Electromagnetic interference and countermeasures on metallic lines for ISDN

Electromagnetic interference on a bus wiring configuration of the ISDN (integrated services digital network) basic interface using metallic telecommunication lines is studied. A simple circuit to simulate terminal equipment unbalance with respect to the ground is developed for measurement purposes, on the basis of the fact that the unbalance weakens the ability to withstand interference. The electromagnetic interference from low-voltage supply lines, analog telephone lines, and broadcasting waves is evaluated by experiments using the circuit, showing that the basic interface is disturbed by the induced voltage because the terminal equipment in the CCITT Recommendation I.430 has too large an unbalance with respect to the ground to maintain transmission quality. Countermeasures to reduce interference are proposed