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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



tion is given regarding the loading apparatus and the building-out apparatus. 

 The Type A systems are not included. 



Loading Systems Characteristics 



General: A summary of loading systems characteristics is given in Table 

 XVI, below. Attenuation data are given in Table XVII. 



Compensated Loading Terminations: These loading systems are commonly 

 known as compensated loading by virtue of their use of compensated loading 

 terminations^^ to provide the desired impedance-matching characteristics at 

 about the minimum cost. Over the working carrier-band the impedances of 

 these compensated circuits closely approximate the non-reactive, flat, fre- 

 quency-resistance characteristic of their "corresponding smooth lines"; that 



Table XVI 

 Carrier Loading for Incidental Cables in Open-Wire Carrier Telephone 



Systems 



Notes: * In ordinary quadded cable having 0.062 mf/mi side circuit capacitance, 

 t In special 16 ga. disc insulated cable having 0.025 mf/mi capacitance. 



is to say, the "lumpiness-of -loading" effects on the loaded cable impedance 

 are reduced to tolerable low values over a predetermined frequency-band. 

 By also having the nominal impedance of the loaded cable close to that of 

 the associated open-wire line, satisfactory impedance-matches are obtained 

 up to a much higher fraction of the loading cut-off than is possible with the 

 more simple loading terminations used with the voice-frequency loading. In 

 some carrier loading designs, this impedance-matching band extends up to 

 about 0.75 of the cut-ofif frequency, or a Uttle higher. An extension to still 

 higher frequencies, relative to the cut-off frequency, would tend to result in 

 objectionable *4umpiness-of-loading" attenuation impairments. The com- 

 pensated loading terminations achieve substantial economies in the loading 

 costs by permitting the use of much lower cut-off frequencies than would 

 otherwise be feasible, thus allowing the full-weight coils to be spaced at much 

 longer intervals. 



