A TEM cell is a stripline device for radiated emissions and immunity testing of electronic devices. It is not a substitute, but because of its size and cost its a convenient alternative to measurements in an anechoic chamber. A TEM cell is made up of a septum, the conductive strip in the centre section and walls which are connected to ground. The geometry is configured to present a 50Ω stripline. The device under test (DUT) is positioned between the bottom wall and the septum. The TBTC1 is a so called “open TEM cell”, which has no side walls for convenient placement of the DUT. It may pick up RF background noise, which can be taken into account by doing a measurement of the cell output signal prior to powering on the DUT.
A DC LISN (Line Impedance Stabilisation Network) is used for the measurement of conducted emissions, from DC powered devices. The LISN is positioned within the supply line of the DUT (Device Under Test). Conducted noise which is present at the supply terminals of the DUT can be measured at the BNC connector using a spectrum analyser or a measurement receiver. The source (supply) terminal and the DUT terminal are decoupled by a 5µH inductor.
Near-field probes act like wideband antennas, picking up radiated emissions from components, PCB tracks, housing openings or gaps and from any other parts that could be emitting RF energy. Scanning a probe over the surface of a PCB assembly or housing quickly identifies locations which emit electromagnetic radiation. By changing to a probe with a smaller size, the source of the emissions can be narrowed down further. The probes can also be used for for RF immunity tests, by feeding a RF signal into the probe and radiating it into potentially vulnerable areas of the circuit. The probes can also be used for repair or debugging, to track down faults in RF circuits by non-contact measurement of RF signal levels.
A Spectrum analyser presents a power by frequency display that amongst other things, can be used to display the results of measurements taken out by any of the above tools.
By using a spectrum analyser you can easily see in what frequency band your tested devices are emmitting and at what power, this makes the spectrum analyser a must have when working with EMC pre-compliance testing.