What can be done to prevent unwanted oscillations in an RF power amplifier?

Unwanted oscillations, often called parasitic oscillations, occur when unintended feedback within an amplifier causes it to act like an oscillator. These oscillations usually happen at VHF or UHF frequencies rather than the desired operating frequency, potentially damaging the amplifier and causing severe out-of-band interference. To prevent this, parasitic suppressors (typically a small resistor wrapped with a few turns of wire) are placed in the plate, grid, or collector leads to choke off VHF/UHF feedback. Additionally, 'neutralizing' the stage by feeding a small amount of out-of-phase energy back to the input cancels out internal feedback capacitance. Tuning the amplifier for maximum power or minimum loading does not address the internal stray capacitance that causes these self-sustaining oscillations.