Metallic communications (i.e. wires and cables) all suffer from being ‘unintentional antennas’, which means that some of their internal signals leak into the environment as RF emissions. A physical structure that can leak signals into the environment can also pick up electromagnetic noise from the environment and inject it into the signal. Cables are of course passive, that is, they are not of themselves affected by, and do not generate, interference. But their configuration is directly responsible for how they couple interference to and from the victim or source circuits.

We use cable shielding and filtering to mitigate these problems – techniques which can be surprisingly costly, especially if not designed-in from the start of a project. Understanding cable coupling is critical to minimising the installed cost of a complete system.

Unshielded cables

Cable configurations can affect coupling with the environment even if they don't carry a shield

Cable routing and segregation

Cable routing techniques are used to reduce the ‘unintentional antenna’ efficiency of cables, and also to prevent low-frequency crosstalk and RF coupling between cables in a system or installation

Cable shielding

Cable shielding (or screening) is used to reduce the unwanted emissions (‘leakage’) from the signals carried by a cable, and also to improve the immunity of the signals in the cables to ambient electromagnetic noise

Cable connectors

To be able to use shielded cables effectively, connectors and glands used with them must carry and/or bond to the cables’ circumferential shields without compromising the effectiveness of the overall shield

Cable ferrites

As a simple retrofit, a ferrite sleeve placed over a cable can attenuate the common mode currents on the cable without affecting the wanted internal signal, and thereby reduce emissions and susceptibility via the cable