5.7 Noise Measurement

For many applicationsMeasurement knowing the noise properties of a produced device or system are essential. One usually has to know what is the contribution of the circuit to the overall noise at the output, especially when fable signals are processed as is the case in long distance communications and sensory systems and networks. The aim of the discussion in this short chapter is to give the fundamentals of the noise measurement methods which in generally comes to the measurement of the noise figure of the tested system. Several methods are discussed the main novelty being the introduction of the so called effective noise temperatureEffective noise temperature of the tested system. Setting that value in relation to the excitation source resistance makes it possible to recognize the noise properties of the system under test at first glance. Sophisticated equipment is needed for implementation of any noise measurement method. First, one needs to precisely control the temperature of the noise source used as a reference, meaning a temperature-controlled chamber is needed. Second, since the noise spectrum is measured, selective equipment (1 Hz bandwidth) must be applied such as network analyzerNetwork analyzer or vector analyzerVector analyzer. In some cases a low-noise signal generatorSignal generator is needed with well-defined passband width and location. Al together, noise measurement, especially at very high frequency is a sophisticated and very expensive activity. Add to that the need for highly skilled engineering staff.