What is carrier-to-noise ratio (C/N) and how is it measured?
Carrier to noise ratio is the ratio of the carrier signal power to the noise power in some specified channel, usually expressed in decibels (dB). For the analog channels the noise is assumed flat and the result of thermal and amplifier noises. Measurements are made with a spectrum analyzer. The carrier is used as a reference and the noise is usually measured using the “noise marker” of the spectrum analyzer set to a quiet spot in the band. The noise marker reading is now normalized to 4 MHz and the measured C/N is the ratio of the carrier to the normalized noise level, measured in dB. The 4 MHz normalization frequency is for the American standard, other standards may require a different bandwidth.
