Frequency-Shift Telegraphy
Frequency-Shift Telegraphy
a method of transmitting electric telegraph signals over communications lines by means of alternating currents. It converts DC signals formed by telegraph apparatus into AC signals, which are then transmitted over the line (cable, radio-relay link, or the like). The channel equipment (seeMULTICHANNEL COMMUNICATION) produces from one to 24 or more channels within one standard voice-frequency telegraph channel (0.3–3.4 kilohertz). The signal in each channel of the system is transmitted on its own carrier frequency, usually by means of frequency modulation; amplitude and phase modulation are also sometimes used.