LOADING FOR ll'J.F.ri lONH CIRCUITS 



259 



l)riniary reciuircnuMUs for niatchini^ impedance are that the nominal 

 impedance and the cut-off frecjuency of the cable loading and of the 

 loaded open wire line should be closely the same. To a first degree 

 of approximation this means that the cable loading sections should 

 have the same total mutual capacitance as the open wire loading 

 sections, which, of course, requires a very much closer spacing. The 

 cable loading system which was standardized for use in association 

 with loaded open wire lines is designated "E-248-154". Its primary 

 electrical characteristics are given in Table XII. Besides meeting 



TABLE XII 



Typical Loading Systems for Toll Entrance and Intermediate Cables 



Note. Cable capacitance is assumed to be 0.062 nf per mile for side circuits, anc 

 0.100 nf per mile for phantoms. 



the impedance requirements for use in association with repeatered 

 open wire lines, it is also very satisfactory with respect to attenuation 

 characteristics. In placing this loading, it is customary to locate 

 the first loading point in the cable at such a distance from the last 

 loading point in the open wire line that the total capacitance of the 

 junction loading section is closely the same as that in the regular 

 open wire loading sections. 



Incidental Cables in Non-Loaded Open Wire Lines. The problem 

 of designing coil kniding for incidental caiiles in non-loaded open 

 wire lines is considerably more complicated than the case above 

 discussed, primarily because it involves an impedance match between 

 a smooth line and a lumpy line. Broadly stated, the first part of the 

 problem is to design a lo^ided cable of such characteristics that its 



