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BELL SYSTEM TECHNICAL JOURNAL 



is first, an existiiiii toll telepluMio jilant, which imist be utilized to the 

 maxitmnn ad\;uita.s;e. Also, distances between toll offices or toll 

 centers \ar\-, and particularh- the number of circuits required between 

 given [oW centers varies ovcv a wide range. It follows, therefore, 

 that there is no one type of construction or method which can be 

 economically utilized in all situations. Figure 5. for example, showing 

 a poW line carrying open-wire circuits ami circuits in cable, illustrates 

 some oi our present methods. 



The high-freiiuency broad-band tiansmission dexelopment is being 

 proposed foi three uses: (H for applicatiiMi on telephone toll cables 

 alreadx' in cxistcme. or on future toll cables of \er>- similar t>'pe of 



Fig. 5 — A t\ pii-.il polo lino carr\ ins; both opon wire and cablo. 



consnuciion: {2^ tor an extension to higher frequencies on open-wire 

 telephone circuits, sit as to secure more telephone channels on a 

 given pair; (^v^'i for applicatii>n to new t\-pes of conductors capable of 

 transmitting a \-er>' wide frequency band, such as the "coaxial" 

 ciMiductor. nmv being tried experimentally. 



1 need hardly point out to you that as the frequency of transmission 

 is raised, the attenuation or line loss is greatly increased. This is due 

 more particulaiK- to two factors: an increase in series resistance due 

 to skin ettect. and an increase in shunt conductance due to increased 

 dielectric losses. As the frequenc>- increases, the currents transmitted 

 tend moie and nune to a\oid tlie inner paits of the conductor and lo 



