Some Notes on Noise Figures

The subject matter of this paper first appeared in the form of laboratory reports. Outside interest in these reports prompted the preparation of the material for publication. Despite the attention given to noise and noise figures in the literature, the basic concepts are still little understood by the average engineer. This paper takes up the basic ideas and definitions proposed by H. T. Friis and presents them in a form that is more easily understood. Naturally, complete generality is not achieved, and the conclusions are subject to restrictions. Nevertheless, useful results are obtained. Subjects treated include expositions of the meaning of the "available gain," and the derivation of simple noise-figure formulas for many types of circuits in common use.