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

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

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

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

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

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

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

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