原创 What is carrier-to-noise ratio?

机顶盒的Tuner性能测试时常用的测试指标.它与硬件和Tuner驱动有关。以下是它的定义。

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.

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 P_c and the noise level, also in microwatts, is P_n, then the carrier-to-noise ratio, C/N, in decibels is given by the formula

C/N = 10 log₁₀(P_c/P_n)

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.