1. Elements of a Communication System

Chapter 15: Communication System

Elements of a Communication System

Communication Systems

The communication system is a system which describes the information exchange between two points. The process of transmission and reception of information is called communication.

Types Of Communication Systems

Depending on Signal specification or technology, the communication system is classified as follows

• Analog

Analog technology communicates data as electronic signals of varying frequency or amplitude. Broadcast and telephone transmission are common examples of Analog technology.

• Digital

In digital technology, the data are generated and processed in two states: High (represented as 1) and Low (represented as 0). Digital technology stores and transmits data in the form of 1s and 0s.

BASIC TERMINOLOGY USED IN ELECTRONIC COMMUNICATION SYSTEMS

The definitions of the terms used in the communication system are discussed below.

Information

Message or information is the entity that is to be transmitted. It can be in the form of audio, video, temperature, picture, pressure, etc.

Signal

The single-valued function of time that carries the information. The information is converted into an electrical form for transmission.

Transducer

A device or an arrangement that converts one form of energy to the other. Example: Microphone – converts audio signals into electrical signals. Photodetector – converts light signals into electrical signals.

Amplifier

The electronic circuit or device that increases the amplitude or the strength of the transmitted signal is called an amplifier.

Modulator

As the original message signal cannot be transmitted over a large distance because of their low frequency and amplitude, they are superimposed with high frequency and amplitude wave called carrier wave.

Transmitter

It is the arrangement that processes the message signal into a suitable form for transmission and subsequently reception.

Channel

A channel refers to a physical medium such as wire, cables, space through which the signal is passed from the transmitter to the receiver.

Noise

Noise is one of the channel imperfection or impairment in the received signal at the destination. There are external and internal sources that cause noise.

BANDWIDTH OF SIGNALS

Bandwidth refers to the frequency range over which an equipment operates or the portion of the spectrum occupied by the signal. Different types of signals (music, picture or computer data) require different bandwidth.

• Speech signal requires a bandwidth of 2800 Hz (3100 Hz – 300 Hz) for telephonic conversation.
• Video signals for transmission of pictures require about 4.2 MHz of bandwidth.
• A TV signal contains both voice and picture and is usually allocated 6 MHz of bandwidth for transmission.

Bandwidth of Transmission Medium

Different types of transmission media offer different bandwidths.

• The commonly used transmission media are wire, free space and fiber optic cable.
• Coaxial cable offers a bandwidth of approximately 750 MHz. Such cables are normally operated below 18 GHz.