Practical approach to IEC 61000-4-6 testing

The injection method defined in the standard IEC/EN 61000-4-6 consists in substitution i.e. the stress level to be injected during the test at the RF-Port is set prior to the test with defined load impedances at the EUT-Port and AE-Port of the coupling decoupling appliance. Impedance of the test generator connected to the RF-Port (50 Ω) along with possibly decoupling impedance and load impedance at the AE-Port build impedance of the disturbance source. The test is performed properly if the impedance of the disturbance source during setting the level and during the test is the same. Therefore it is very important to keep the load impedance at the AE-Port during setting the level and during the test unchanged The standard defines different appliances for injection of RF disturbances. Coupling decoupling networks (CDNs) are preferred injection clamps such as electromagnetic (EM) clamp or current injection (CI) clamp are also accepted but only if application of CDNs is not possible. CDNs, unlike injection clamps, are insensible to impedance variations at the AE-Port. The big advantage of injection clamps contrary to CDNs is noninvading character of coupling. It should be not underestimated by in situ measurements of large systems or installations by interfering the supply lines. The author proposes the method of stabilising the impedance of the disturbance source by coupling the stress to the AC supply line with the EM clamp. The method is based on slide modification of the artificial mains network (AMN). AMN is indispensable for conducted emission tests. The method can be directly applied for CI clamp.