d. Susceptibility to Tilt and Polarization Errors 



The system is susceptible to tilt error when multiple antennas are used. 

 The system is also susceptible to horizontal polarization, but this problem may 

 be minimized by using vertical polarization. The Adcock antenna system is 

 widely used to reduce the effects of horizontal polarization, although it is large 

 for shipboard installation. 



e. Susceptibility to Propagation Disturbances 



The system, is not susceptible to propagation disturbances in the pure 

 ground-wave region but is highly susceptible in the sky-wave region. 



f . Susceptibility to Atmospheric Noise 



The system operation is degraded by noise, both man-made and static; 

 thus greater field strengths are required for satisfactory operation. The gen- 

 erally accepted signal strength levels are 70 |-iv/M in noise zones under grade 4 

 and 120 |av/M in noise zones of grade 4 and above. 



REFERENCES 



1. Radio Direction Finding, Special Publication 39, International Hydrographic 

 Bureau, Monaco. 



2. P. C. Sandretto, Electronic Avigation Engineering, IT&T, 67 Broad St., 

 New York, 1958. 



48 



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