What is the purpose of a corona ball on an HF mobile antenna?

When transmitting on HF, especially with the physically short and highly loaded antennas used in mobile installations, extremely high RF voltages can build up at the very tip of the antenna whip. If the tip is sharp or pointed, these high voltages can easily ionize the surrounding air, creating a visible, hissing electrical arc known as a corona discharge. This discharge wastes transmitter power, creates static interference, and can physically damage or melt the tip of the antenna. A 'corona ball' is a smooth, rounded metal sphere attached to the top of the antenna. Its spherical shape distributes the electrical field over a much larger surface area, effectively preventing the high-voltage RF from arcing into the air.