5.5.2 Commonly used terms in electronic communication system

Following terms are useful to understand any communication system:

1) Signal :-

The information converted into electrical form that is suitable for transmission is called a signal.

In a radio station, music and speech are converted into electrical form by a microphone for transmission into space.

This electrical form of sound is the signal.

A signal can be analog or digital

(a) Analog signal. (b) Digital signal.

(i) Analog signal:

A continuously varying signal (voltage or current) is called an analog signal.

Since a wave is a fundamental analog signal, sound and picture signals in TV are analog in nature.

(ii) Digital signal :

A signal (voltage or current) that can have only two discrete values is called a digital signal.

For example, a square wave is a digital signal.

It has two values viz, +5 V and 0 V.

2) Transmitter :-

A transmitter converts the signal produced by a source of information into a form suitable for transmission through a channel and subsequent reception.

3) Transducer :-

A device that converts one form of energy into another form of energy is called a transducer.

For example, a microphone converts sound energy into electrical energy.

Therefore, a microphone is a transducer.

Similarly, a loudspeaker is a transducer which converts electrical energy into sound energy.

4) Receiver :-

The receiver receives the message signal at the channel output, reconstructs it in recognizable form of the original message for delivering it to the user of information.

5) Noise :-

A random unwanted signal is called noise.

The source generating the noise may be located inside or outside the system.

Efforts should be made to minimise the noise level in a communication system.

6) Attenuation :-

The loss of strength of the signal while propagating through the channel is known as attenuation.

It occurs because the channel distorts, reflects and refracts the signals as it passes through it.

7) Amplification :-

Amplification is the process of raising the strength of a signal, using an electronic circuit called amplifier.

8) Range :-

The maximum (largest) distance between a source and a destination up to which the signal can be received with sufficient strength is termed as range.

9) Bandwidth :-

The bandwidth of an electronic circuit is the range of frequencies over which it operates efficiently.

10) Modulation :-

The signals in communication system (e.g. music, speech etc.) are low frequency signals and cannot be transmitted over large distances.

In order to transmit the signal to large distances, it is superimposed on a high frequency wave (called carrier wave).

This process is called modulation.

Modulation is done at the transmitter and is an important part of a communication system.

11) Demodulation :-

The process of regaining signal from a modulated wave is called demodulation.

This is the reverse process of modulation.

12) Repeater :-

It is a combination of a transmitter and a receiver.

The receiver receives the signal from the transmitter, amplifies it and transmits it to the next repeater.

Repeaters areused to increase the range of a communication system.