Shielding techniques for communication cable - An update

Techniques of shielding against electronic interference (EI) in the frequency range 1-100 MHz are reviewed. The various sources of EI are discussed, including electrostatic induction; electromagnetic induction; magnetic induction; and electromagnetic pulse (EMP). The effectiveness of different shielding constructions is examined with respect to new FCC regulations for electromagnetic compatibility. Among the shielding constructions examined are: braids; tape shield; and foil designs. The relative transfer impedance of the shielded cable was measured following exposure to EI from the different sources, and the results were compared. The ideal shield for use at frequencies of 1 MHz was a solid copper tube. For frequencies greater than 10 MHz, however, a composite foil/braid was found the most effective shield construction.