28 



OCEAN ELECTRONIC NAVIGATIONAL AIDS 



-Tli.^ li 



nt at a cla-~ \ i iiliobeacon station, 

 .locks showu at ihu k'ft. 



One of the 



it is convenient to synchronize stations in groups of three, and this grouping 

 and synchronization has been extended to the whole system. Radiobeacons 

 transmit on even frequencies in the band 285 to 325 kilocycles (i. e., 286, 288, 

 290, etc.). 



SIGNAL CHARACTERISTICS 



The radiobeacon is an aid to navigation and is therefore made as con- 

 veniently available to the navigator as practicable. Consistent with this idea, 

 the characteristics assigned to radiobeacon stations in this country have been 

 limited to brief and simple combinations of dashes and dots, corresponding 

 in no case to more than a single International Morse code symbol. They are 

 thus differentiated on the same principle as are lights along the coast, a 

 system to which navigators are accustomed. The entire transmission for any 

 station is a repetition of the assigned signal, without variation. There is a 

 minor exception to this in the case of distance-finding stations. The advan- 

 tage in this arrangement is that whenever a radiobeacon is heard its identity 

 is immediately apparent, even to a navigator who is not a radio operator. 

 There appears to be no diflBculty in differentiating radiobeacon signals from 

 other transmissions, and therefore the use of a common distinguishing letter 

 for all radiobeacons has been considered unessential. 



TYPE OF MARINE RADIOBEACON EMISSION 



All marine radiobeacon stations in the United States emit type A2 signals. 

 This type of emission is obtained by either keying the modulating audio 

 frequency or by the keying of the modulated carrier. 



Radio direction finders have generally been designed so as to be capable 

 of taking bearings on either unmodulated continuous wave or modulated con- 

 tinuous wave signals. 



MARINE RADIOBEACON TONE CHARACTERISTICS 



The audio modulation frequency of 1000 cycles has been adopted in the 

 United States as the standard tone for marine radiobeacons. However, tonal 



