Effects of Configuration Parameters on the Radiation of the ISDN S-BUS

On the ISDN S-bus, fast digital signals are transmitted over voice graded telephone cables. Radiation of these signals may cause interference to other equipment. In addition, the signals may be intercepted and the original information may be recovered. In this paper, the influence of configuration parameters on the radiation is investigated. For this, the S-bus is simplified into a two-conductor model. Using Transmission Line Modelling, the radiation of this model is computed. The most important cause of radiation is the output unbalance of the transmitter. Cable and termination unbalance are much less important causes. An important parameter that only influences the radiation is the common-mode impedance.