What measurement can be made of a single-sideband phone transmitter's amplifier by performing a two-tone test using an oscilloscope?

A two-tone test observed on an oscilloscope is the standard method for measuring the amplitude linearity of a single-sideband (SSB) transmitter's amplifier. Linearity dictates how faithfully the amplifier reproduces the input signal at a higher power level without distorting its shape. Because SSB is a form of amplitude modulation, the RF envelope constantly changes in amplitude to represent the audio signal. If the amplifier is non-linear—perhaps due to being driven too hard—the peaks of the waveform will be clipped or "flat-topped." This non-linearity generates unwanted distortion and splatter on adjacent frequencies. The two-tone test is exclusively used for evaluating this amplitude linearity. It has nothing to do with measuring frequency modulation (FM) parameters, such as frequency deviation or percent of frequency modulation, nor does it measure carrier phase shift.