Apparatus and methods for testing immunity to and emission of electromagnetic fields

An electromagnetic compatibility test apparatus comprises a conductive boundary 2 arranged to enclose the equipment under test (EUT) 1. A cable 3 linked to the EUT 1 passes through a filter arrangement 4 before passing through the said boundary 3 as it approaches the EUT 1. Switch means 6 is arranged which can be activated to couple an element of the cable 3 to the said conductive boundary 2. The switching means 6 may then be controlled in such a manner as to quickly identify a cable connection condition which is near to that which provides the worst-case of electromagnetic coupling. The switching means 6 may be a fast acting PIN diode switch, an electromechanical relay or an electrically or optically activated transistor. The filter arrangements may involve ferrite sleeves, common mode choke arrangements, decoupling capacitor arrangements and/or one or more absorbing clamps.