Radio telegraph

Wireless telegraphy is the transmission of electric telegraphy signals without wires (wirelessly). It is now used as a historical term for early radio telegraphy systems which communicated with radio waves, although when the term originated in the late 19th century it was also used for a variety of other experimental techniques for communicating telegraphically without wires, such as photoelectric and induction telegraphy.

Wireless telegraphy came to mean Morse code transmitted by radio waves (electromagnetic waves), initially called "Hertzian waves", discovered by Heinrich Hertz in 1886. The primitive spark radio transmitters used until World War 1 could not transmit audio (sound). Instead they transmitted information by telegraphy: the operator would tap on a switch called a telegraph key turning the transmitter on and off, producing different length pulses of radio waves spelling out text messages in Morse code. The code sounded like musical "beeps" in the earphone of the receiver. The receiving radio operator would translate the beeps back into text.

The first practical wireless telegraphy transmitters and receivers were developed by Guglielmo Marconi beginning in 1895. By 1910 communication by Hertzian waves was universally referred to as "radio", and the term wireless telegraphy has been largely replaced by the more modern term "radiotelegraphy". The transmission of sound (radiotelephony) began to displace wireless telegraphy by the 1920s for many applications, making possible radio broadcasting. Wireless telegraphy continued to be used for private person-to-person business, governmental, and military communication, such as telegrams and diplomatic communications, and evolved into radioteletype networks. Continuous wave (CW) radiotelegraphy is regulated by the International Telecommunication Union (ITU) as emission type A1A.

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