duplicated at several points. The chief advantage of this system is that it can be 

 designed so that heterodyning, phase comparison, and distance measurement 

 are all performed at shore stations. The tracked object then requires a mini- 

 mum of equipment, namely a small cw transmitter. For certain applications 

 involving, say, expendable transmitters in buoys, the Type E system can prove 

 quite practical. It is interesting to note that this form of Raydist was used for 

 tracking the first satellites. 



e. Other Systems 



A number of other hyperbolic systems are in limited use, although 

 they are being gradually superseded by the distance-measuring forms. Chief 

 among these is the Type N Raydist, which is completely nonsaturable and finds 

 application where the number of simultaneous users exceeds the capabilities of 

 a DM system. The largest single Type N installation is a network covering the 

 coastal waters of the Gulf of Mexico and used largely for offshore oil exploration. 



3. RANGE AND ACCURACY 



Because of the circular coordinates involved, DM Raydist has substan- 

 tially greater potential for accurate position fixes than do the hyperbolic systems. 

 DM Raydist is more accurate because lane width remains constant with increas- 

 ing range in a circular system, while increasing very rapidly with range in 

 hyperbolic coordinate systems. In addition, the angle of intersection of hyper- 

 bolic coordinate nets increases much more rapidly with range, so that two- 

 dimensional fixes are subject to larger errors. Figure V-10 compares the 

 accuracy of a circular and a hyperbolic system on the basis of these geometric 

 considerations alone. It should be noted that other errors such as propagation 

 velocity and ionospheric effects would also be greater in hyperbolic systems than 

 in the distance-measuring system. 



The frequencies (1.6-5 mc) employed by Raydist provide a lane width 

 equivalent to a one-cycle change in phase. This is equivalent to distances of 

 30 and 100 meters. Since the phase meter can be read to 0.01 lane, readability 

 of Raydist systems is 1/3 - 1 meter in the DM forms, and 1/3 - 1 meter difference 

 in distance with the hyperbolic types. 



Other accuracy considerations include the care with which shore stations 

 are positioned and the system calibration. Experience has shown that accuracies 

 of 1 : 5000 with a probable error of the order of 3 meters can be normally ex- 

 pected, and that accuracies to within 1 meter are achievable. 



129 



arthur ai.ltttlfjnr. 



