si.i.iciiri iiKcriis .txn si.iin i\ 1 1 i,-i r.Ri sen 271 



lakfii .IS thf iiii(l-frt'<iiit'tu'\' Wm of llu' h.md wliicli iii.iy In- (li'l'mcd 

 fitluT .IS (wi+w.) 2 or as wlu^^. C"onso(nu'iitK- 



It Jo I Z(lw) ,- 



l-'nim (,!•) it follows tli.il tlir iikmii sciu.irc ruiiHiil I', due to r.iiidom 

 intfiffrfiui', is nunlu up of two factors: one R {w,,,) which is propor- 

 tion. il to thecnerny level of the interference spectrum at mid-frequency 

 u)« '2 k: anil, second, the intej^ral 



which is independent of the ch.iracter antl intensity- of the interference. 

 Thus 



l- = pR(icJ. (11) 



I'ornuil.i (11) is of considerable practical importance, because by its 

 aid the spectral energy level R (w) can be determined, once /- is 

 e.\i)erimentally measured and the frequency characteristics of the 

 receiving network specified or measured. Il is approximate, as dis- 

 cussed above, but can be made as accurate as desired by emplo\ing 

 a sufficiently sharply selective network. 



The formula for ihe Jigti re of merit of a selective circuit 'witli respect 

 to random interference is constructed as follows: 



Let the signaling energy be supposed to be spread continuously 

 and uniformly over the frequency interval corresponding tooji^co^wj. 

 Then the mean square signal current is given by 



£- /•W5 d u 





I Ziiw) 1^ 

 or, rather, on the basis of the same transmitted energy to 



^rT7?7Tr=^^-^- (^2) 



£» 



7r(a)2 — 0)1 



The ratio of the mean square currents, due to signal and to interfer- 

 ence, is 



^^ ' " (13) 



R{li}„) 0)2 — 0)1 p' 



E- 

 The first factor "- depends onlv f)n the signal anfl interference 



A(o)b,) 



energy levels, and does not involve the properties of the network. The 

 second factor depends only on the network and measures the 



