What is another word for spark-gap transmitter?
Pronunciation: [spˈɑːkɡˈap tɹansmˈɪtə] (IPA) 
A spark-gap transmitter, also known as a spark transmitter or an arc transmitter, is an early kind of radio transmitter that used an electric spark to generate radio waves. It was used extensively in the early 20th century before being replaced by vacuum-tube technology. Other synonyms include spark radio, spark oscillator, spark oscillator transmitter, spark coil transmitter, Tesla coil transmitter, and high-frequency spark transmitter. Although these older technologies are no longer in use, they paved the way for modern communication technologies and played a significant role in the development of radio. Today, we continue to benefit from the legacy of these early radio pioneers.
