1. COMMUNICATION SYSTEM BASIC PRINCIPLES OF COMMUNICATION
MODULATION AND IT’S NECESSITY

2. Basics of communication
1.Communication: Processing, sending and receiving of information
2. Information: Intelligence, signal, data or any measurable physical quantity

3. Block Diagram of Communication System
i) Wire Links ii) Wireless (air or vaccum) iii) Optic Fibres
Source of information
Transmitter
Link or Transmitting Medium
i)Oscillators ii) Amplifiers
iii) Filters iv) Antenna
v) Transducer vi) Modulator
i) Speech
ii) Pictures
iii) Words
iv) Codes
v) Symbols
vi) Commands
vii) Data
viii) Audio
ix) Video Signals
Noise
Destination
(Human Being)
Receiver
Radio v) Teleprinter
TV vi) Telegraph
Computer vii) Fax
Telephone & Mobile viii) Internet

4. Forms of Communication Types of communication
1. Radio Broadcast
2. Television Broadcast
3. Telephony
4. Telegraphy
Radar
Sonar
Fax (Facsimile Telegraphy)
Teleprinting
Telemetering
Mobile Phones
Internet
Cable communication
Ground wave communication
Sky wave communication
Space Wave communication using Satellites
Optic fibre communication

5. Analogue signal Digital signal
A continuous signal value which can have any value lies within the range of a maximum and a minimum value.
A discontinuous signal which can have only certain values.
E = E0 sin ωt
E ,I
I = I0 sin ωt E0 I0 V 1 π 2π 3π 4π
π/2
3π/2
5π/2
7π/2
θ = ωt
T/4 T/2 3T/4 T 5T/4 3T/2 7T/4 2T t t

6. MODULATION
Modulation is the process of variation of some characteristic of a high frequency wave (carrier wave) in accordance with the instantaneous value of a modulating signal.
Modulator
Modulating signal
Carrier Waves (EM Waves)
Amp. Modulated Signal
Types of Modulation:
Amplitude Modulation
Frequency Modulation
Pulse Modulation
Phase Modulation
H.F. Signal Oscillator

7. AMPLITUDE MODULATION (AM) e m= Em sin mt
ec = Ec sin ct
e = (Ec + Em sin mt) sin ct
e = Ec sin ct + Em sin mt sin ct
Modulating Wave Equation
Carrier Wave Equation
Resultant Modulated Wave Equation
e = Ec sin ct + (mi Ec/2) cos (c - m)t - (miEc/2) cos (c + m)t
Ec = Carrier Wave Amplitude, Em = Modulating Wave Amplitude
m = Angular Frequency of Modulating Wave
c = Angular Frequency of Carrier Wave

8. Advantages
1. AM is an easier method of transmitting and receiving speech signals.
It requires simple and inexpensive receivers.
It is a fairly efficient system of modulation.
Drawbacks:
AM is more likely to suffer from noise.
Appreciable energy is contained by three components of AM wave. Sufficient energy can be saved by suppressing carrier wave and one of the side bands. This process makes the equipment complex.
3. Cost of such transmitters and receivers becomes practically more.
END