Use of Frequency-Conversion Diagrams

The mathematical difficulties involved in analytical treatment of single-mesh mixer circuits with diodes and crystals lead us to consider other methods for the determination of important mixer characteristics. This paper briefly reviews the rectification-diagram method as applied to large-signal detectors, and presents for consideration the Chaffee conversion-diagram method, which treats mixer circuits in the same way as large-signal detector circuits. To demonstrate this method, the rectification diagram for a large-signal detector is used to illustrate conditions when two voltages of different frequencies are applied to the nonlinear element; and it is shown how this rectification diagram may be given a more suitable form, describing the frequency-conversion properties of the nonlinear element. The path of operation in this new so-called frequency-conversion diagram yields numerical values for the output (intermediate-frequency) voltage and current. The equations for the diagram are given as well, and may be used for calculations pertaining to the modulation envelope of the produced intermediate-frequency wave. The measurement setup used to investigate the possibilities of the conversion-diagram method is briefly described, and the frequency-conversion diagrams obtained for ultra-high-frequency diodes and crystals are reproduced in the text. Some of the quantities that can be read off from frequency-conversion diagrams are illustrated by graphs and are discussed further in the paper.