A Line Impedance Stabilization Network (LISN) can provide a relatively simple and affordable way to perform conducted emission tests on power lines of devices that have to be tested for EMC/EMI pre-compliance. A LISN is used for basic pre-compliance testing in an ordinary lab and will most likely make testing in a full-compliance test laboratory for certification at a later stage less costly, because less or no changes have to be made to a design to make it EMC/EMI compliant. A full compliance test in a certified lab is expensive, so every issue you can tackle in your own lab can save a lot of time, money, and frustration for that matter. The LISN [1] is connected between the power source and the Equipment Under Test (EUT) (see Figure 1), and provides a normalized 50 Ω power line impedance, making the tests independent from the physical power source impedance. In addition to that, its low-pass input filter blocks injection of RF interference from the power source and/or noise on the power cables into the EUT. A third function of a LISN is that it offers one (or more) 50 Ω output(s) that can be connected to a spectrum analyzer or other measurement equipment to evaluate the conducted emission on the power lines. In most cases, these measurement outputs protect the spectrum analyzer inputs against transients and overvoltage. Any RF noise generated by the EUT is separated by the LISN and fed to the spectrum analyzer for measurement or recording.
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