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What is VSWR - Voltage Standing Wave Ratio

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    What is VSWR - Voltage Standing Wave Ratio

    VSWR or voltage standing wave ratio is a phenomenon that occurs on radio frequency feeders. VSWR, voltage standing wave ratio is an important parameter in many areas, and especially where transmitters are used.
    When looking at VSWR it is necessary to look at feeder and load impedances. It is found that to transfer the maximum amount of power from a feeder to a load, the two must have the same impedance. Coaxial feeder, twin-line feeder, waveguide and strip-line feeder all have a characteristic impedance. If the load has a different impedance then not all the power can be transferred and the remaining power is reflected back along the feeder.
    The voltages and currents from the forward and reverse power combine together and set up standing waves along the feeder. It is found that peaks and troughs occur as a result of the standing waves. These peaks and troughs can rise to twice the voltage of current for a complete mismatch, i.e. infinity to 1 VSWR.
    For lesser values of VSWR, the plot of voltage against current along the feeder is less marked.
    Accordingly it is possible to defined the voltage standing wave ratio, VSWR as the maximum voltage divided by the minimum voltage.
    The reflection coefficient is also a very useful quantity when looking at VSWR. This is the voltage of the forward waveform divided by the voltage of the reflected waveform. It is also possible to obtain the VSWR from a knowledge of the forward and reflected powers. These are all described in the video.

    More information about Voltage Standing Wave Ratio, VSWR can be found at:

    73 Al 4L5A