The system in which information can be sent and receive
from one place to other is called communication system.

Now a days three types of communication system are used:
(1)Electrical                                        (2)Electronic                (3)Optical

In every system of communication there are three important parts : (i)Transmission (ii)Communication Channel (iii)Receiver

(i)Transmitter :   The main function of a transmitter is to collect signal produced by source and to transmit it in suitable form to channel for sanding it to receiver. if the out put of a source is sound and so signal (sound signal).

Then it is converted into electrical signal by microphone (Transducer) before sending it. This is called information (message) signal. So conversion of main signal into message signal is main part of the process of transmitter.

(ii)Communication Channel : Communication Channel is a physical medium which connect transmitter and receiver i.e. It provides a path between transmitter and receiver by which signal is communicated .

Communication channel is also called medium link between transmitter and receiver.
The form of channel depends upon type of communication system. This can be a form of wire or cable between transmitter and receiver or can be wireless system.

When the signal to be transmitted propagates along the communication channel due to imperfection it is distorted and in the communication signal noise also get’s superpose so signal in distorted form is available.

(iii)Receiver : The main part of a receiver is to detect the signal and to rebuilt the received message and to convert it into main signal to be detected in orignal form.

So that the message can be send to receiving person. So main function of receiver is to receive the output of channel and to convert it into desirable signal i.e. to rebuilt it into main form.

Explanation : When a person wants to tell something to another person sitting near to him then he speaks something to tell him about something. The person who is speaking is the source of information and is a transmitter and sound waves are propagating in air medium (channel).

The sound waves are the signal which is communicated by our medium to other person who listens all signals. So Ears of the person who receives the sound are receiver. This is simplest form of communication system.

If the distance between source (Transmitter) and receiver is very large then signal gets weak before reaching to receiver i.e. to the listener. In this case the sound waves are converted into electrical signal and with the help of wires are communicated to long distance .

The part by sound waves are converted into electrical signal is called microphone (Transducer) converts electrical to sound signal. When it is not possible to have contact between transmitter and receiver with the help of wire or cables in that case main signal first is converted into electrical signal and with the help of antenna is sent in the space.

The free space acts as communication channel and the signal is received by the antenna of receiver at a large distance. The received signal with the help of transducer and amplifier is converted into main signal.  

  Modes of communications :

(aPoint to point communication : in this mode there is one transmitter and one receiver. In this the message sent by a person by a transmitting media or by communication is given to receiver. Example: Telephone system.

(bBroadcast : In this there only one transmitter and there many receiver by so many receivers. In this one transmitter.
broadcasts the information or message and it is received by so many receivers. Example : Radio and Television.


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