Interference is the sum of all electromagnetic signals, both wanted and unwanted, that are present in a cable. This can include signals that are generated externally such as radio waves, or signals that are generated within the cable itself such as impulses from electrical equipment. Interference can be caused by a variety of sources, including crosstalk between adjacent cables, electromagnetic radiation from nearby power lines, and signals from other electronic devices.

Interference can cause a variety of problems for cables, including signal degradation, distortion, and loss of signal. In order to minimize the impact of interference, cables need to be designed and installed in such a way that reduces the amount of interference they experience. This can include shielding the cables, using special cables designed to reduce interference, and avoiding placing cables in areas with high levels of electromagnetic radiation.

Interference can also be used to improve the performance of cables. By using constructive interference, signals can be amplified and distorted signals can be reduced. This can be done by connecting cables of different lengths together in series, so that the waves produced by the cables are in phase with each other and their amplitudes add. Similarly, destructive interference can be used to reduce the intensity of a signal, by connecting cables of the same length in parallel so that their waves are 180 degrees out of phase and their amplitudes cancel.