18 Measurement of system parameters
In any communications system the most important parameter is the signal quality or signal to noise ratio (S/N ratio) (see Noise, p. 232). In the general sense, noise is considered to be the summation of all unwanted effects or artifacts superimposed upon the signal due to nonlinearity, in all parts of the link that produce distortion and interference, plus random noise from natural sources. The S/N ratio is thus the power ratio (or in certain cases, the voltage or current ratios) of the wanted signal level to the total noise component. In an analogue system, such effects will distort the signal waveshape and this will be obvious to the ear or eye. Various techniques can be applied that minimise the noise effects ...
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