Communication system

Wednesday, May 3, 2023 1Imran

Communication is the act of transmission of information.

Every communication system has three essential elements-transmitter, transmission medium / channel and receiver.

COMMUNICATION SYSTEMS


The purpose of transmitter is to convert the message signal produced by source of information into a form suitable for transmission through the channel.

The transmission channel is the medium that bridges the distance from source to destination.

The receiver reconstructs the original message/ data after its propagation through the communication channel.

An Antenna is a metallic structure used to radiate or receive electromagnetic waves. Various types of antennas are used in the field of communication.


Short dipole Simple dipole Dish-type antenna antenna antennaBasic terminology used in electronic communication system:Transducer:- Any device that converts one form of

energy into another can be termed as a transducer.Signal:- Information converted into electrical form

and suitable for transmission is called a signal.


Noise:- Noise refers to the unwanted signals that tend to disturb the transmission and processing of message signals in a communication system.

Transmitter:- A transmitter processes the incoming message signal so as to make it suitable for transmission through a channel and subsequent reception.

Receiver:- A receiver extracts the desired message signals from the received signals at the channel output.

Attenuation:- The loss of strength of a signal while propagating through a medium is known as attenuation.


Amplification:- It is the process of increasing the amplitude of a signal using an electronic circuit called the amplifier.

Range:- It is the largest distance between a source of signal and destination up to which the signal is received with sufficient strength.

Bandwidth:- Bandwidth refers to the frequency range over which an equipment operates or the portion of the spectrum occupied by the signal.

Modulation:- The original low frequency message cannot be transmitted to long distances. Therefore, at the transmitter, information contained in the low frequency message signal is superimposed on a high frequency wave, which acts as a carrier of the information. This process is known as modulation.


Demodulation:- The process of retrieval of information from the carrier wave at receiver is termed demodulation. This is the reverse process of modulation.

Repeater:- A repeater is a combination of a receiver and a transmitter.

Use of repeater station to increase the range of communication.


Message:- A message signal is a single-valued function of time which contains or conveys information.

a) Analog signal:- An analog signal is one in which the voltage (or current) varies continuously with time.

b) Digital signal:- A digital signal is one which can have only two levels of voltage (or current).


Communication channels:- For establishing a communication between a transmitting and receiving station, we need a physical medium through which signals may propagate. This is referred to as communication channel. Principally there are two types of communications.

i. Line communication:- It is to launch and to guide the signals along a conducting physical path (or line) to the receiver.

ii. Space communication:- It is the method to transmit the signal freely in space by using an antenna and receive at the other end by intercepting the signal with the help of another antenna.


Ground Wave Propagation (or surface wave propagation):- The AM radiowaves which propagate from one point to another following the surface of Earth are known as ground waves or surface waves. This type of propagation is called ground wave propagation or surface wave propagation.


Sky wave propagation or ionospheric propagation:- Sky waves are the AM radio waves which are received after being reflected from the ionosphere. The propagation of radiowave signals from one point to another via reflection from ionosphere is known as sky wave propagation.


Important terms used in the study of sky wave propagation:-

• Virtual height:- As the wave is refracted, it is bent down gradually rather than sharply. However, below the ionised layer, the incident and refracted rays follow paths that are exactly the same as they would have been if reflection had taken place from a surface located at a greater height, called the virtual height of this layer.


• Critical Frequency:- The critical frequency for a given layer is the highest frequency that will be returned down to earth by that layer after having been beamed straight up at it. The critical frequency ranges approximately from 5 MHz to 10 MHz .

• Maximum usable frequency:- Maximum usable frequency is that highest frequency of radio waves which when beamed, at some angle with the normal, towards the ionosphere gets reflected and returns to the earth ‘or’ it is the highest frequency that can be used for sky wave communication between two given points on earth.


• Optimum Working frequency:- It is the frequency normally used for ionosphere transmission. OWF is generally 15% of MUF.

• Skip distance:- The skip distance is the shortest distance from a transmitter, measured along the surface of the Earth, at which a sky wave of fixed frequency will be returned to Earth.


Different types of modulation:- Amplitude modulation:- When the

amplitude of high frequency carrier wave is changed in accordance with intensity of the signal, it is called amplitude modulation.


Frequency modulation:- In frequency modulation, the frequency of the carrier wave is modified in accordance with the amplitude of the modulating wave.

Communication system

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