NOISE IN ANALOG COMMUNICATION SYSTEMS

INTRODUCTION:
In any communication system, during the transmission of the signal or while receiving the signal, some unwanted signal gets introduced into the communication, making it unpleasant for the receiver, and questioning the quality of the communication. Such a disturbance is called as Noise.

Most common examples of noise are −
 Hiss sound in radio receivers

 Buzz sound amidst of telephone conversations

 Flicker in television receivers, etc

TYPES OF NOISE:
The classification of noise is done depending on the type of the source, the effect it shows or the relation it has with the receiver, etc. There are two main ways in which noise is produced. One is through some external source while the other is created by an internal source, within the receiver section.
External Source:
This noise is produced by the external sources, which may occur in the medium or channel of communication usually. This noise cannot be completely eliminated. The best way is to avoid the noise from affecting the signal.

Most common examples of this type of noise are
 Atmospheric noise (due to irregularities in the atmosphere).  Extra-terrestrial noise, such as solar noise and cosmic noise.  Industrial noise.
Internal Source:
This noise is produced by the receiver components while functioning. The components in the circuits, due to continuous functioning, may produce few types of noise. This noise is quantifiable. A proper receiver design may lower the effect of this internal noise.
Examples:
Most common examples of this type of noise are
 Thermal agitation noise (Johnson noise or Electrical noise)  Shot noise (due to the random movement of electrons and holes)  Transit-time noise (during transition)  Miscellaneous noise is another type of noise which includes flicker, resistance effect and mixer generated noise, etc.
Effects of Noise:
Noise is an inconvenient feature, which affects the system performance. Following are the effects of noise.
Noise limits the operating range of the systems:
Noise indirectly places a limit on the weakest signal that can be amplified by an amplifier. The oscillator in the mixer circuit may limit its frequency because of noise. A system’s operation depends on the operation of its circuits. Noise limits the smallest signal that a receiver is capable of processing.
Noise affects the sensitivity of receivers:
Sensitivity is the minimum amount of input signal necessary to obtain the specified quality output. Noise affects the sensitivity of a receiver system, which eventually affects the output.

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