From the examples of communication discussed so far, now we can prepare the model of basic communication system. We know that for any communication to take place, three things are essential. They are,
- Transmitter (talker)
- Receiver (listener) and
- Channel or transmission medium.
The above three things are present in any communication system. Whenever two people are talking with each other, it becomes a communication system. In that case the voice signal is exchanged and the transmission medium is air. Fig shows the block diagram of basic communication system.
As shown in the figure, the source generates the message to be transmitted. The transmitter or talker sends that message over the transmission channel. The transmission channel can be the medium such as electric conductors, air or light (in case of optical fibre). The receiver or listener receives the message from transmission channel. It is then given to the destination by the receiver. During the transmission over the channel, the message is distorted and it becomes noisy.
What is the necessity of transmitter and receiver? Why source does not speak to destination directly?
This question is obvious. Source cannot speak to destination directly. For example consider a very simple example of television system. The programs are generated by shooting the objects through camera and they are stored on the video tape. Thus the program to be broadcasted is stored on the video tape initially.
This means the source of information is “Video tape”. The people watch this program on television. This means the destination of the program is the ‘people’. But the people (destination) cannot watch the program recorded on the video tape (source) directly. The tape is broadcasted on some TV channel by the TV broadcasting station or satellite. The Television set then receives this channel and people can watch the program on their TV set. Thus for the signal to be transmitted over long distance, the TV broadcasting station is essential. And to receive the signals which are present in the air, TV set is essential. In this communication system, the TV broadcasting station is the transmitter and TV set is the receiver. Thus we can say that,
The transmitter is required to make the signal suitable for conduction over the channel. And the receiver is required to convert the signal from transmission channel and make suitable for destination.