Transatlantic Telegraph Cable - Communication Speeds

Communication Speeds

Initially messages were sent by an operator sending Morse code. The reception was very bad on the 1858 cable, and it took two minutes to transmit just one character (a single letter or a single number), a rate of about 0.1 words per minute. This is despite the use of a highly sensitive mirror galvanometer, a new invention of the time.

The first message on the 1858 cable took over 17 hours to transmit. For the 1866 cable, the methods of cable manufacture, as well as sending messages, had been vastly improved. The 1866 cable could transmit eight words a minute – 80 times faster than the 1858 cable. Heaviside and Mihajlo Idvorski Pupin in later decades understood that the bandwidth of a cable is hindered by an imbalance between capacitive and inductive reactance, which causes a severe dispersion and hence a signal distortion; see Telegrapher's equations. This has to be solved by iron tape or by load coils. It was not until the 20th century that message transmission speeds over transatlantic cables would reach even 120 words per minute. Despite this, London had become the world centre in telecommunications. Eventually, no fewer than eleven cables radiated from Porthcurno Cable Station near Land's End and formed with their Commonwealth links a "live" girdle around the world.