BASIC TERMINOLOGY USED IN ELECTRONIC communication

BASIC TERMINOLOGY USED IN ELECTRONIC

COMMUNICATION SYSTEMS

By now, we have become familiar with some terms like information source,

transmitter, receiver, channel, noise, etc. It would be easy to understand

the principles underlying any communication, if we get ourselves

acquainted with the following basic terminology.

 (i) Transducer: Any device that converts one form of

energy into another can be termed as a transducer.

In electronic communication systems, we usually

come across devices that have either their inputs

or outputs in the electrical form. An electrical

transducer may be defined as a device that converts

some physical variable (pressure, displacement,

force, temperature, etc) into corresponding

variations in the electrical signal at its output.

(ii) Signal: Information converted in electrical form

and suitable for transmission is called a signal.

Signals can be either analog or digital. Analog

signals are continuous variations of voltage or

current. They are essentially single-valued

functions of time. Sine wave is a fundamental

analog signal. All other analog signals can be fully

understood in terms of their sine wave components.

Sound and picture signals in TV are analog in

nature. Digital signals are those which can take

only discrete stepwise values. Binary system that

is extensively used in digital electronics employs

just two levels of a signal. ‘0’ corresponds to a low

level and ‘1’ corresponds to a high level of voltage/

current. There are several coding schemes useful

for digital communication. They employ suitable

combinations of number systems such as the

binary coded decimal (BCD)*. American Standard

Code for Information Interchange (ASCII)** is a

universally popular digital code to represent

numbers, letters and certain characters.

(iii) Noise: Noise refers to the unwanted signals that

tend to disturb the transmission and processing

of message signals in a communication system.

The source generating the noise may be located

inside or outside the system.

(iv) Transmitter: A transmitter processes the incoming

message signal so as to make it suitable for

transmission through a channel and subsequent

reception.

(v) Receiver: A receiver extracts the desired message

signals from the received signals at the channel

output.

(vi) Attenuation: The loss of strength of a signal while

propagating through a medium is known as

attenuation.

* In BCD, a digit is usually represented by four binary (0 or 1) bits. For example

the numbers 0, 1, 2, 3, 4 in the decimal system are written as 0000, 0001, 0010,

0011 and 0100. 1000 would represent eight.

** It is a character encoding in terms of numbers based on English alphabet since

the computer can only understand numbers . Jagadis Chandra Bose

(1858 – 1937) He

developed an apparatus

for generating ultrashort

electro-magnetic waves

and studied their quasioptical

properties. He

was said to be the first to

employ a semiconductor

like galena as a selfrecovering

detector of

electromagnetic waves.

Bose published three

papers in the British

magazine, ‘The

Electrician’ of 27 Dec.

1895. His invention was

published in the

‘Proceedings of The Royal

Society’ on 27 April 1899

over two years before

Marconi’s first wireless

communication on 13

December 1901. Bose

also invented highly

sensitive instruments for

the detection of minute

responses by living

organisms to external

stimulii and established

parallelism between

animal and plant

tissues.

 (vii) Amplification: It is the process of increasing the amplitude (and

consequently the strength) of a signal using an electronic circuit

called the amplifier Amplification is

necessary to compensate for the attenuation of the signal in

communication systems. The energy needed for additional signal

strength is obtained from a DC power source. Amplification is

done at a place between the source and the destination wherever

signal strength becomes weaker than the required strength.

(viii) Range: It is the largest distance between a source and a destination

up to which the signal is received with sufficient strength.

(ix) Bandwidth: Bandwidth refers to the frequency range over which

an equipment operates or the portion of the spectrum occupied

by the signal.

(x) Modulation: The original low frequency message/information

signal cannot be transmitted to long distances because of

reasons. 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. As

will be explained later, there are several types of modulation,

abbreviated as AM, FM and PM.

(xi) Demodulation: The process of retrieval of information from the

carrier wave at the receiver is termed demodulation. This is the

reverse process of modulation.

(xii) Repeater: A repeater is a combination of a receiver and a

transmitter. A repeater, picks up the signal from the transmitter,

amplifies and retransmits it to the receiver sometimes with a

change in carrier frequency.