Screening effectiveness measurement of a coaxial cable isolator

Coaxial cable isolators are designed to limit the amount of current flowing on the screen of a coaxial cable as a result of earth loops, an AC mains power contact, or mains isolation fault. Invariably, isolators involve the "breaking" of the screen, creating the potential for signal leakage into and out of the cable system through the isolator. Techniques for the measurement of the screening effectiveness of isolators have utilized various approaches including the International Electrotechnical Commission's (IEC's) absorbing clamp method. This paper demonstrates that results obtained using the absorbing clamp method can be influenced by the interaction between the isolator and the attached cable, which makes reliable and repeatable measurements difficult. It is shown that the IEC's line-injection method provides a simpler, more reliable means of assessing the screening effectiveness of a coaxial isolator.