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BELL SYSTEM TECHNICAL JOURNAL 



ing coils and in the loading systems, in order to meet new or changing 

 requirements in the rapidly advancing communication art. The more 

 important of these improvements are listed below and will be discussed 

 in the sequence noted: 



I. Phantom droup Loading 



II. Loading for Repeatered Circuits 



III. Incidental Cables in Open Wire Lines 



IV. Cross-Talk 



V. Telegraphy over Loaded Telephone Circuits 



VI. Loading for Exchange Area Cables 



VII. Submarine Cables 



As a basis for the discussion of the characteristics of commercial 

 loading systems and the various developments which have been made, 

 the elementary theory of loaded lines and a review of the first loading 

 standards will be given. Those interested in the exact mathematical 

 theory are referred to more complete discussions which may be found 

 in the bibliography appended hereto. 



Theory^. It is convenient to discuss the coil loaded line in terms of 

 its corresponding smooth line, a hypothetical line in which the con- 

 stants of the inductance coils are assumed to be distributed uniformly 

 along the line. 



Table I gives simplified formulas which define the important line 

 characteristics in terms of the primary line constants, the formulas 



TABLE I 



Approximate Line Formulas 



Line 

 Characteristics 



Uniform Line 

 Having Zero 

 Inductance 



LTniform Line Having 

 Distributed Inductance 



a, Attenuation 

 constant 



W, velocity of 

 wave propa- 

 gation 



Zo, characteristic 

 impedance 



I R IpRC _ R_ I C 

 ^IZp'y 2 ~ 2 ^ L 



\ 2Lp ■\ RC \ CL 



(1) 



(2) 

 (3) 



In the above, a is the real part of the propagation constant; and W = p/0, in 

 which />=27r/(/ = frequency) and /3 is the wave length constant; /. e., the imaginary 

 part of the propagation constant. The formulas assume the leakage conductance G 

 to be negligibly small; and in the case of the line with inductance, that R is small with 

 reference to p L; R, L, and C being the line resistance, inductance, and capacitance 

 per unit length. 



^This section on Thcjry contains a small amount of discussion not included in the 

 paper as presented. 



