The noise figure is thus the ratio of actual output noise to that which would remain if the device itself did not introduce noise. In heterodyne systems, output noise power includes spurious contributions from image-frequency transformation, but the portion attributable to thermal noise in the input termination at standard noise temperature includes only that which appears in the output via the principal frequency transformation of the system, and excludes that which appears via the image frequency transformation.
In telecommunication, noisefigure (NF) is the ratio of the outputnoise power of a device to the portion thereof attributable to thermal noise in the input termination at standardnoise temperature (usually 290 K).
The noisefigure is thus the ratio of actual outputnoise to that which would remain if the device itself did not introduce noise.
In heterodynesystems, outputnoise power includes spurious contributions from image-frequency transformation, but the portion attributable to thermal noise in the input termination at standardnoise temperature includes only that which appears in the output via the principal frequency transformation of the system, and excludes that which appears via the image frequency transformation.
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