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BELL SYSTEM TECHNICAL JOURNAL 



ditions of strong signals, a simple antenna appears to perform as well 

 as one considerably more elaborate and expensive. 



Fig. 1 will assist in comparing the relative importance of set noise 

 and static interference. The figure is not intended to be strictly accur- 



HALF WAVE VERTICAL ANTENNA 



ANTENNA DISCRIMINATION REQUIRED 



AVERAGE STATIC 



30 M. APPROX. 

 WAVE LENGTH 



Fig. 1 — Relative distribution of static and set noise with wave-length. 



ate as to numerical values but will convey the idea of the principles 

 involved. There is plotted as a function of wave-length, for an arbi- 

 trary location and season, the average static voltage level delivered to 

 the first tube of a receiver by a half-wave, vertical antenna through its 

 coupling circuits. Likewise, we have plotted the circuit noise delivered 

 to this same tube as a function of wave-length. The fact that these 

 curves intersect is of importance. 



At wave-lengths considerably below the point of intersection, a weak 

 signal falls into the level of the set noise. Increased signal output from 

 the antenna is desirable to override this noise. It is evident that static 

 reduction through directional discrimination is of little use in this 

 region, therefore an antenna having directional properties but possess- 

 ing no marked gain in output over a simple nondirectional antenna has 

 no merit. At wave-lengths considerably above the point of intersec- 

 tion, static reduction through directivity is of utmost importance, while 

 a gain in antenna output would be of little value if it meant a gain in 

 static as well as in signal. It is interesting to observe, however, that a 

 sufficient reduction of static through directivity would lower the whole 

 static curve until it lay below the set noise curve. Such being the case, 

 signal gain would again be required. 



