Some Considerations Governing Noise Measurements on Crystal Mixers

The general principles of analysis and measurement of noise in radio receivers are discussed starting with basic definitions and following with a derivation of the fundamental equations for noise and noise figures of single and cascaded networks. A treatment of the noise generated in a crystal rectifier, when used as the first detector in a superheterodyne receiver, is given in which the "noise temperature" of the crystal is defined and the contribution by virtue of this noise temperature to the over-all noise figure of the receiver is indicated. The problem of designing a noise-measuring set is treated in sufficient detail to show how the noise temperature of a crystal rectifier can be measured independently of its other properties.