Time domain characterization and modelling of the absorbing clamp. A device for measuring radiated radio frequency power

In the frequency band 30 to 1000 MHz, most of the interference energy from a small appliance is radiated from the cables attached to it. The absorbing clamp, an accepted laboratory method for detecting this interference energy, has been used by the EMC community since 1969. Kwan (1988) has described in conceptual terms the intended mode of operation of the clamp by thinking of it as a discontinuity on the transmission line formed between the attached (mains) cable and the ground plane beneath it. The work presented supports Kwan´s concept and shows how the clamp and the line on which it is placed appears to the equipment under test by using time domain techniques. The test results are examined and compared with those obtained by modelling the clamp and associated cable using transmission line theory. The differences are noted and some explanations are given for these