1961 (ed. 3) xiii. 358 The ratio of maximum to minimum voltage at the crest and trough of the standing wave, is called the voltage standing wave ratio (v.s.w.r., often abbreviated to s.w.r.).
1976 Feb. 62/2 The column will also contain useful information about adjusting antennas, dope about SWR (standing-wave-ratio) measurements, and all that good stuff.