AbstractTheOMEGA NavigationSystem, consisting of eight transmitting stations operating in the 10–14 kHz frequency spectrum, is scheduled to be completed by the end of 1974. When fully operational, navigation using relatively simple equipment will be possible at essentially any point on the globe. To improve positioning accuracy, a technique of differential OMEGA can be employed to remove propagation errors introduced by diurnal height shifts of the ionosphere and other causes.This paper discusses some possible limitations to the differential technique and presents a sample of data obtained during an experiment performed during the period January to April 1972 for the U. S. Coast Guard. Also discussed are the effects on accuracy of power line harmonic interference on short term phase stabilit