In electronic Telecommunication and , the factor of noise is the relationship between the signal reports/ratios on Bruit (expressed in power) at exit and entry of a stage. It thus characterizes the degradation brought by this stage.

In particular, in the case of a Radioelectric receiver presumedly linear, one compares the power of noise with the exit with that which one would have if there were in this receiver no source of noise other than those which exist in the impedance external connected to the entry, supposed with a specified temperature, usually 290°  K. It is thus about a measurement of performance of the receiver.

The factor of noise is given by:

$F\; =\; \backslash \; frac$ where S/N is the Rapport signal on noise ( Signal to Noise ratio ).

One frequently expresses the factor of noise and the signal report/ratio on noise in units logarithmic curves, the decibels. The reports/ratios then take the form of differences between values in dB.

When several electronic elements are put in series, the total noise is found by the formula of Friis :

$F\; =\; F\_1\; +\; \backslash \; frac\; \{F\_2\; -\; 1\}\; \{G\_1\}\; +\; \backslash \; frac\; \{F\_3\; -\; 1\}\; \{G\_1\; G\_2\}\; +\; \backslash \; frac\; \{F\_4\; -\; 1\}\; \{G\_1\; G\_2\; G\_3\}\; +\; \backslash \; cdots\; +\; \backslash \; frac\; \{F\_n\; -\; 1\}\; \{G\_1\; G\_2\; G\_3\; \backslash \; cdots\; G\_\; \{n-1\}\},$

where F_n is the factor of noise F for the N ^ème element and G_n is the profit (numerical and not in dB) of the N ^ème element.

The electronic elements without profit (e.g. Attenuator) have a factor of noise equal to their attenuation in dB.

In the systems heterodyne receiver S, the power of exit associated with the noise includes the random contributions of the Fréquence S-images coming from the transformation. However, the fraction ascribable to the thermal noise at the entry includes only the part appearing in the exit via the principal transformation and not that which appears in the transformation of the frequency image.

See too

Related articles

• Noise
• signal Report/ratio on thermal noise
• Noise

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