Noise and types of Noise

2. NOISE
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6.  Noise is unwanted electric energy that enters the communication
system via the communication medium and interferes with the
transmitted message.
 Noise may come from the atmosphere as well from the electrical
interference created by the manufactured equipment.
 In some cases it is also produced in the receiver.

7. Noise in Communication Systems
 Noise is an error or undesired random disturbance of a
useful information signal in a communication channel.
 It is one of the more serious problem in electronics
communication.
 It can not be completely eliminated.

8. Types of Noise
 Thermal noise :- (Thermal, Johnson or Nyquist noise) is
unavoidable, and generated by the random thermal motion
of electrons, inside an electrical conductor, which happens
regardless of any applied voltage.
 Its power density is nearly equal throughout the frequency
spectrum.
 Vn = sqrt (4 k T del f Rl)

9. Shot Noise
 Shot noise in electronic devices results from unavoidable
random statistical fluctuations of the electric current when
the charge carriers traverse a gap.
 The current is a flow of discrete charges, and the fluctuation
in the arrivals of those charges creates shot noise.
 It is expressed by Schottky formula
In = sqrt ( 2 I q del B)

10. Transit-time noise
 If the time taken by the electrons from traveling from
emitter to collector becomes equal to the period of the
signal being amplified.
 At frequencies above VHF and beyond, transit-time effect
takes place.
 Noise input admittance of the transistor increases.
 From the frequency at which this effect becomes significant
it goes on increasing with frequency and quickly dominates
over other terms.

11. External Noise
 Crosstalk :- This is unwanted coupling of signals. This
coupling occurs with the nearest cables used for other
transmissions.
 Atmospheric noise (static noise) :-This noise is also called
static noise. It is the natural source of disturbance caused
by lightning discharge of in thunderstorm and the
natural(electrical) disturbances occurring in nature.

12.  Industrial noise :- Sources such as automobiles, aircraft, ignition
electric motors, High voltage wires and fluorescent lamps cause
industrial noise. These noises are produced by the discharge
present in all these operations.
 Solar noise :- Noise that originates from the Sun. Under normal
conditions there is constant radiation from the Sun due to its
high temperature. Electrical disturbances such as corona
discharges, as well as sunspots can produce additional noise.

13. Cosmic noise
 Distant stars generate noise called cosmic noise.
 While these stars are too far away to individually affect
terrestrial communications systems, their large number leads to
appreciable collective effects.
 Cosmic noise has been observed in a range from 8 MHz to 1.43 GHz.

14. Reference
 Communication Electronics by frenzel
 https://en.wikipedia.org/wiki/Noisetypes