DEFERRARI: FIXED-SYSTEM MEASUREMENTS OF TIME-VARYING MULTIPATH 

 AND DOPPLER SPREADING 



algorithms that can track rays incident on the surface all along the 

 propagation path and find those scattered rays which hit the receiver. 

 Thus, multiple scattering along the path can be accounted for. 



The types of ray paths that can be expected in the Florida Straits 

 are shown in the other diagrams on Figure 6. The downward refracting 

 profile leads to rays which are refracted bottom- reflected (RBR) and 

 surface-reflected bottom-reflected (SRBR) . The SRBR rays can be 

 surface scattered (as in the illustration) after any number of specular 

 bounces. This happens to be a ray which reflects specularly twice, 

 then upscatters and reflects specularly as its new angle before reach- 

 ing the receiver. The model does all the bookkeeping for these paths. 



We will now discuss the data. Figure 7 shows CW propagation loss 

 for the 700-mile range between Eleuthera and Bermuda over a 48-hour 

 period; typical multipath deep fades (30 dB or so) are shown with their 

 associated phase shifts. If the fades are very deep the phase shift 

 appear to be 180 degrees. Most of the phase fluctuations are quasi- 

 periodic, varying with the tidal component. 



It's interesting to compare these sorts of fluctuations with what 

 we see at other ranges. Figure 8 compares propagation-loss and phase 

 data for the 700 nautical mile range to Bermuda, the 300-mile range 

 to Eleuthera and the 7-mile range in the Florida Straits. They all 

 have the characteristic dropouts in signal level due to multipath 

 influence. The principal difference between them is that for the 

 longer ranges the fades are more rapid than for the shorter ranges. 

 However, the fades tend to have the same magnitude, typically 15 to 

 30 dB for deep- fading events. The phase has similar characteristics, 

 with smooth variations (showing a strong tidal periodicity in the 

 Eleuthera data) plus a number of rapid shifts of 180 degrees associated 

 with deep fades . 



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