Wave, Wave properties, Elecromagnetic energy, propagation of Elecromagnetic waves,Signal phase, Impulse noise, Cross talk, Mechanical Waves,Thermal noise,Induced noise, Peak amplitude,Period and Frequency, Transmission Implements, Signal Attenuaton, Distortion, Wave free space loss, Signal noise,Analog and Digital Signal,Refraction,Properties of Light Signals,Properties of Electrical Signals,Types of Signals

Waves and Signals
Waves:
    Wave is defined as a disturbance or vibration that travels through a medium or vacuum from one to another location.This disturbance carries energy from one location to another. We can also describe wave as the transfer of energy from one location to another. Based on their mode of travel, waves are categorized into:

1. Electromagnetic Waves
     An Electromagnetic wave can travel through vacuum and does
   not require material medium for transmission. 

2. Mechanical Waves
   It can not travel through vacuum and needs a material medium
   for transmission. Modern communication systems use
   electromagnetic waves to transfer information.

Wave Properties:
   Waves have properties that affect the information carried by them.The various properties of a wave are -
  1.         Peak Amplitude
  2.         Period
  3.         Frequency
  4.         Wavelength
  5.         Phase
  6.         Speed of propagation.
Peak Amplitude: 
    The peak amplitude of a wave is the value of its highest intensity, proportional to the energy it carries.Neither the wavelength nor frequency of a wave depends on the amplitude.
 
Figure : Peak Amplitude

Period and Frequency:
      Period refers to the amount of time, in seconds, a wave needs to complete one cycle. The period of a waveis measured in seconds.The frequency of a wave refers to the number of periods in one second. Its unit is Hertz (Hz).
 Figure : Period frequency and wavelength of a wave


Phase:
     Position of a waveform relative to time to zero is called phase. It describes the amount of forward or backward shift along the time axis which indicates the status of the first cycle. Phase is calculated in degree or radian. The position of the waveform relative to time zero is called phase.

Electromagnetic Energy:
  Electrical energy or electromagnetic energy is a form of energy
  present in any electric field or magnetic field, or in any volume
  containing electromagnetic radiation.

Propagation of EM Waves:

 The two types of electromagnetic waves that are used to carry

 information are-


  1. Radio waves

  2. Light waves


  Based on the characteristics of propagation, radio waves are 

   divided into three categories -


  1. Ground waves

  2. Sky waves

  3. Line-of-sight waves

Transmission Impairments:

The four types of impairments are:

1. Attenuation.

2. Distortion.

3. Free space loss.

4. Noise.

Attenuation:  
Attenuation is the loss of energy or strength of a wave with distance
over any transmission medium or vacuum.

Figure : Attenuation

Distortion:
    Distortion refers to a change in the from or shape of a wave. A wave may have different frequency components may have different speed through the medium. This component may also different energies, and thus different attenuation. The attenuation typically is greater for higher frequency components, and causes additional distortion, known as attenuation distortion.
 
Figure : Distortion
Free space loss: 
The electromagnetic waves traveling through the atmosphere get 
dispersed with the distance traveled. The waves spread over a large 
area in the free space
Noise: 
Unwanted waves modify the waves carrying information during 
transmission. These unwanted waves are referred to as noise. Noise 
is divided into the following categories -
  1. Thermal noise

  2. Induced  noise

  3. Cross talk

  4. Impulse noise


Note: The random motion of electrons in a medium produces 
          thermal noise; thermal noise is also known as   white noise or      Johnson noise.

Types of Signals: 
The three types of signals used in telecommunications are

  1. Electrical signals

  2. Light signals

  3. Electromagnetic signals other than light (or radio waves)

Properties of Electrical Signals: 
  1.        Bandwidth of an Electrical Signal.
  2.        Data Rate of an Electrical Signal.       

 Note:The absolute value of the difference between the lowest and    highest frequencies of a signal is called Bandwidth and the  range of that a signal spans from minimum to maximum is  called Spectrum.
Properties of Light Signals: 
      1.  Refraction     2.  Bandwidth   3.  Loss     4.  Data Rate
Refraction:

Figure : Bending of light ray
The two types of signals used in a telecommunication network are-
         1. Analog 
   2. Digital
Note: 1. Signal is the electrical representation of data. Signal and
              data both have analog and digital forms.
         2.  Analog signals take an infinite number of values in a range.         Digital signals take a limited number of values in a range.

Analog and Digital Signal:

 
Figure : (a) Analog signal (b) Digital signal