486 BELL SYSTEM TECHNICAL JOURNAL 



whence 



ao = .85529; ai = 6.1045- 10-«; 



hi = 39.906-10-''; &2 = 1.9407- 10"^ 



Then in the lattice structure 



i?n = 223.8 ohms; L12 = 9.668 mh.; 

 Ci3 = .005081 mf.; Ru = 1026.3 ohms. 



Transformation to the bridged-T (la) type, using as in (70) c = 1/ao 

 = 1.1692, gave as the elements of the balanced structure of Fig. 16 



Ri = 256.6 ohms; Ro = 94.20 ohms; 



Ri = 111.9 ohms; Ri = 1609 ohms; 



L5 = 9.668 mh.; Lg = 1.829 mh.; 



C7 = .010162 mf.; Cg = .02686 mf. 



Having equalized the dry weather attenuation over the desired 

 frequency range from 10 to 20,000 cycles per second and improved 

 phase conditions at low frequencies, there remained the problem of total 

 phase correction at the higher frequencies. It was found that the 

 high-frequency attenuation equalizer introduced phase distortion at 

 the higher frequencies which was of the same nature but more than 

 twice as great as that due to the original circuit itself. Letting D be 

 the departure from linearity to the value at 20,000 cycles per second 

 of the total phase due to the circuit and the two networks above, the 

 departures at three important frequencies were 



/i = 5,000~, Di = - .686 radian; 

 /2 = 10,000~, D2 = - 1.053 radians; 

 /3 = 20,000~, Dz = 0. 



A phase characteristic which when combined with these departures 



can give an approximate linear resultant phase in that frequency 



range is that of the composite phase Network 16, Appendix IV, 



containing three parameters. Its phase constant B was therefore 



taken to satisfy at these three frequencies the relation B -\- D = Cf, 



or explicitly 



B = Cf - D. (71) 



The constant C was arbitrarily chosen so that the network became 

 physical and satisfactory results were given at intermediate frequencies 

 also. After a number of trials the final value taken was C = .370- lO"-"*. 



