Noise may be defined as an unwanted form of energy which tends to interfere with the proper reception and reproduction of transmitted signal.
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There are mainly two ways of classifying the noise as under. 1. External Noise 2. Internal Noise
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The noise created outside the receiver is called External noise. The external noise con’t be analysed quantitatively that’s why it cannot be controlled.
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External Noise can be classified as 1. Atmospheric Noise 2. Extraterrestrial Noise 3. Industrial Noise
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Atmospheric Noise which is also called Static, is produced by lightning discharges in thunderstorm.
(a) Solar Noise : Solar noise is produced by the radiations emitting from sun because sun is very large body at very high temp. over 6000 °C.
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Industrial Noise ranges between 1 to 60 MHz and occurs in urban, suburban & industrial areas.
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Internal noise is that type of noise which generated internally the circuit or within the system or receiver. Internal noise are further categorized into following types: 1. Thermal Noise 2. Shot Noise 3. Flicker Noise 4. Burst Noise
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The thermal noise or the white noise which is generator in a resistor or the resistive Component of the circuit.
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This type of noise is caused by shot effect in all amplifying devices and active devices
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This type of noise is observed below few KHz frequency. Its spectral density denser increases with decreases in freq. Thus known as 1/f noise.
It consist of sudden step like transition between two or more discrete voltage or current levels, order of Several hundred microvolt. Current Last from several ms. to sec.