Codes and translations

ONE OF the problems which confronted S. F. B. Morse when he undertook to transmit intelligence by means of his electric telegraph was to devise a code suitable to the electric circuit and mechanical apparatus which he had constructed. His solution was the familiar Morse code. The translators for encoding and decoding the electric signals were the telegraph operators. Aleander Graham Bell's telephone avoided the need for translations through the use of conversion devices having simple mathematical relationships between the voice signals and their electrical equivalents; but the discrete, arbitrary relationships which characterize code methods have made their appearance in pulse code modulation recently devised for microwave transmission; the translators in this case are electronic circuits working at tremendous speeds. This article, however, deals not with codes and translators for the transmission of the message itself, but with their use in switching systems for the purpose of setting up telephone connections. Here they have been developed in numerous and varied forms, both for sending telephone numbers or similar information from one central office to another, and also within a central office for signaling from one component of a switching system to another. The forms of the codes and the electrical methods for transmitting them vary with the nature of the information, the form of the apparatus involved, and the character of the signaling channel.