Crosstalk and Noise Features of Cable Carrier Telephone System

ROSSTALK and noise are important factors in cable carrier transmission as outlined in the paper "A Carrier Telephone System for Toll Cables" by Messrs. C. W. Green and E. I. Green. Crosstalk and noise limit the number of carrier channels which can be utilized in any one cable, not only by limiting the number of channels which can be placed on a single pair, but by limiting the number of pairs which can be used. Noise also controls the transmission loss which can be permitted between repeaters. Without the crosstalk and noise reduction measures described in this paper, the number of carrier channels per cable would be so few and the spacing between repeaters so short, that the type K carrier system would be impracticable. CROSSTALK To utilize existing toll cables in the Bell System for frequencies up to 60 kilycycles required the solution of many new crosstalk problems because: (1) Crosstalk increases rapidly with the frequency, (2) Nonloaded carrier pairs due to their high speed of propagation are especially suitable for very long distances and hence the crosstalk requirements per unit length are relatively severe, (3) The large gains of the carrier repeaters amplify certain crosstalk currents much more than in the case of voice frequency circuits. Two general effects need to be considered: intelligible crosstalk must be prevented; and, a large number of circuits crosstalking into a particular circuit must not contribute an undue amount of noise. T h e second effect is called babble, since it consists of a multiplicity of unrelated voice sounds which, in the aggregate, are unintelligible.