• Attenuation: When a signal travels through a medium, it loses some of its energy due to resistance of the medium. This loss of energy is called the Attenuation. This is the reason why a wire carrying electric signals gets warm. Some of the electrical energy in the signal is converted to heat. To overcome this problem, amplifiers are used to amplify the signal. Unit of the decibel is used to FIND out if a signal has lost or gained strength. The decibel (DB) measures the relative strengths of two signals or one signal at two different points. If decibel is negative then a signal is attenuated and if the positive signal is amplified. 

FORMULA: Where PI and P2 are the variable and the powers of a signal at points 1 and 2, respectively. 

•  Distortion: When the signal travels through the medium from one point to another it may chance to change the form or shape of the signal. It is called distortion. Distortion can occur in a composite signal made up of different frequencies. Each signal component has its own propagation speed through a traveling medium and, therefore, its own delay in reaching the final destination. Means signal components at the receiver have phases different from what they had at the sender.
•  NOISE: The third cause of impairment is Noise. Following types of noise are possible.

1.  Thermal noise.
2.  Induced noise.
3.  Crosstalk noise.
4.  Impulse noise.

This noise may corrupt the signal.Thermal noise is produced due to the random motion of electrons in a wire which creates an extra signal not originally sent by the transmitter. Induced noise comes from sources such as motors and other electronic appliances. These devices act as a sending antenna, and the transmission medium ACTS as the receiving antenna. Crosstalk is the effect of one wire on the other. Impulse noise comes from power lines, lightning etc.

Formula: Where PI and P2 are the variable and the powers of a signal at points 1 and 2, respectively. 

This noise may corrupt the signal.Thermal noise is produced due to the random motion of electrons in a wire which creates an extra signal not originally sent by the transmitter. Induced noise comes from sources such as motors and other electronic appliances. These devices act as a sending antenna, and the transmission medium acts as the receiving antenna. Crosstalk is the effect of one wire on the other. Impulse noise comes from power lines, lightning etc.