A spark-gap transmitter produces electromagnetic waves that can be picked up on a receiver tuned to a specific frequency. The development of this technology laid the groundwork for widespread radio communication around the world. Although it is not in wide use today because of its inefficiency and interference problems, some replica transmitters can be seen in museums and similar settings. It is also possible to build a transmitter for experiments and education.
With a spark-gap transmitter, an operator relies on two electrodes separated by a gap. When the operator supplies enough voltage, a spark will develop and spring across the gap, creating a route for the current. This creates an electromagnetic signal which can be transmitted with the use of an antenna. A receiver can pick up the signal, allowing for remote communication between two locations.
This technology relies on the use of tools like Morse code for transmission, as operators cannot send actual voices. Instead, a Morse key can be activated to send intermittent tones, which an operator on the receiving end can decode and translate into words. Early spark-gap transmitter operators developed shorthand in their signaling to quickly send information without having to spell out each word. This shorthand was standardized to avoid confusion, creating an international radio language that allowed people to communicate even when they didn't speak the same tongue.
There are a number of problems with the spark-gap transmitter. It tends to be subject to and can generate interference, and also operates in broadband. This can be a problem when there is fierce competition for available radio frequencies. The technology also transmits across a limited distance, hampered by the antenna, and allows for only crude communication. These issues led inventors to keep working on radio technology, and they eventually developed other modes of communication.
Radio operators began phasing out the spark-gap transmitter in the early 20th century, with a few exceptions for backup units in settings like ships. Numerous nations also agreed to suspend use of this technology, by international treaty, to free up frequencies for other uses. While the spark-gap transmitter was a pioneering invention in wireless telegraphy to enable communication across areas not linked by cable, it was ultimately phased out in favor of safer, more powerful, and more efficient systems. Hobbyists sometimes build replica systems to display the technology, and numerous recordings can be found online to demonstrate what spark-gap transmitters sounded like in operation.