Screening of cables and connectors

Cable and connector screening is given as transfer impedance, which relates a voltage seen inside the component to the current on its outside. One transient disturbance comes from switching on the local mains network, which results in large RF currents flowing in an instrument cable nowhere near the original source. The effect of this current on cables and connectors is assessed using their transfer impedance and it is explained why application of this test in real life depends critically on the electrical length of the cable. The screening performance of different components is compared and an attempt made to explain why some are much better than others. This is extended to outlining the effect of cable construction and detailing the importance of connector design. In conclusion an outline is given of the problems which are found in braid optimisation and how the measurement of cable and connector screening can be used in system design-not just to show one to be better or worse than another