Adjacent Signal Interference

Operational requirements often make it necessary for several transmitters and receivers to operate in close proximity with small frequency separations. The important interference parameters that limit operation under these conditions are transmitter emission spectra, intermodulation, cross-modulation, and desensitization. This paper discusses the EMC problems produced by strong interfering signals in the neighborhood of the receiver tuned frequency. The region of concern, in a typical receiver, may consist of a considerable number of channels on both sides of the receiver-tuned frequency. This paper outlines methods that may be used to calculate the interference resulting from adjacent signals; presents mathematical models that describe the significant effects (such as intermodulation, cross-modulation, and desensitization); and describes methods for utilizing spectrum signature data for evaluating the models for a specific equipment. In addition, for cases where specific receiver measurements are not available, the paper presents general receiver models that have been derived from an analysis of spectrum signature data. The results of the work described in this paper will help to provide an understanding of the basic factors that contribute to the receiver susceptibility to interfering signals in adjacent channels. This information may be used by interference analysts in the calculation of receiver susceptibility and the generation of realistic EMC specifications, and by equipment designers to develop less susceptible equipments.