TRANSMISSION IMPAIRNMENT

Transmission impairment means the signal at the beginning and end of the meduium are not same .

                   There are three  types of impairment usually occurs :

·      

•              Attenuation
• ·         Distortion
• ·         Noise

ATTENUATION:

 Attenuation means loss of signal strength when a signal transmit through a medium, then some of its energy is loss in the form of heat.

                       To compensate for this loss, Amplifier are used to amplify the signal strength.

The decibel(dB) is used to measure the strength of signal at two difference points .If the signal is attenuated the dB is negative and if the signal is Amplified Then dB is  positive.

dB =10log₁₀(p2/p1)

Where p1 and p2 are the process of signal at point 1 and point 2.

 DISTORTION:

Distortion means that the signal changes its form or shape .Distortion occurs in a composite signal, made up of different frequencies. Each signal component has its own propagation speed through a medium and its own delay in arriving at the final destination.

Fig showing signal distortion

 NOISE :

  Noise is aunwanted signal which corrupt the signal.

There are several types of noise such as :-

 Thermal Noise :-  The random motion of electrons in a wirew that created an extra signal not originally sent by the transmitter.

 Induced Noise :-  It comes from sources , Such as motors & appliances. These devices act as a sending antenna & the Transmission medium acts as the receiving antenna.

 Cross Talk :- It is the effect of one of the wire on the other where one wire acts as a sending antenna and the other as receiving antenna.

Impulse Noise :- It is a spike that come from power lines , lighting etc.

NOTE:- THE SIGNAL TO NOISE RATIO IS EXPRESSED AS POWER RATIO , NOT IN DECIBELS

For Example – 30 dB is a power ratio of 10^30/10=10³=1000.