On the Transmission Capacity of the “Ether” and Wire in Electrocommunications
Vadim A. Kotelnikov · Birkhäuser Boston eBooks · 2001
To broadcast a program by radio or by wire one needs not a single frequency but a whole range of frequencies. Because of this only a limited number of radio stations (which broadcast different programs) may work simultaneously. It is also possible to transmit simultaneously no more than a limited number of programs by one pair of wires because it is impossible for the frequency band of a program to overlap with the frequency band of another program. Such overlapping may cause mutual interferences.