b. Performance Potential 



(1) Ground-Based HF DF Techniques 



The technique for HF radio direction finding is 

 highly developed and the United States currently operates several HF DF 

 networks. A DF network consists of two or more DF stations, which are 

 tied together via a communications system. The exchange of signal fre- 

 quency, and signal bearing information between the DF stations, allows 

 the location of the signal source to be determined by triangulation. 

 The sophistication of the DF network ranges from one-man, manually oper- 

 ated, portable DF stations to highly automated, fixed site, DF stations 

 each costing several millions of dollars. The size of the DF station 

 is determined primarily by the work load (i.e., number of signal fre- 

 quencies that must be monitored) and to a lesser extent by the DF accuracy 

 required. Generally one large antenna, such as a 1000-ft-diameter 

 Wullenweber array, is used. This one antenna has the capability to ser- 

 vice many intercept and DF operators. 



Historically, HF DF has been used for direction 

 finding related to the navigation of aircraft and surface ships, and 

 to the location of aircraft or surface ships in an emergency situation. 

 Currently, HF DF is largely used for monitoring and surveillance. For 

 example, the FCC operates an HF DF network in the United States to 

 locate illegal radio transmitters and sources of radio interference to 

 authorized radio facilities. DoD operates several HF DF networks for 

 surveillance and intelligence data collection. HF DF is seldom used 

 for navigation because most navigation systems have greater position 

 location accuracy. 



Federal Communication Commission. 



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