Electrical characteristics of balanced cables: NEXT and FEXT parameters
The main influences in symmetrical cables are transient influences at the near and far ends. The influences are caused by parasitic electromagnetic and capacitive coupling between pairs of the same cable or several closely spaced cables. Devices for diagnostics and localizing faults in metallic cables are used to assess such transient influences. The primary method of reducing such influences is to twist the copper pair strands. The most stringent requirements are structured cabling with a wide range of operating frequencies. For example, no twisting is allowed at a distance of no more than 1/2 inch from the two cable segments' connection point. A transient influence measure is: - Near End Transient Attenuation (Near End Crosstalk, NEXT) - Far End Transient Attenuation (Far End Crosstalk, FEXT). These parameters allow you to assess the suitability of symmetric cable pairs for high-speed data transfer. The transient attenuation NEXT and FEXT can be expressed as the logarithm of the