Editing Input impedance (section)

===Radio frequency power systems===

Signal reflections caused by an impedance mismatch at the end of a transmission line can result in distortion and potential damage to the driving circuitry.

In analog video circuits, impedance mismatch can cause "ghosting", where the time-delayed echo of the principal image appears as a weak and displaced image (typically to the right of the principal image). In high-speed digital systems, such as HD video, reflections result in interference and potentially corrupt signal. 

The standing waves created by the mismatch are periodic regions of higher than normal voltage. If this voltage exceeds the [[dielectric breakdown]] strength of the insulating material of the line then an [[Electric arc|arc]] will occur. This in turn can cause a reactive pulse of high voltage that can destroy the transmitter's final output stage.

In RF systems, typical values for line and termination impedance are [[50 Ω]] and [[75 Ω]].

To maximise power transmission{{what|reason=What is the relation between (non-conjugate) impedance matching at termination of a line, and conjugate-matching of source and load impedance (output and input) across a port? These appear to have two different effects, yet they are intermixed without any transition.|date=January 2017}} for radio frequency power systems the circuits should be ''[[complex conjugate]] matched'' throughout the [[power chain]], from the [[transmitter]] output, through the [[transmission line]] (a balanced pair, a coaxial cable, or a waveguide), to the [[antenna (radio)|antenna]] ''system'', which consists of an impedance matching device and the radiating element(s).