History of equalization 1860-1980

Operators of the first transatlantic telegraph cable in 1858, and subsequent cables from the mid-1860s, noticed that they had to transmit Morse code dots and dashes very slowly to be understood at the other end.1 This phenomenon, due to smearing out of pulses by the capacitive effects of very long cables, had been predicted by William Thomson (more about him below), and was one of the first instances of the need for equalization of digital signals.