Spark-gap transmitter
The first type of radio transmitter, using electric sparks to generate waves.
A spark-gap transmitter is a now-obsolete kind of radio transmitter that worked by creating an electric spark to produce radio waves. It was the very first type of radio transmitter ever built, and it dominated the early decades of radio—known as the wireless telegraphy or "spark" era—from 1887 through the end of World War I. The German physicist Heinrich Hertz constructed the first experimental versions in 1887, using them to demonstrate that radio waves existed and to explore their characteristics.
A major drawback of spark-gap transmitters is that they only generate short, transient bursts of radio waves known as damped waves. They cannot produce the continuous waves needed to carry sound in modern AM or FM radio. As a result, they could not transmit audio. Instead, they sent information via radiotelegraphy: an operator would turn the transmitter on and off using a telegraph key, creating pulses of radio waves that spelled out text messages in Morse code.
The first practical spark-gap transmitters and receivers for radiotelegraphy communication were developed by Guglielmo Marconi around 1896. One early use was on ships, allowing them to communicate with shore and send distress calls if sinking. These transmitters played a vital role in maritime rescues, including the 1912 RMS Titanic disaster. After World War I, vacuum tube transmitters emerged. They were cheaper, produced continuous waves with greater range and less interference, and could also carry audio, making spark-gap transmitters obsolete by 1920. The signals from spark-gap transmitters are electrically noisy, with a wide bandwidth that creates radio frequency interference capable of disrupting other transmissions. This type of emission has been banned by international law since 1934.
**Theory of operation**
Electromagnetic waves are emitted when electric charges accelerate. Radio waves—electromagnetic waves at radio frequencies—can be generated by time-varying electric currents, where electrons flowing through a conductor suddenly change speed, thereby accelerating.
The first device known to generate radio waves was a charged capacitor discharged through an electric spark across a gap between two conductors. The spark itself does not create the radio waves; it acts as a fast switch that excites resonant radio-frequency oscillating currents in the conductors of the attached circuit.
- First built
- 1887
- Inventor
- Heinrich Hertz
- Primary era of use
- 1887 to end of World War I
- Key developer of practical systems
- Guglielmo Marconi (around 1896)
- Prohibited by international law
- 1934
Lore & Background
Spark-gap transmitters were the first type of radio transmitter, and were the main type used during the wireless telegraphy or 'spark' era, the first three decades of radio, from 1887 to the end of World War I. German physicist Heinrich Hertz built the first experimental spark-gap transmitters in 1887, with which he proved the existence of radio waves and studied their properties. The first practical spark gap transmitters and receivers for radiotelegraphy communication were developed by Guglielmo Marconi 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 RMS Titanic disaster.
Reader's Guide
A fundamental limitation of spark-gap transmitters is that they generate a series of brief transient pulses of radio waves called damped waves; they are unable to produce the continuous waves used to carry audio in modern AM or FM radio transmission. So spark-gap transmitters could not transmit audio, and instead transmitted information by radiotelegraphy; the operator switched the transmitter on and off with a telegraph key, creating pulses of radio waves to spell out text messages in Morse code. After World War I, vacuum tube transmitters 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 bandwidth, creating radio frequency interference (RFI) that can disrupt other radio transmissions. This type of radio emission has been prohibited by international law since 1934.
Did You Know?
- Spark-gap transmitters could not transmit audio; they only sent Morse code by switching the transmitter on and off with a telegraph key.
- The spark itself does not produce the radio waves; it serves as a fast-acting switch to excite resonant radio-frequency oscillating currents in the attached circuit.
- The radio signals from spark-gap transmitters have a wide bandwidth, creating radio frequency interference that has been prohibited by international law since 1934.
More in Radio Electronics, Part 3 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced