Present emission standards are developed with respect to analog communication services. Therefore, knowledge of how relating present standards to the impact on digital radio receivers must be available for sg stem design purposes, For a digital radio receiver, the bit error probability (BEP) is often used to show the impact of the receiver performance from a disturbing signal. A simple, previously proposed method relates present emission standards to the BEP for broad-band (BB) disturbance, This method has to be modified for use on narrow-band (NB) disturbance such as the NE spectral components from periodic signals. In this short paper, a method based on a modification of the earlier method is presented for this NE disturbance. This represents typical disturbance from information technology equipment working with periodic signals, The conclusion is that the method presented delivers a useful value of the BEP, which can be used when radiated emission requirements are to be chosen on electronic equipment co located to digital radio systems.