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OCEAN ELECTRONIC NAVIGATIONAL AIDS 



Figure 2-11 — Weatherproof housing of a modern radio direction finder loop antenna 



mounted above deck. 



As the diagram indicates, the minimum is well-defined, and the maximum 

 is not; that is, the strength of the signal varies rapidly with movement of the 

 coil near the minimum, but varies slowly with movement near the maximum. 

 For this reason, the minimum is used in observing bearings. Otherwise there 

 would be important advantages in taking bearings on the maximum, in the 

 way of greater audibility and of thus diminishing the effect of interference. 



In a rotatable coil of practicable size the voltage induced by a radio signal 

 is very small. For the employment of such small coils for radio direction 

 finding purposes it is essential that there be great amplification. 



The radio direction finder should preferably be installed in a position easily 

 accessible to the ship's navigator. The navigator desiring to take a radio 

 bearing simply closes a switch, manipulates a single adjustment until the 

 characteristic signal of the desired rediobeacon is heard, rotates the radio 

 direction-finder loop until the sound becomes a minimum or is inaudible, 

 and then reads the radio bearing. No knowledge of radiotelegraphy is 

 necessary on the part of the navigator. In addition to the desirability of 

 locating the direction-finding equipment at a convenient location, easily 



