24 Principles of Synchronous Digital Hierarchy
discharges and thunderstorms. Solar and cosmic radiation also create noise.
However, the second biggest source of noise is industrial activity, which
may include the ignition of automobile engines, aircraft, switching surges of
motors and power transmission grids, and leakages from high voltage lines.
2.2.2.2 Relevance of Type of Noise
As mentioned above, white noise and industrial noise are the major contrib-
utors to the noise activities as far as communication systems are concerned.
While the noise generated by electronic devices is generally a white noise
which is of low power but high band width, and is always present, the indus-
trial noise is generally of impulse type, inducing imp ...