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.
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