How is the efficiency of an RF power amplifier determined?

Efficiency is a fundamental measure of how well a device converts its primary power source into useful output. For an RF power amplifier, the primary job is to take electrical power from a power supply (DC input) and convert it into a transmitted radio frequency signal (RF output). To calculate this electrical efficiency, you divide the useful work done (the RF output power) by the total power consumed to do that work (the DC input power). The result is usually multiplied by 100 to yield a percentage. Other formulas, such as dividing RF output by RF input, actually calculate the amplifier's power gain rather than its efficiency. You must compare the RF out to the DC in to see how much supply power was successfully converted versus lost as heat.