3 ■ AZIMUTHAL SYSTEMS 



Azimuthal systems (angle measurement systems) do not measure a 

 range but measure an angle only. If the transmitter or the receiver position is 

 known, a hyperbolic line of position can be established . Measurements of angle 

 can be made either from shore stations or from a moving vessel. Thus, the 

 azimuthal system requires a known base line and establishes a fix by measure- 

 ment of two or more angles . This type of system is commonly known as radio 

 direction finding (RDF) . Another class of azimuthal system known as Consol 

 (the U .S. version is known as Consolan) uses a rotating radiation pattern and 

 provides identification signals which permit greater angular resolution than is 

 possible with RDF . 



Of the navigation systems in use, the angle measurement systems are 

 the least complicated but also are the least accurate . The uncertainty of the 

 azimuthal measurement of position is determined by the system geometry, the 

 frequency of operation, the range, and other factors . 



C. SYSTEM METHODS 



1 ■ PULSE -TIME SYSTEMS 



For a pulse -time measurement two transmitters are precisely timed 

 to transmit pulsed energy in a fixed sequence from transmitters located at end 

 points on a base line. The receiver, C, may be located at some undetermined 

 point, as shown in Figure III -3a. If the receiver C were placed nearer trans- 

 mitter A on base line AB it would receive pulse A before receiving pulse B. 

 If it were nearer B it would receive pulse B ahead of pulse A. In practice 

 pulse B is transmitted after pulse A and separated from it with a fixed time 

 delay, to eliminate ambiguity and help identify pulses A and B . A comparison 

 of the time of arrival - - by equalizing amplitudes and matching the received 

 pulses at the receiver C --will locate the receiver on a hyperbola along which, 

 by definition, all points have a certain constant distance -difference from two 

 stations . The hyperbola thus forms a navigational line of position . Another 

 pair of signals utilizing stations A and D could be precisely timed and identified 

 in the same manner to form a second hyperbola intersecting the first at the re- 

 ceiver and fixing the receiver's position. 



2. PHASE MEASUREMENT SYSTEMS 



In the second method of position measurement a continuous wave sig- 

 nal is transmitted simultaneously from stations A and B, as in Figure III -3b. 



15 



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