An improved 6-channel time division multiplex for submarine cable telegraphy

The developments of recent decades have sustained the prediction made in 1890 by Mahan that if a successful transisthmian canal were to be built in Central America, the Caribbean would become a great commercial area and a crossroads of transportation, not only of local and of South American traffic but between Europe and Asia as well.1 The importance of Havana, Cuba, in the day of the sailing ship, seated as it is in a geographical position so favored by winds and ocean currents as to command the only passage to Europe, has not been diminished but enhanced by the prophesized burgeoning trade and intercourse. To meet the communications needs of this market place and the richly cultivated area to which it gives access, the Western Union Telegraph Company operates three submarine telegraph cables between Havana and Key West, Fla., an average distance of 101 nautical miles. The second cable of the three was laid in 1889, almost as if in anticipation of Mahan's observation, and the third was laid in 1917, three years after the completion of the Panama Canal and, seemingly, in confirmation of it. Until recently, these duplex-operated cables were terminated in differentially connected polar relays reflecting the land-line practice of those decades, a condition sustaining 3-channel multiplex operation or a signalling capacity three times that of the earlier Morse circuits.