What is standing wave ratio (SWR)?

Standing Wave Ratio (SWR) is a fundamental concept in radio that describes how efficiently radio frequency (RF) power is transferred from a source, through a transmission line, and into a load (such as an antenna). When the impedance of the antenna perfectly matches the impedance of the feed line, all the forward power is radiated into space. However, if there is an impedance mismatch, some of that power reflects back down the line toward the transmitter, creating "standing waves" of voltage and current along the cable. Therefore, SWR is a direct measure of this impedance match. A perfect match yields an SWR of 1:1, whereas higher numbers indicate poorer matching and more reflected power. It has nothing to do with amplifier efficiency or the quality of your station's safety ground.