A power management system is provided for a software-defined radio. The power management system includes: an antenna; a regulated power supply; a power amplifier; and a digital signal processor. A software-implemented power supply calculator and power supply adjustor are operable within the digital signal processor. The power supply calculator receives an indicator of a type of waveform to be transmitted by the radio and determines the drain voltage for the power amplifier based on the waveform indicator. The power supply adjustor receives forward power and reflected power values from the antenna and computes a voltage standing wave ratio (VSWR). The power supply adjustor further computes an adjustment for the drain voltage based on the VSWR.