Explanation of External Noise:-
Atmospheric noise or static is caused by lighting discharges in thunderstorms and other natural electrical disturbances occurring in the atmosphere. These electrical impulses are random in nature. Hence the energy is spread over the complete frequency spectrum used for radio communication.
Extraterrestrial Noise:- There are numerous types of extraterrestrial noise or space noises depending on their sources. However, these may be put into following two subgroups.
1. Solar noise
2. Cosmic noise
This is the electrical noise emanating from the sun. Under quite conditions, there is a steady radiation of noise from the sun. This results because sun is a large body at a very high temperature and radiates electrical energy in the form of noise over a very wide frequency spectrum including the spectrum used for radio communication.
Cosmic noise:- Distant stars are also suns and have high temperatures. These stars, therefore, radiate noise in the same way as sun. The noise received from these distant stars is thermal noise (or black body noise) and is distributing almost uniformly over the entire sky. We also receive noise from the center of our own galaxy from other distant galaxies.
Man-Made Noise (Industrial Noise):- Man-made noise or industrial- noise is meant the electrical noise produced by such sources as automobiles and aircraft ignition, electrical motors and switch gears, leakage from high voltage lines, fluorescent lights, and numerous other heavy electrical machines.
Explanation of Internal Noise:-