EMC Figure of Merit for Receivers

In order to evaluate receiver susceptibility to interference, it is necessary to have some means of measuring and specifying receiver characteristics. One major source of receiver susceptibility information is the spectrum signature measurement program performed under MIL-STD-449C. Although many of the important receiver interference effects result from the same basic cause (i.e., undesired nonlinearities) and are influenced by the same basic factors such as selectivity and gain, under the current spectrum signature measurement program, each type of interference is measured separately as if they were completely unrelated. As a result, it is expensive and time consuming to obtain a complete "spectrum signature" for a receiver. Furthermore, receiver interference specifications have adopted the same general philosophy of treating each of the interference effects separately, and consequently, it is prohibitively expensive and difficult to establish any form of production line EMC quality control. What is desired is a receiver "figure of merit" that is simple to measure and describes the overall susceptibility of a receiver to interference. If this elusive but needed receiver "figure of merit" can be defined, it would provide a basis for receiver EMC specification, measurement, comparison, and quality control. This paper discusses a single receiver parameter that is easily measured, and may be used directly to evaluate receiver susceptibility to desensitization, cross modulation, and intermodulation. Furthermore, because this parameter provides an overall measure of the combined effects of RF selectivity, gain, and nonlinearity, it provides some information on receiver spurious response characteristics.