WIDE BAND TRANSMISSION OVER BALANCED CIRCUITS 7 



balanced to ground with the balanced pairs. The excellence of balance 

 required, of course, depends on the extent to which balance is relied on 

 to reduce the required thickness of sheath. In view of the fact that 

 very thin sheaths are impracticable for mechanical reasons it appears 

 probable that only very modest requirements as to balance need be 

 imposed on the design of these transformers. 



To provide several circuits in new cables for meeting wide-band 

 television needs, another method may be considered, that is, to provide 

 balanced pairs considerably larger in size than ordinary pairs and with 

 the rubber disc form of construction, or other form giving low dielectric 

 losses, but with no shields at all around the individual pairs. Shielding 

 from outside disturbances would be adequately provided by the outside 

 lead sheath of the cable. Crosstalk between different pairs would be 

 the principal concern. If all of the high-frequency pairs were to be 

 used for television transmission, the crosstalk requirements, as already 

 mentioned, would not be severe, so that by careful design the crosstalk 

 could readily be kept within proper bounds — of course, restricting 

 transmission of all wide-frequency bands to a single direction within a 

 single sheath. Such high-frequency balanced pairs might prove suit- 

 able for telephone message circuits also. If not, the high-frequency 

 pairs would be restricted to television only, and other pairs, worked at 

 lower frequencies, would be provided for telephone message service. 



Summary 



It appears feasible under certain conditions to transmit continuous 

 frequency ranges of 1,000,000 cycles or more over conductors in the 

 existing telephone plant. This may some day prove very important, 

 particularly if the art of television develops to the point of calling for 

 such wide frequency range circuits to carry television impulses around 

 the country as sound programs are now carried. 



For new construction, the balanced type of circuit, as well as the 

 unbalanced coaxial circuit, offers many interesting possibilities. 



