DISTORTION CORRECTION 485 



From a study of these characteristics and those of certain distortion 

 correcting networks it appeared possible to obtain a base network 

 design for the dry weather condition and supplementary networks for 

 various degrees of wet weather. 



The dry weather network consists of three parts in tandem, a low- 

 frequency distortion correcting network, a high-frequency attenuation 

 equalizer, and a high-frequency phase corrector, which were designed 

 in the order given. The final structures are shown in Fig. 16, the first 

 two being put in the form of balanced bridged-T (la) types. The 

 low-frequency distortion correcting section corresponds to Network 

 \h, Appendix IV, and, while designed to approximately equalize the 

 attenuation at low frequencies, it gave at the same time sufficient 

 phase correction in that frequency range. The attenuation data used 

 were 



/i = 50 ~, Ai = .409 napier; 

 /2 = 500~, Ai = .060 napier; 



from which, where R = 600 ohms, 



Po = 60,307; Qo = 25,217; 



ao = .2145; bi = 4.945-10-='; 



Rn = 257.4 ohms; C12 = 3.056 mf. 



Transformation in the usual manner to the bridged-T (la) type, 

 letting c = 1/ao = 4.662, gave the balanced structure of Fig. 16 in 

 which 



Ri = 64.35 ohms; R2 = 1334 ohms; 



Cs = 6.112 mf.; L4 = 1.100 h. 



The high-frequency attenuation equalizer was derived from Net- 

 work 8, Appendix IV, with this data, which followed formula (8) and 

 allowed for the attenuation of the preceding network. The amount 

 of attenuation at the highest frequency was arbitrarily assumed to be 

 .400 napier. 



/o = 0, Ao = 2.551 napiers; 



/i = 5,000-, ^1 = 2.100 napiers; 



/o = 10,000-, Ao = 1.476 napiers; 



/3 = 20,000-, A3 ^ .400 napier. 



Solution of the linear equations gave 

 P2 = - 53.683 -lO-^; Q2 = 5.0669- 10-«; Qi = 3.7662- 10-i«; 



