External Noise :
- It is external to the communication equipment like radio receiver ,television ,telephone ,etc…
- External nose are uncontrollable at a given geographical location.
- External noise can be further classified into three types as follows.
- Atmospheric Noise
- Extraterrestrial Noise
- Solar Noise
a.Atmospheric Noise :
- Atmospheric noise is radio noise caused by natural atmospheric processes, primarily lightning discharges in thunderstorm.
- Atmospheric noise is commonly called static electricity noise.
- Atmospheric noise has wide range of frequency hence it has large bandwidth.
- Amplitude of this noise is inversely proportional to the frequency.
b.Extra-terrestrial Noise :
- Noise consists of electrical signals that originate from outside Earth’s atmosphere.
- It is sometimes called as deep space noise.
- It has frequency range from 8MHz to 1.43GHz.
- Extraterrestrial nose can be divided into two categories.
- Solar Noise
- Cosmic Noise
Solar Noise :
- Source of this noise is sun.
- This noise is generated due to constant radiation from sun at high temperature.
- Spectrum of this radiation is broad and interferes with communication channels.
- Magnitude of this noise changes with time.
Cosmic Noise :
- Source of this noise is stars.
- These stars are at large distance and they have also high temperature due to which they are radiating cosmic noise.
- Cosmic noise uniformly distributed over entire sky and uniformly distributed over frequency spectrum
- If we receive it from galaxy, it is known as galactic noise.
c.Industrial Noise :
- Source of industrial noise are automobile-air craft ignition,electric motor-switch gears, fluorescent light,etc.. a
- It is man-made noise.