AC Project Report-AM GENERATION USING MATLAB PDF

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AM GENERATION USING MATLAB LAB PROJECT REPORT-ANALOG COMMUNICATIONS...

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“AM GENERATION USING MATLAB” ABSTRACT: Amplitude modulation (AM) is a one of the conventional modulation technique to transmit signals using a carrier wave. The amplitude or the strength of a high frequency carrier wave is changed in accordance with the amplitude of message signal. First of all lets get into the basics..  

Carrier signal (Sc) = Acsin(2πfct) Message signal (Sm) = Amsin(2πfmt)

Where,    

Ac – Amplitude of the carrier signal Am – Amplitude of the message signal fc – frequency of the carrier signal fm – frequency of the message signal

When the signal is amplitude modulated, the amplitude of the high frequency carrier is varied in accordance with the amplitude of message signal. 

Modulated Signal = (Ac+ Amsin(2 πfmt))*sin(2 πfct)

Modulation Index or Modulation Depth is the one of the most common term that used along with modulation techniques. Here in AM, it is the measure of amplitude variation surrounding an unmodulated carrier. It is the ratio of the amplitude of message signal to the amplitude of carrier signal.In terms of modulation index (m=Am/Ac) the equation of the modulated signal becomes, 

Modulated signal = (1+ msin(2 πfmt))*Acsin(2 πfct)

1.AIM OF PROJECT To Generate Amplitude Modulated Waveform using MATLAB SOFTWARE.

2.SOFTWARE USED: MATLAB Software.

3.BACKGROUND THEORY : A continuous-wave goes on continuously without any intervals and it is the baseband message signal, which contains the information. This wave has to be modulated.According to the standard definition, “The amplitude of the carrier signal varies in accordance with the instantaneous amplitude of the modulating signal.” Which means, the amplitude of the carrier signal containing no information varies as per the amplitude of the signal containing information, at each instant. The basic theory and equations behind amplitude modulation are relatively straightforward and can be handled using straightforward trigonometric calculations and manipulation.Essentially an amplitude modulated wave consists of a radio frequency carrier a sine wave at one frequency, typically in the radio frequency portion of the spectrum. A modulating wave, which in theory could be another sine wave, typically at a lower audio frequency is superimposed upon the carrier.The two signals are multiplied together and the theory shows how they interact to create the carrier and two sidebands.The equations for the simple example of the a single tone used for modulation can be expanded to show how the signal will appear of a typical sound consisting of many frequencies is used to modulated the carrier.

It is possible to look at the theory of the generation of an amplitude modulated signal in three steps: 1. Carrier signal 2. Modulating signal 3. Overall modulated signal for a single tone These steps will be covered in greater details below: 1. Carrier signal equations Looking at the theory, it is possible to describe the carrier in terms of a sine wave as follows: C(t) = C sin(ωc + φ)C(t) = C sin(ωc + φ)

Here C is the carrier Amplitude and wc is the carrier frequency, φ is the phase of the signal at the start of the reference time.Both C and φ can be omitted to simplify the equation by changing C to "1" and φ to "0". 2. Modulating signal equations The modulating waveform can either be a single tone. This can be represented by a cosine waveform, or the modulating waveform could be a wide variety of frequencies - these can be represented by a series of cosine waveforms added together in a linear fashion. For the initial look at how the signal is formed, it is easiest to look at the equation for a simple single tone waveform and then expand the concept to cover the more normal case. Take a single tone waveform: m(t) = M sin(ωm + φ)m(t) = M sin(ωm + φ) Where: M is the message Amplitude ,wm is the message frequency,φ is the phase of the signal at the start of the reference time.Both C and φ can be omitted to simplify the equation by changing C to "1" and φ to "0". It is worth noting that normally the modulating signal frequency is well below that of the carrier frequency. 3. Overall modulated signal The equation for the overall modulated signal is obtained by multiplying the carrier and the modulating signal together. y(t) = [A + m(t)].c(t)y(t) = [A + m(t)].c(t) The constant A is required as it represents the amplitude of the waveform. Substituting in the individual relationships for the carrier and modulating signal, the overall signal becomes: y(t) = [A + Mcos(ωmt+φ].sin(ωct)y(t) = [A + Mcos(ωmt+φ].sin(ωct) The trigonometry can then be expanded out to give an equation that includes the components of the signal: y(t) = A.sin(ωct)+A M2[sin((ωc+ωm)t+φ)]+A M2[sin((ωc−ωm)t−φ)]y(t) = A.sin(ωct)+A M2[sin((ωc+ωm)t+φ)]+A M2[sin((ωc-ωm)t-φ)]

The figure shows the modulating wave.It can be observed that the positive and negative peaks of the carrier wave, are interconnected with an imaginary line. This line helps recreating the exact shape of the modulating signal. This imaginary line on the carrier wave is called as Envelope. It is the same as that of the message signal.

4.WAVE FORMS

MATLAB CODE FOR AM Generation : %MATLAB CODE FOR GENERATION OF AM SIGNAL clc; close all; clear all; m = 1; Am = 5; %Amp. of modulating signal fa = 2000; %frequency of modulating signal Ta = 1/fa; t = 0:Ta/999:6*Ta; ym = Am*sin(2*pi*fa*t); figure(1)

subplot(3,1,1) plot(t,ym) title('Modulating Signal') %Carrier signal Ac = Am/m; fc = fa*10; Tc = 1/fc; yc = Ac*sin(2*pi*fc*t); subplot(3,1,2) plot(t,yc) grid on; title('Carrier Signal') %AM Modulation y = Ac + (1+m*sin(2*pi*fa*t)).*sin(2*pi*fc*t); subplot(3,1,3) plot(t,y) title('Amplitude Modulated Signal') grid on;

6. RESULTS: MATLAB OUTPUT WAVEFORMS

7. APPLICATIONS Amplitude modulation is used in a variety of applications. Even though it is not as widely used as it was in previous years in its basic format it can nevertheless still be found. Broadcast transmissions: AM is still widely used for broadcasting on the long, medium and short wave bands. It is simple to demodulate and this means that radio receivers capable of demodulating amplitude modulation are cheap and simple to manufacture. Nevertheless many people are moving to high quality forms of transmission like frequency modulation, FM or digital transmissions.  Air band radio: VHF transmissions for many airborne applications still use AM. . It is used for ground to air radio communications as well as two way radio links for ground staff as well.  Single sideband: Amplitude modulation in the form of single sideband is still used for HF radio links. Using a lower bandwidth and providing more effective use of the transmitted power this form of modulation is still used for many point to point HF links.  Quadrature amplitude modulation: AM is widely used for the transmission of data in everything from short range wireless links such as Wi-Fi to cellular telecommunications and much more. Effectively it is formed by having two carriers 90° out of phase. These form some of the main uses of amplitude modulation. However in its basic form, this form of modulation is being used less as a result of its inefficient use of both spectrum and power. 

8.CONCLUSION In amplitude modulation, the carrier frequency is constant, on the other hand, the value of thecarrier amplitude varies depending on the amplitude the modulating signal. The envelope of themodulated signal is the same shape as the modulating signal.Hence the Amplitude Modulation Wave is generated using Matlab Software. REFERENCES:  

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el ect r osome. com/ amgener at i onmat l ab

http://www.engineeringradio.us/blog/2011/03/methods-for-generating-amplitudemodulation/ https://electronicspost.com/explain-the-generation-of-am-waves-using-square-lawmodulator-and-switching-modulator/...