1_Amplitude_modulation

Information about 1_Amplitude_modulation

Published on August 1, 2014

Author: superman28

Source: authorstream.com

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PowerPoint Presentation: PRINCIPLES OF COMMUNICATION BASICS OF COMMUNICATION AMPLITUDE MODULATION Created by C. Mani, Principal, K V No.1, AFS, Jalahalli West, Bangalore PowerPoint Presentation: BASICS OF COMMUNICATION 1. Communication: Processing, sending and receiving of information 2. Information: Intelligence, signal, data or any measurable physical quantity 3. Basic Communication System: Source of information Transmitter Link Receiver Destination i) Speech ii) Pictures iii) Words iv) Codes v) Symbols vi) Commands vii) Data i) Oscillators ii) Amplifiers iii) Filters iv) Antenna i) Wire Links ii) Wireless iii) Optic Fibres i) Radio ii) TV iii) Computer iv) Telephone v) Teleprinter vi) Telegraph vii) Fax viii) Internet PowerPoint Presentation: 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 Satellite communication Optic fibre communication PowerPoint Presentation: Analogue signal A continuous signal value which at any instant lies within the range of a maximum and a minimum value. A discontinuous signal value which appears in steps in pre-determined levels rather than having the continuous change. Digital signal 0 t V 1 0 1 0 1 0 1 0 1 T/4 T/2 3T/4 T 5T/4 3T/2 7T/4 2T t 0 π 2 π 3 π 4 π π /2 3 π /2 5 π /2 7 π /2 θ = ω t E , I E 0 I 0 E = E 0 sin ω t I = I 0 sin ω t PowerPoint Presentation: MODULATION: Types of Modulation : Amplitude Modulation Frequency Modulation Pulse Modulation Phase 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 A.F. Signal Amp. Modulated Signal H.F. Signal Oscillator PowerPoint Presentation: AMPLITUDE MODULATION (AM): e m = E m sin  m t e c = E c sin  c t e = (E c + E m sin  m t) sin  c t Modulation Index (m a )= k a E m /E c If k a =1, then m a = E m /E c e = E c sin  c t + (m a E c /2) cos ( c -  m )t - (m a E c /2) cos ( c +  m )t (Courtesy: Internet) PowerPoint Presentation: The Amplitude Modulated wave is the summation of three sinusoidal waves with the frequencies  c ,  c - m and  c + m namely Original frequency, Lower Side Band frequency and Upper Side Band frequency respectively. The Bandwidth required for AM, BW = 2  m 3. The amplitude E c of the unmodulated carrier wave is made proportional to the instantaneous voltage (e m = E m sin  m t) of the modulating wave. Voltage Amplitude  c - m Frequency Inferences from equation for e:  c  c + m (Courtesy: Internet) PowerPoint Presentation: Significance of Modulation Index: m a E c = k a E m E min E max e 0 E max = E c + m a E c E min = E c - m a E c E max - E min E max + E min m a = Generally, 0 < m a < 1 AF signal m a = 0 (No modulation) m a = 0.5 or 50% On manipulating, we get m a = 1 or 100% m a > 1 or 100% E c PowerPoint Presentation: Power Relation in the AM wave: If the modulated wave is applied to a resistor of resistance R (say antenna circuit), then the r.m.s. power dissipated in the form of heat is, P r.m.s = (1/R) E c /22 2 + m a E c /22 2 + m a E c /22 2  P rms = (E c 2 /2R) 1 + (m a 2 /2) = P c 1 + (m a 2 /2) (where P c is power dissipated by unmodulated carrier wave) If m a = 1, then P rms  P max and P max = 3 P c /2 Similarly, Power carried by both side bands P SB = P rms / 3 which is wasted. PowerPoint Presentation: 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. Advantages: END

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