The phase comparison system uses a phase discriminator to compare 

 the phase of the master oscillator with that of each slave station and displays 

 this difference on a goniometer dial in terms of lanes and fractions of lanes . 

 Each of the two goniometers mounted on the receiver panel makes one revolution 

 per lane or phase -difference cycle, and each is capable of driving various other 

 displays. The goniometer has an accuracy of about 1 degree of phase, thus pro- 

 ducing little error due to nonlinearity . The two lane counts are displayed on 

 digital counters accommodating 999.99 lanes. 



The use of an identical frequency of transmission by the master and 

 both slave stations frees the system from differential phase errors due to ther- 

 mal or other causes in the two halves of the phase -comparison circuit. 



With Hi -Fix type A no means of coarse positioning is provided, and 

 the navigator must keep track of lanes with respect to a known starting point. 

 Lane identification can be provided by a system known as Hi -Fix type B . With 

 this system additional receiver -transmitter units are placed at each station, 

 and a second grid is generated. In this manner automatic and continuous lane 

 identification is provided . 



3. ACCURACY 



The Hi -Fix system can generate either a hyperbolic or a circular 

 pattern . The circular coordinate system has the advantage of a constant lane 

 width with increasing range. The lane width of the system is about 250 feet, 

 and the instrument accuracy corresponds to about 0.01 lane. The patterns gen- 

 erated are illustrated in Figure VI-5, where the relative accuracy of the sys- 

 tem using the two patterns is indicated. 



The working range is dependent largely upon the sight and the atmos- 

 pheric noise level. Typical operating distances between Hi -Fix transmitters 

 and receivers are 5-35 miles, but ranges of 100 - 130 miles can be obtained . 



(2) 



With Hi -Fix set up as a h3fperbolic system, one series of tests^ 



indicated system accuracy to be about ±0.05 lane, which is equivalent to be- 

 tween ±10-40 feet. For this case the transmission path was across both land 

 and water. Rather large systematic errors can be expected for this situation 

 where the propagation velocity is dependent upon the electrical conductivity of 

 the terrain and proper corrections are not applied . When these measurements 

 were repeated from the same stations for paths over water, the standard devia- 

 tion for readings was of the order of ±0 .01 - .02 lanes which is equivalent to 

 a positional accuracy of between 2.5 and 7 feet . 



165 



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