The input and output power characteristics of the RF amplifier are the main characteristics, because increasing the signal strength is the main purpose of the amplifier. The maximum and nominal range of input and output power will be specified for the RF power amplifier based on specific conditions.

These specifications will be further extended to the maximum and nominal ranges of input and output voltages and currents. If the power, current or voltage appearing at the input or output exceeds the specifications, it may cause undesirable operation or even damage the device.

An important note about amplifiers used in pulse or signal modulation in other applications is that certain types of modulation may change the power, voltage, or current of a basic continuous wave signal, which may cause certain recommended limits to be exceeded. Therefore, it is necessary to understand the input and output power characteristics over the entire frequency to ensure an acceptable operating range at each frequency.

The general parameter used to represent the input and output power characteristics of any amplifier is the gain, or the comparison of the output signal power and the input signal power. For RF amplifiers, this parameter is given over the entire frequency range. Since the gain of the RF amplifier will not be completely consistent over the entire frequency, the gain flatness of the frequency response can be obtained by measuring the peak-to-peak gain behavior.

In some cases, the signal may appear at the output port of the RF power amplifier through reflection or other system dynamics. The output-to-input gain or reverse gain is used to evaluate the effects of the signals present on the amplifier output, the amplifier input, and the upstream signal chain.

No physical device will output all input power and input signal power. There are RF conversion losses, internal resistance losses, impedance mismatches, and coupling effects. These powers will pull power out of the amplifier's output.

Compared with the realized output power, the measure of the power input to the amplifier is called efficiency. Since this is the main consideration in many RF power amplifier applications, the power added efficiency includes the RF input power in the calculation.