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THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 



Examples of attempts to sjnithcsize some more complicated frec{uency 

 sweep patterns, taken on the night of Angust 2, 1949, are shown in 

 Fig. 9. Four components were reciuired in each case, with the path 

 differences and delays being summarized in Table I. Although the pic- 

 tures all appear very different, in general major changes were required 

 only in component Xo. 2 to go from one pattern from the next, as Table I 

 shows. All the remaining components had to be very carefully trimmed 

 in both amplitude and delay to get good synthesis (especially in the case 

 of Fig. 9(d), but these changes were relatively small. 



CONCLUDING REMARKS 



The special experiments just described have led to the conclusion, 

 expressed earlier, that the severe fading observed on the two test paths 

 is the result of multiple-path transmission in which several components 

 may be involved. These components may arrive at the receiver at various 

 angles up to three quarters of a degree above the normal daytime angle- 

 of-arri\'al and, in the case of abnormal water reflection on the Murray 

 Hill path, as much as 0.8 degree below the normal angle. The path 

 differences among these components may \'ary from a fraction of a foot 

 to about ten feet. The long-delaj^ components are usually small in ampli- 

 tude. 



In all cases where observations were made during periods of excep- 

 tionally high signal levels, say 10 to 15 decibels above free space level, 

 the frequency-sweep patterns were substantially flat, suggesting a focus- 

 sing or trapping phenomenon. The frecjuencj'-sweep patterns were also 

 flat on those nights when the signal excursions were only a few decibels 

 above and below the normal daytime level. However, the severe fades 



Table I 



