What does an SWR reading of 4:1 indicate?

SWR, or Standing Wave Ratio, is a measure of how well the impedance of the transmitter, feed line, and antenna match each other. A perfect match is 1:1, meaning all available power is transferred to the antenna and successfully radiated. An SWR reading of 4:1 is quite high and indicates a significant impedance mismatch, meaning a large portion of the transmitter's power is being reflected back down the feed line toward the radio. The distractors involving dB loss or gain are incorrect because SWR is a ratio of voltages, not a direct measurement of decibel gain or loss.