Definition
A measure of how efficiently radio-frequency power is transferred from a transmitter through a transmission line to an antenna. It is the ratio of the maximum voltage to the minimum voltage of the standing wave that forms on the line when the antenna and the line are not perfectly matched. A VSWR of 1:1 means a perfect match and full power transfer; higher ratios mean more power is being reflected back toward the transmitter instead of being radiated.
Plain English
A number that tells you how well a radio's antenna and cable are matched. The closer the number is to 1, the better the radio is sending its signal out. A higher number means some of the signal is bouncing back instead of going out as a transmission.
Context Anchor
Seen in aircraft radio, antenna, communication, navigation, and avionics maintenance discussions.
Derivation
The name describes what is being measured: the ratio of the highest to lowest voltage points along the line when forward and reflected radio waves combine to form a stationary -- or standing -- pattern. The wave appears to stand still rather than travel, because the peaks and troughs stay at fixed points on the line.
Why Pilots Care
High values reduce radio range and risk damaging the transmitter through reflected power.
Analogy
Think of water flowing through a hose into a sprinkler. If the sprinkler matches the hose, all the water sprays out. If it doesn't, some water pushes back up the hose. VSWR measures how much is pushing back.
Grounding Statement
A good antenna system sends most of the radio signal outward; a poor match sends more of it back toward the radio.
Intuition Check
Do not read “standing” as meaning the aircraft or antenna is stationary. Here, “standing wave” means a radio-wave pattern that stays in place along the cable because outgoing and reflected energy overlap.
Example Sentence 1
The avionics technician measured a VSWR of 1.2:1 on the comm antenna, confirming the installation was within tolerance.
Example Sentence 2
A voltage standing-wave ratio above 2.5 caused weak transmissions until the corroded connector was replaced.