An impedance mismatch can be also quantified with the standing wave ratio ( SWR or VSWR for voltage ), which is connected to the impedance ratio and reflection coefficient by : VSWR = \ frac { | V | _ { max } } { | V | _ { min } } = \ frac { 1 + | \ Gamma | } { 1-| \ Gamma | }, where \ left | V \ right | _ { min, max } are the minimum and maximum values of the voltage absolute value, and the VSWR is the voltage standing wave ratio, which value of 1 denotes full transmission, without reflection and thus no standing wave, while very large values mean high reflection and standing wave pattern.
42.
In electrical systems involving transmission lines ( such as radio and fiber optics ) where the length of the line is long compared to the wavelength of the signal ( the signal changes rapidly compared to the time it takes to travel from source to load ) the impedances at each end of the line must be matched to the transmission line's characteristic impedance ( Z _ c ) to prevent reflections of the signal at the ends of the line . ( When the length of the line is short compared to the wavelength, impedance mismatch is the basis of transmission-line impedance transformers; see previous section . ) In radio-frequency ( RF ) systems, a common value for source and load impedances is 50 antenna ( 37 ohms with an ideal ground plane; it can be matched to 50 ohms by using a modified ground plane or a coaxial matching section, i . e ., part or all the feeder of higher impedance ).
