3. ACCURACY 



Little data is available on the accuracy of non-directional beacons. A 

 value widely used for o is ± 3° when within the limits of ground-wave range. This 

 indicates a 6° LOP error band 95% of the time. At distances less than 80 miles 

 errors in LOP due to night effects are small, and errors of 2 - 3° can be expected. 



Night effect occurs because a horizontal component of radio energy is 

 generated when energy is reflected from the ionosphere and interferes with 

 energy transmitted in the ground plane. The horizontal component results from 

 the rotation of the vertical plane of polarization during propagation through the 

 ionosphere. 



The effects of terrain- -reflections off mountains and irregularities in 

 the coast line- -decrease the accuracy by the ratio of direct to reflected energy. 

 Refraction can take place and produce LOP errors which may exceed 5 ° when 

 energy propagated crosses a sea-land mass obliquely. 



4. SUMMARY 



a. Type of System 



(1) Azimuthal, measuring angles. 



(2) Base line length: on the order of ratio of antenna loop diameter to rf 

 wave length. LOP are obtained by use of relative bearing and 

 magnetic compass information. 



(3) Type of modulation: modulation of the carrier is used for station 

 identification purposes. 



(4) Presentation: 



(a) Visual or aural: presentation is visual for navigation, aural 

 for identification. 



(b) Automatic or manual: fix information requires manual tuning 

 and plotting. Presentation is continuous. 



(c) Time to establish position: approximately 2 minutes including 

 plot time. Time to establish fix depends upon difference in 

 angle between RDF needle position when resonance is first 

 obtained and the final needle position when the needle is at 

 rest on the bearing. 



46 



Arthur BMttlcMc. 



