The telephone channel capacity of transmission lines

The attenuation of transmission lines used for telephone transmission varies very nearly as the square root of frequency when dielectric loss is small and conductor resistance is controlled by skin effect. In this paper the maximum number of telephone channels which can be obtained on such a line using a.m.-f.d.m., f.m.-f.d.m., and p.c.m.- t.d.m. is calculated as a function of line attenuation at a reference frequency, transmitted power level, and signal/noise ratio. At moderate and high transmitting levels s.s.b.-a.m. usually permits the greatest number of channels to be derived.