What type of transmitter represents the earliest form of radio communication?

The earliest form of radio communication is represented by the continuous wave transmitter. This technology, developed in the late 19th century, utilizes a simple on-off transmission of radio waves to convey information, primarily through Morse code. Continuous wave transmission sends a single frequency without varying the amplitude or frequency, which was revolutionary at the time for long-distance communication.

Continuous wave transmitters were pivotal in establishing fundamental communication practices, laying the groundwork for more complex modulation techniques that followed, such as amplitude modulation (AM) and frequency modulation (FM). By using a stable frequency, the continuous wave method allowed for clearer reception, which was essential for early amateur radio operators and maritime communication. The simplicity and effectiveness of this method highlight its significance as the foundation of radio technology.