The phase -difference values are indicated 

 on dials and strip charts . From these values the navigator determines his 

 line of position from special charts . 



Long base lines are practical at the low frequencies used. If base 

 lines of the order of 3000-5000 miles are used, lines of position will approach 

 parallel lines . By using three stations with base lines at near right angles, all 

 lines of position in the coverage area cross at near 90°, the optimum crossing 

 angle, giving the smallest fix error. 



Coarse position measurement is not available with the developmental 

 Omega equipment but will be added by the spring of 1965 to two of the trans- 

 mitters now in use. Improved receivers, now under development, will also be 

 available at that time. Position determinations to within 1 mile during daylight 

 hours, 2 miles during evening hours, and 6 miles under worst-case conditions 

 are possible with the present prototype equipment. 



2. DESCRIPTION 



An Omega experimental navigational chain is composed of three sta- 

 tions, a master and two synchronized slaves. At present these stations trans- 

 mit sequentially on a frequency of 10.2 kcps . A pulse length of 1 second (ap- 

 proximately) is being used. TTie transmitted pattern is repeated every 4 

 seconds . The stations are identified at the receiver by the slight difference in 

 pulse length characteristic at each station. After transmission the master 

 station stands by while the other synchronized stations transmit their pulses . 



80 



arthur ai.ltittlf.Ilnr. 



