(5) Ambiguities: modern equipment utilizes antenna generating a 

 cardioid field pattern with one maxima and one minima so that no 

 ambiguity exists. 



(6) Limitations on number of users: none. 



(7) Frequency allocation: cw carrier in band between 100 kc and 

 1750 kc. Marine RDF stations are allocated frequencies in the 

 405 - 415 kc band, the standard frequency being 410 kc. UoS. 

 Coast Guard radio beacons operate in the frequency range of 

 285 - 325 kc. 



(8) Fail-safe feature: system is not fail-safe, although it has fail- 

 safe features. 



(9) Coverage: the coverage of a RDF is dependent upon: 



(a) radiated power 



(b) noise level 



(c) receiver bandwidth 



(d) terrain 



(e) magnitude of interfering sky wave. 



b. S/N Ratio 



A S/N level of 6 db is considered adequate for steady readings. A 

 1.2/1 ratio will give values that can be averaged. A daytime LOP range of 

 300 - 600 miles using the ground wave is typical for a 200 -kc beacon radiating 

 1 kw of power. This range will decrease to about 350 miles at frequencies of 

 the order of 1500 kc (considering over-water transmission). 



c . Ground or Sky Wave 



Beacons operate most reliably on ground wave. The sky wave produces 

 stronger signal levels at greater distances than the surface wave, especially 

 during the hours between sunset and sunrise and at the lower frequencies used 

 during the day. Sky-wave field intensity is subject to diurnal, seasonal, and 

 ionospheric variations. These effects decrease the reliability of the fix when 

 using the sky wave. 



47 



arthttr Zn.ltittlfjnr. 



