D. RAYDIST 



1. GENERAL 



Raydist is the generic name of a family of radio distance-measuring 

 and navigation systems produced commercially by Hastings -Raydist, Inc. , 

 Hampton, Virginia. These systems are used extensively by the U. So Coast 

 and Geodetic Survey and by a number of commercial organizations and foreign 

 governments. 



All forms of Raydist operate on the same basic principle. Two cw 

 transmitters are located on a base line and separated by a distance of up to 100 

 miles. They are operated at frequencies in the 1.6-5 mc range, the two trans- 

 missions differing by about 400 cps. The 400 cps beat note is obtained at each 

 station and retransmitted to some convenient location where phase comparison 

 is performed, yielding interstation distance. The frequency range used permits 

 small efficient transmitters and operation to beyond line -of- sight. 



Several geometric configurations are possible, depending upon the 

 position of the stations, and include hyperbolic and elliptic coordinates, angle 

 measurements, and circular or direct distance measurements. Because of the 

 vast superiority of direct distance measurement, this system (DM) is replacing 

 the others in all but a limited number of applications. It is illustrated in 

 Figure V-9. Its major advantages are the requirement for only two stations, 

 the simplified circular charts, and the much higher accuracy and area coverage 

 inherent in the circular geometry. 



All forms of Raydist are entirely automatic in operation, the position 

 data being read directly from the phase meter dial or from the plot of an auto- 

 matic position recorder. Accuracies of one part in 5000 can normally be 

 expected, while one part in 50,000 or better is achievable in certain survey 

 operations . 



2. DESCRIPTION 



a. DM Raydist 



This system was developed for precise two-dimensional tracking of 

 small cw transmitters for purposes of navigation, surveying, or position plotting. 

 It gives the instantaneous position of a mobile transmitter with reference to two 

 fixed receiving stations identified as the red and green stations. Mobile station 

 equipment includes a cw transmitter, and the "Navigator, " consisting of a spe- 

 cial-purpose, dual-frequency receiver and aphase comparison unit (Fig. V-9), 



126 



artbur Zn.'iLtttlcilnr. 



