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BELL SYSTEM TECHNICAL JOURNAL 



distant listener can set his receiver so that a normal level should be ob- 

 tained for a much larger proportion of the time as the number of sta- 

 tions is increased. As an example, let us consider the proportion of the 

 time that the level of the received program should lie between the limits 

 of 25 and 50 per cent of the maximum signal ; for one station it should be 

 but 17.5 per cent while for two stations it should be 32.5 per cent, for 

 three 45 per cent, and for five 55 per cent of the total time. A further 

 development of the probability integral given above has shown that not 

 only should the proportion of the time that a normal program is re- 

 ceived increase, but that the instantaneous rate of fading should also de- 



-15 

 2 4 



1.6 



5_ 



15 1.2 



50 

 100 



100 

 50 



no 

 woe 



F"ig. 10 — Smoothed curves of field strength vs. distance for stations WOC and 

 WHO, /c = 1000 kc and the envelope of resultant carrier variations for £woc 

 ± £WHO. 



crease as the number of transmitting stations is increased. This is 

 important because the sensitory reaction to fading, within ordinary 

 limits, apparently depends more upon the rate of change of program 

 level than it does upon the absolute total volume change. Since the 

 same arguments apply equally well to each of the individual fre- 

 quencies comprising the side bands, it can be seen that the general 



