ABSTRACT
One of the major reasons equipment fails radiated emission requirements is radiation from digital signals, either directly from the printed circuit board (PCB) or from PCB-sourced common-mode (C/M) noise voltage driving attached cables. Even when equipment is contained in a totally shielded enclosure, noise voltage generated across a PCB to which unshielded and unltered interface cables are connected can result in a sufciently high noise current to fail radiated emission requirements. In extreme cases, PCB-generated noise has resulted in equipment failure of commercial radiated emission requirements with shielded cables connected to a PCB metal faceplate, which in turn was connected to a shielded enclosure. If the radiated emission requirements are of the stringent MIL-STD-461 or DO-160, the use of a shielded enclosure is almost mandatory.
