radiotelegraph

Radiotelegraph is a method of wireless communication that uses radio waves to transmit text by means of Morse code. Unlike radiotelephony, which carries voice, radiotelegraph conveys information by on-off signaling of a transmitter, interpreted by a receiver's telegraph sounder or display.

Developed in the late 19th century, radiotelegraph built on the Morse code system developed by Samuel Morse. Early experimental work by various researchers culminated in practical systems by Guglielmo Marconi and others. By the first decades of the 20th century, radiotelegraphy enabled long-distance, non-wired communications, including transatlantic links and shipboard messaging. Spark-gap transmitters dominated early implementations, producing a broad, noisy signal that required specialized receivers; later, continuous-wave transmitters with keying reduced bandwidth and improved reliability.

Typical equipment includes a radio transmitter, a telegraph key for manual on/off control, a modulator (or simple keying circuit), an antenna system, and a receiver with a detector and sounder or code printer. The operator sends Morse code by short and long on-signal elements; the receiver converts radio energy into audible tones or printed characters. Methods evolved to include radioteletype (RTTY) and other code modes, using standardized character sets.

Today, radiotelegraph is largely superseded by radiotelephony and data communications, but is still used by amateur radio operators and in certain maritime and military contexts. International and national radio regulations—administered by bodies such as the International Telecommunication Union and national authorities—govern licensing, operating procedures, and distress signaling. The Morse code distress signal SOS remains historically associated with radiotelegraph operations, though the use of SOS is deprecated in many systems in favor of digital emergency protocols.