480 



BELL SYSTEM TECHNICAL JOURNAL 



It was desired to equalize the attenuation over a frequency range 

 from zero to 4500 cycles per second and improve the time-of-phase- 

 transmission at the lower frequencies. Computations for this 50-mile 

 cable circuit gave values of attenuation (a in T.U.) and time-of-phase- 

 transmission (b/lTf) as shown in Fig. 15. These circuit characteristics 

 suggested the use of two different networks in tandem shown separately 

 in Fig. 14, one equalizing principally at the lower frequencies, the 

 other at the higher frequencies of the required range. 



Low-Trequency Disiortiorv Correcting Neitvork 



n, 



-o^VVWo— '-0 



Hz' 



:n/i 



L, 



lU 



I 



High-Freguency ditenuaUon Equalizer 



n, 



O-J — oAWW 



Fig. 14 — Distortion correcting networks for program transmission circuit. 



The low-frequency correcting network, shown as the upper section 

 in Fig. 14, is of the symmetrical unbalanced bridged-T (la) type and was 

 transformed from Network 7, Appendix IV. In the design of the 

 latter the attenuation data corresponding to (8) were 



