Sources of Noise
We can define Electrical noise as any undesirable electrical energy that falls within the passband of the signal.
Noise can be broadly divided into two categories, such as :
- correlated noise
- uncorrelated noise
Correlation implies a relationship between the signal and the noise. Therefore, correlated noise exists only when a signal is present.
Uncorrelated noise, on the other hand, is present all the time whether there is a signal or not.
Uncorrelated noise can be further subdivided into two general categories:
The noise can arise from different types of sources.
The sources of noise can be classified into the following categories:
1. Natural sources
2. Man-made sources
3. Fundamental sources (Internal sources)
1. Natural sources of noise
The natural phenomena that give rise to noise are electronic storms, solar flares and radiation in space.
For example , the noise received by the receiving antenna from the natural sources can only be reduced by repositioning the antenna.
The noise originating from the sun and the outer space is known as Extraterrestrial Noise.
The extraterrestrial noise can be sub-divided into two groups:
(a) Solar noise
(b) Cosmic noise
Our sun being a large body at very high temperatures radiates a lot of noise.
The temperature changes follow a cycle of 11 years, therefore, the periods of great electrical disturbances also repeats after every 11 years.
The cosmic noise comes from the stars. This is identical to the noise radiated by sun because stars also are large hot bodies. The noise is called as black body noise and it is distributed uniformly over the entire sky.
We also receive noise from the center of our galaxy, other galaxies and other virtual point sources such as Quasars and Pulsars.
2. Man-made sources of noise (Industrial noise)
The man-made noise is generated due to the make and break process in a current carrying circuit.
The examples are the electrical motors, welding machines, ignition system of the automobiles thyristorised high current circuits, fluorescent lights, switching gears etc.
3. Fundamental or internal sources of noise
The fundamental sources of noise are within the electronic equipment.
They are called fundamental sources because they are the integral part of the physical nature of the material used for making electronic components.
This type of noise follows certain rules. Hence, it can be eliminated by properly designing the electronic circuits and equipments.