Systems for Wide-Band Transmission Over Coaxial Lines

TT appears from recent development work t h a t under some conditions it will be economically advantageous to make use of considerably wider frequency ranges for telephone and telegraph transmission than are now in use 112 or than are covered in the recent paper on carrier in cable. 3 Furthermore, the possibilities of television have come into active consideration and it is realized that a band of the order of one million cycles or more in width would be essential for television of reasonably high definition if t h a t art were to come into practical use. 4,6 This paper describes certain apparatus and structures which have been developed to employ such wide frequency ranges. The future commercial application of these systems will depend upon a great many factors, including the demand for additional large groups of communication facilities or of facilities for television. Their practical introduction is, therefore, not immediately contemplated and, in any event, will necessarily be a very gradual process. T Y P E S OF HIGH-FREQUENCY CIRCUITS The existing types of wire circuits can be worked to frequencies of tens of thousands of cycles, as is evidenced by the widespread application of carrier systems to the open-wire telephone plant and by the development of carrier systems for telephone cable circuits. 2,3 Further development may lead to the operation of still higher frequencies over the existing types of plant. However, for protection against external interference these circuits rely upon balance, and as the frequency band is widened, it becomes more and more difficult to maintain a sufficiently high degree of balance.