Spark-gap transmitter

A spark-gap transmitter is an obsolete type of <a href="/facts/Transmitter/nFYghtKv">radio transmitter</a> which generates <a href="/facts/Radio_wave/LzrVhgbn">radio waves</a> by means of an <a href="/facts/Electric_spark/bckGww30">electric spark</a>. Spark-gap transmitters were the first type of radio transmitter, and were the main type used during the <a href="/facts/Wireless_telegraphy/g1p5PaPA">wireless telegraphy</a> or "spark" era, the first three decades of <a href="/facts/Radio/XFr909M2">radio</a>, from 1887 to the end of World War I. German physicist <a href="/facts/Heinrich_Hertz/sbL2MSpM">Heinrich Hertz</a> built the first experimental spark-gap transmitters in 1887, with which he proved the existence of radio waves and studied their properties.
A fundamental limitation of spark-gap transmitters is that they generate a series of brief transient pulses of radio waves called <a href="/facts/Damped_wave_(radio_transmission)/hXysf4AP">damped waves</a>; they are unable to produce the <a href="/facts/Continuous_wave/XdKlBpgP">continuous waves</a> used to carry <a href="/facts/Audio_signal/rFSTI9IF">audio</a> (sound) in modern <a href="/facts/AM_broadcasting/oS0rn1lg">AM</a> or <a href="/facts/FM_broadcasting/TpKl3FJv">FM</a> radio transmission. So spark-gap transmitters could not transmit audio, and instead transmitted information by <a href="/facts/Radiotelegraphy/g1p5PaPA">radiotelegraphy</a>; the operator switched the transmitter on and off with a <a href="/facts/Telegraph_key/w3hNQRy1">telegraph key</a>, creating pulses of radio waves to spell out text messages in <a href="/facts/Morse_code/GXwCl1HV">Morse code</a>.
The first practical spark gap transmitters and receivers for radiotelegraphy communication were developed by <a href="/facts/Guglielmo_Marconi/U7HXnDnq">Guglielmo Marconi</a> around 1896. One of the first uses for spark-gap transmitters was on ships, to communicate with shore and broadcast a distress call if the ship was sinking. They played a crucial role in maritime rescues such as the 1912 <a href="/facts/Titanic/loD4esxz">RMS Titanic</a> disaster. After World War I, <a href="/facts/Vacuum_tube_oscillator/6NaXsSzJ">vacuum tube transmitters</a> were developed, which were less expensive and produced continuous waves which had a greater range, produced less interference, and could also carry audio, making spark transmitters obsolete by 1920. The radio signals produced by spark-gap transmitters are electrically "noisy"; they have a wide <a href="/facts/Bandwidth_(signal_processing)/7eMDzfJI">bandwidth</a>, creating <a href="/facts/Radio_frequency_interference/gv3DlKNr">radio frequency interference</a> (RFI) that can disrupt other radio transmissions. This type of radio emission has been prohibited by international law since 1934.

Spark-gap transmitter open-in-new

Spark-gap transmitter