What is meant by "flat topping" in a single-sideband phone transmission?

"Flat topping" refers to a specific type of severe signal distortion that occurs when an amplifier is driven beyond its linear operating range. On an oscilloscope, the peaks of the radio frequency waveform literally appear clipped off or "flat," rather than forming a smooth, continuous wave. In a single-sideband (SSB) transmitter, this is usually caused by excessive audio drive, such as turning the microphone gain up too high. The amplifier runs out of voltage or current capacity to reproduce the peaks of the signal accurately. Because SSB requires strict linear amplification, flat topping creates severe intermodulation distortion. This results in wide-band spurious emissions known as "splatter," which causes significant interference to adjacent frequencies.