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The Probability Scoring Model used for electromagnetic compatibility analysis considers the probability of correct information transfer, written as P(R+), to determine link quality. Experience has shown that the smallest value of articulation index (AI) which consistently provides correct information transfer in the presence of normal language configuration is 0.7 in a scale ranging from 0 to 1, and that the largest value of AI for a nonuseful link is 0.3. AI has been shown to be a function of the link description (receiver/transmitter type and frequency), the interferer description (type and frequency), and the strength of the desired and interfering signal, SRF and I, respectively; hence, for any given communications system of such configuration that the link and interferer descriptions and frequencies are known, AI can be established as a function of SRF and I. Determination of AI requires the use of the Voice Interference Analysis System (VIAS), test equipment which is costly and not readily available to all potential users of the Electromagnetic Environmental Test Facility (EMETF) Probability Scoring Model. However, receiver audio signal-to-noise ratio (S/N) can be shown to be a function of the same variables. A nonlinear regression analysis line has been established by relating empirical audio S/N values to AI for AM, FM, and SSB link and interferer modulation combinations. Typical military communications sets were used. As a result of this analysis, the criterion values of 0.3 and 0.
Sorkin et al. (Mon,) studied this question.