The phase of signal B is usually "phase -locked" to signal A. Thus, the phase 

 difference of signals A and B at receiver C is a function of the position of the 

 receiver with respect to each transmitter. For example, if line XY is the right 

 bisector of the base line AB, it follows that at any point on line XY the signals from 

 transmitters A and B will be in phase and a phase meter will read zero, as the 

 signals will have traveled equal distances, assuming their velocity to be constant. 

 Should receiver C be moved nearer transmitter A by a distance corresponding 

 to one -half wave length of the transmitting frequency, the two signals from A 

 and B would be 180 degrees out of phase and would have traversed one lane width . 

 A second station, D, also phase -locked to station A operates in like manner and 

 generates a second set of hyperbolic lines of position. The receiving and phase 

 comparison devices are duplicated to work with the two sets of coordinates, and 

 the observer fixes his position at any point in time by transferring the readings 

 of the phase meters to a chart on which numbered lanes of the two patterns are 

 printed. The proper reading of position is dependent upon initially setting the 

 two phase meter dials and recording the reading when the receiver is at a known 

 geographical position with respect to points A and B . 



3 . ANGLE MEASUREMENT 



For this method only an angle is required to establish a line of position. 

 Range is not measured. Two or more lines of position can establish a navigational 

 fix. 



Figure III -4 shows the geometry of the angle measurement system. 



A B 



•^ -P 



/c 



FIGURE III -4 ANGLE MEASURING SYSTEM GEOMETRY 



In this figure, A and B represent the known locations and C represents the po- 

 sition to be determined by angle measurement. AC and BC are the lines of posi- 

 tion. The position of C may be fixed by transmitting from C and determining 



17 



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