Scribd
Upload
34 views12 pages

Communication Systems:-A System Which Transmits Information

This document discusses communication systems and modulation. It provides: 1) A definition of communication systems as systems that transmit information from one point to another, and modulation as changing characteristics of a carrier wave like amplitude, frequency, or phase according to the signal. 2) The three main types of modulation are amplitude modulation, frequency modulation, and phase modulation. 3) Modulation is needed for practical reasons like allowing longer antenna lengths for transmission, operating over larger ranges, enabling wireless communication, facilitating frequency assignment and multiplexing, and reducing noise and interference.

Uploaded by

SRI KARTHIK
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PPTX, PDF, TXT or read online on Scribd
34 views12 pages

Communication Systems:-A System Which Transmits Information

This document discusses communication systems and modulation. It provides: 1) A definition of communication systems as systems that transmit information from one point to another, and modulation as changing characteristics of a carrier wave like amplitude, frequency, or phase according to the signal. 2) The three main types of modulation are amplitude modulation, frequency modulation, and phase modulation. 3) Modulation is needed for practical reasons like allowing longer antenna lengths for transmission, operating over larger ranges, enabling wireless communication, facilitating frequency assignment and multiplexing, and reducing noise and interference.

Uploaded by

SRI KARTHIK
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PPTX, PDF, TXT or read online on Scribd
You are on page 1/ 12

Unit - 2

COMMUNICATION SYSTEMS

communication systems:- A system which transmits information


from one point another point is known
as communication system.
communication system block diagram
Modulation
“The process of changing some characteristic (e.g. amplitude, frequency
or phase) of a carrier Wave in accordance with the intensity of the signal
is known as modulation”.

Types of Modulation:-
There are three basic types of modulation, namely ;
(i) Amplitude modulation
(ii) Frequency modulation
(iii) Phase modulation
Why Modulation needed?
1) Practical antenna length:-
Ex- Audio frequencies range from 20 Hz to 20 kHz, therefore, if they are transmitted directly
into space, the length of the transmitting antenna required would be extremely large.

For instance, to radiate a frequency of 20 kHz directly into space, we would need an antenna
3×108
length of = 15,000meters. This is too long antenna to be constructed practically. If a
20×103
carrier wave say of 1000 kHz is used to carry the signal, we need an antenna length of
300meters only and this size can be easily constructed.

The length of antenna (in air) can be calculated using,


𝐶
𝜆=
𝑓
Where, C = speed of light = 3 × 108 m/s
f = frequency in Hz.
2) Operating range:-
The energy of a wave depends upon its frequency. The greater the frequency of the wave, the
greater the energy possessed by it. As the audio signal frequencies are small, therefore, these
cannot be transmitted over large distances if radiated directly into space. Thus modulating a
high frequency carrier wave with audio signal and permit the transmission to occur at this
high frequency (i.e. carrier frequency).

3) Wireless communication:-
One desirable feature of radio transmission is that it should be carried without wires i.e.
radiated into space. At audio frequencies, radiation is not practicable because the efficiency
of radiation is poor. However, efficient radiation of electrical energy is possible at high
frequencies > 20 kHz.

4) Modulation for ease of radiation

5) Modulation allows frequency assignment and multiplexing

6) Modulation reduces the noise and interference


1) Amplitude Modulation (AM)
When the amplitude of high frequency carrier wave is changed in accordance with the
intensity of the signal, it is called amplitude modulation.
In amplitude modulation, only the amplitude of the carrier wave is changed in accordance
with the intensity of the signal and the frequency of the modulated wave remains the same
i.e. carrier frequency.
2) Frequency Modulation (FM)
When the frequency of carrier wave is changed in accordance with the intensity of the signal,
it is called frequency modulation (FM). In frequency modulation, only the frequency of the
carrier wave is changed in accordance with the signal and the amplitude of the modulated
wave remains the same i.e. carrier wave amplitude.
3) Phase modulation (PM)
When the phase of carrier wave is changed in accordance with the intensity of the signal, it is
called phase modulation
AM & FM Combine Animation

You might also like