OCEAN ELECTRONIC NAVIGATIONAL AIDS 



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Figure 2-10. — A typical marker radiobeacou uu a lighted buoy. 



The method of radio direction finding is based on the directive properties 

 of the so-called coil antenna when used for the reception of radio signals. 

 The radio direction finder includes a coil antenna, and operates on the prin- 

 ciple that the amount of electromotive force induced in the vertical loop of 

 wire by an arriving electromagnetic wave depends on the angle between the 

 plane of the loop and the wave front. When the plane of the coil is parallel 

 to the direction of the sending station, the intensity of the signal will be a 

 maximum. As the coil is rotated, the intensity of the signal diminishes until 

 a minimum is reached when the plane of the coil comes to a position at right 

 angles to the line of direction of the signal. The directional characteristic of 

 a coil antenna is illustrated by the diagram in figure 2-12 where the distance 

 from the center of the coil to any point in the circumference of the circles 

 is proportional to the strength of the signal from a direction passing through 

 that point. 



