Carrier to Noise Ratio

In communications, the carrier-to-noise ratio, often written CNR or C/N, is the signal-to-noise ratio (SNR) of a modulated signal. The CNR is the quotient between the average received modulated carrier power C and the average received noise power P after the receiver filters. The aim of the term is to distinguish the CNR of the radio frequency passband signal from the SNR of an analogue base band message signal after demodulation, for example an audio frequency analogue signal. If this distinction is not necessary, the term SNR is often used instead of CNR, with the same definition.
See more at Wikipedia.org...

In radio receivers, the ratio of the level of the carrier to that of the noise in the intermediate frequency (IF) band before any nonlinear process, such as amplitude limitation and detection, takes place. (188 ) Note: The CNR is usually expressed in dB.