|Definition:|| the ratio, generally expressed in decibels, of the power of the wanted signal to that of the coexistent noise at a specified point in a transmission channel, usually at the receiver output, under specified conditions
NOTE 1 – The signal cannot generally be separated from noise, and in practice the ratio (signal+noise) to noise is measured.
NOTE 2 – The specified conditions comprise among others:
– the nature and characteristics of the wanted signal,
– the nature and characteristics of the noise,
– the receiver and antenna characteristics such as the bandwidth.