Mumbai University > Electronics Engineering > Sem4 > Fundamentals of Communication Engineering

Marks: 5M

Year: May 14

Noise

1. Noise is an unwanted electrical signal which gets added to the transmitted signal when it is travelling towards receiver.
2. Due to noise, the quality of the transmitted information will degrade. One added the noise cannot be separated out from the information
3. Hence noise is ab big problem in the communication systems
4. The noise can either be manmade or natural. The sources of natural voice are lightening or radiation from the sun and stars.
5. The main made noise includes the noise produced by electrical ignition systems of the automobiles, vending machines.
6. Even though the noise can be completely eliminated its effect can be reduced by using various techniques

Equivalent Noise Temperature

• The equivalent noise temperature of a system is defined as the temperature at which the noise resistor has to be maintained so that by connecting this resistor to the input of a noiseless version of the system, it will produce the same amount of noise power at the system output as that produced by the actual system.

• The noise at the input of the amplifier input is given by

  $$P_{na} = (F-1) k T_c B$$

  This is the noise contributed by the amplifier. This noise power can be alternatively represented by some fictitious temperature Teq such that

  $$K T_{eq} B = (F-1) k T_c B$$

  Thus the equivalent noise temperature of the amplifier is given by

  $$T_{eq} = (F-1) T_c$$

  This equation shows that Teq is just an alternative measre for F.