Conducted Emission

When testing the conducted emission, the currents and voltages of outgoing cables are measured in a particular (low) frequency range. Outgoing cables are most of the time too short to act as good antenna’s or they are too large to fit in an anechoic chamber. Even at an open area test site (OATS) there are some problems with reproducibility because of the cable positioning possibilities at low frequencies.

The common mode (CM) current in a cable is responsible for the radiation coming from that cable. With a coupling / decoupling network (CDN) (see photo conducted immunity) this current is measured as a voltage over an impedance of 150 ohm, the average common-mode impedance of a typical cable.

When using a current clamp the current is measured directly without a decoupling unit with 150 ohms. The Absorbing Clamp is a combination of a current clamp with a decoupling unit. This combination is very helpful when measuring the CM-current in a cable that can not be cut in half (real time measurement or there is no CDN available for the particular cable). When measuring with an absorbing clamp the disturbance is measured in dBpW and not in amps or volts. The frequency range that is covered with these methods is from about 150 kHz up to 230 MHz. Some emission measurements are done up to 1 GHz using an absorbing clamp.

The most famous conducted emission measurement of all is the line disturbance test. In this case the line impedance is stabilized to a known impedance. This is done because of the big differences in line impedance's over the whole continent. So for this frequency range (9 kHz - 30 MHz) the line is filtered and has a stable impedance (50 Ohm // 50 microHenry). The disturbance voltages over this ‘new’ impedance are measured. The line impedance stabilization network (LISN) is also called an Artificial Mains Network (AMN). An example of a conducted emission plot can be seen at the bottom of this page.