Which of the following describes a linear amplifier?

A linear amplifier is specifically designed to increase the amplitude of a signal without altering the shape of its waveform. In a perfectly linear amplifier, the output signal is an exact, scaled-up replica of the input signal. This characteristic is crucial for modulation modes that rely on precise amplitude variations, such as Single Sideband (SSB) and Amplitude Modulation (AM). If the amplifier were non-linear, it would distort the peaks and valleys of the waveform, ruining the transmitted voice or data and creating severe splatter on adjacent frequencies. Class C amplifiers and frequency multipliers are intentionally non-linear and would heavily distort these complex waveforms, proving that not all amateur RF amplifiers are linear.