In communications, the carrier-to-noise ratio, often written CNR or C/N, is a measure of the received carrier strength relative to the strength of the received noise. High C/N ratios provide better quality of reception, and generally higher communications accuracy and reliability, than low C/N ratios.
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Engineers specify the C/N ratio in decibels (dB) between the power in the carrier of the desired signal and the total received noise power. If the incoming carrier strength in microwatts is Pc and the noise level, also in microwatts, is Pn, then the carrier-to-noise ratio, C/N, in decibels is given by the formula
C/N = 10 log10(Pc/Pn)
The C/N ratio is measured in a manner similar to the way the signal-to-noise ratio (S/N) is measured, and both specifications give an indication of the quality of a communications channel. However, the S/N ratio specification is more meaningful in practical situations. The C/N ratio is commonly used in satellite communications systems to point or align the receiving dish; the best dish alignment is indicated by the maximum C/N ratio.