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The expressions for available power gain and noise measure of linear two-ports are introduced in terms of the two-port parameters and the gain and the noise parameters, respectively. Their graphical representations on the source admittance plane with rectangular coordinates are also shown. Furthermore, it is shown that the behavior of available power gain, noise figure, and noise measure can be represented on the Smith-chart or the complex reflection coefficient plane of the source admittance. It is more convenient to investigate the gain and noise performance of amplifiers over a wide range of source admittance in this representation than with rectangular coordinates. As an example of the graphical representation the gain and noise performance of a microwave transistor is illustrated on the Smith-chart.