If the overall gain of an amateur station is increased by 3 dB the ERP (Effective Radiated Power) will:

The decibel (dB) is a logarithmic unit used to express the ratio of two values of a physical quantity, such as power. A fundamental rule of thumb in radio electronics is that an increase of 3 dB represents a doubling of power. Because Effective Radiated Power (ERP) is directly proportional to the overall system gain, raising the gain by 3 dB will cause the ERP to double. Conversely, decreasing the gain by 3 dB would cut the ERP in half. Answers suggesting the power would remain the same or decrease by a flat wattage ignore the logarithmic nature of decibels, which represent multiplication factors rather than simple addition or subtraction.