Modulation and demodulation in communication engineering. Pulse amplitude modulation pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. Analog modulation and demodulation amplitude modulation pages 306309. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. To study and perform frequency modulation and demodulation. To study frequency modulation and determine its modulation factor 4. Amplitude modulation or am is a method to transmit signals via electromagnetic transmission. Students will explore the mathematical theory behind amplitude modulation and use the analog discovery 2 to visualize the effects of amplitude modulation in the time and frequency domains. Ee4512 analog and digital communications chapter 6 chapter 6 analog modulation and demodulation amplitude modulation pages 306309. Discretetime qam demodulator timereversal of the pulse shaping filter note. A basic amplitudemodulated doublesideband full carrier signal is obtained by mixing a modulating signal y m t at a modulation index m and frequency. Amplitude modulation a continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. But the term demodulation tends to be used more widely when referring to the process of extracting the modulation from the signal.
Amplitude modulation definition, types, solved examples. Frequency modulation and phase modulation is a system in which the amplitude of the modulated carrier is kept constant, while its frequency and rate of change are varied by the modulating signal. It is a kind of modulation where the amplitude of the carrier signal is changed in proportion to the message signal while the phase and frequency are kept constant. That could be the amplitude, phase, or frequency, which result in amplitude modulation am, phase modulation pm, or frequency modulation fm. A modem is an equipment that performs both modulation and demodulation. Vsb signals are generated using standard am or dsbsc modulation, then passing modulated signal through a sideband shaping. Telo, chapter 9, modulation, demodulation, signal sampling. Farshad lahouti january 20, 2003 winter 2003 uw, ece 318 lecture notes 2 information source signal modulator propagation channel signal demodulator information destination analog communication system analog signals may be transmitted directly via carrier modulat ion over.
Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. Each channel sharing scheme a set of basis vectors. To understand the theoretical foundations of analog communications as well as of doublesideband amplitude modulation and demodulation dsbam to design the simulink model of the dsbam to analyze each signal in time and frequency domains using time scope and spectrum analyzer. Amplitude modulation am, demodulation and their circuit implementations. Typical modulation system the reverse process is called demodulation. The process and the signal were called amplitude modulation, or am for short. Seeing a little of the theory and mathematics behind amplitude modulation gives a better understanding of how it works. Modulation can be defined as the process of impressing information from a modulating signal onto another signal called the carrier. This chapter describes the essential principles behind. Hi, im a beginner in matlab and im just wondering whether the modulation constant. However, as you can imagine the noise from the nature i. Modulation and demodulation pdf on the various aspects of modulation and demodulation.
Vsb modulation with envelope detection is used to modulate image in analog tv signals. The circuit in which restoration is achieved is called the detector or demodulator both of these terms are used in neets. Radio frequency spectrum sound need for modulation radio broadcasting modulation methods of modulation amplitude modulation percent modulation upper and lower sidebands mathematical analysis of a modulated carrier wave power relation in an am. Doublesideband suppressedcarrier transmission wikipedia.
Amplitude modulation contents slide 1 amplitude modulation slide 2 the envelope and no overmodulation slide 3 example for single tone modulation slide 4 measuring the modulation index slide 5 transmitted vs. In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. Learn about the most straightforward way of encoding information in a carrier waveform. For amplitude modulation, the process of demodulation or detection can be accomplished very simply using a diode, or it may be achieved in other ways that provide more effective demodulation of the waveform. On amplitude and frequency demodulation using energy operators article pdf available in ieee transactions on signal processing 414. Read online modulation d amplitude demodulation d amplitude book pdf free download link book now. Ee4512 analog and digital communications chapter 6 the analytical signal for double sideband, large carrier amplitude modulation dsblc am is. It is not an easy task to transmit a message signal directly as with the propagation of the signal, several factors degrade its quality. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Theory shows that in order to transmit a wave effectively, the length of the. Radio modulation modes telecommunication theory television terminology. In chapters 1 and 2 you studied how to apply intelligence modulation to an rf carrier wave. Pdf amplitude modulation and demodulation dikshya rath.
The radio wave was called a carrier, since it was seen to carry the speech information with it. In the context of radio communication, near the end of the 2oth century, few modulated signals contain a significant component at carrier frequency. This shout can be heard only up to a certain distance. Demodulation uses either standard am or dsbsc demodulation, depending on whether a carrier tone is transmitted. To study and perform amplitude modulation and demodulation. Radio waves can carry audio, video, and digital information over great distances by using changes in a carrier waves amplitude, frequency, or phase to represent the information being transmitted. Modulationsverfahren zur sprachubertragung pdf 186 kb. Recall that our goal is to transmit data over a commu nication link, which we achieve by mapping the.
Restoring or recovering the message signal from the received. This type of modulation comes under digital modulation schemes. What is digital modulation and state various techniques. Amplitude modulation and demodulation objective amplitude modulation am is one of the simplest methods for modulating a sinusoidal carrier wave. But the width of each pulse is made properly proportional to the amplitude of the signal at that instant. Why frequency modulation is better than amplitude modulation. When building a model, we simply pass it through the pulseshaping filter again xkt s. Theory pulse width modulation is also referred as pulse duration modulation or less often pulse length modulation. This is the modulation where the phase of the carrier signal is altered according to the low frequency of the message signal is called phase modulation. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. Modulation and demo dulation 66c h a p t e r learning objectives what is a carrier wave. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i.
Explain generation and demodulation of pam, ppm and pwm with waveforms. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. Hapter modulation and demodulation mit opencourseware. Some phase modulation and quadrature amplitude modulation formats have a higher spectral efficiency for data transmission than frequency shift keying, a form of frequency modulation. Finally, the significance of an adequate demodulator bandwidth is highlighted during highspeed.
Explain generation and demodulation of pam, ppm and pwm. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. In electronics and telecommunications, modulation is the process of varying one or more. In amplitude modulation am, we utilize the amplitude of the audio signal to modulate the amplitude of carrier signal, which means that the amplitude of carrier signal will be varied with the amplitude of the audio signal. Aly elosery october 25, 2010 this lab is divided into two parts. This modification is performed according to a specific scheme that is. In radio communications, singlesideband modulation ssb or singlesideband suppressedcarrier modulation ssbsc is a type of modulation used to transmit information, such as an audio signal, by radio waves. Both phase and frequency of carrier are known at the demodulator amplitude of carrier is not important since it in.
We can define amplitude modulation by saying that a modulating signal, should produce an am wave of the form well use s instead of v or e to indicate that were talking about a modulated quantity and that it can be either a field or a voltage. In theory the total integrated noise approaches zero as the filter. What we do in am, very roughly,is to throw away the frequency content of. There are many types of modulation so there are many. In this lab, students investigate two methods to recover an amplitude modulation am signal in order to develop an understanding of the demodulation process in the time and frequency domain. To study and perform pulse amplitude modulation and demodulation. In part i you will learn how to design an amplitude modulator am and in part ii you will be able to demodulate an am signal. In this chapter we will discuss ways of demodulating am, cw, fm, phase, and pulse modulation. To study sampling and reconstruction of pulse amplitude modulation system 6. The goal of this experiment is to become familiar with fm modulation and demodulation. This chapter describes the essential principles behind modulation and demodulation, which we introduced briefly in chapter. There are many types of modulation so there are many types of demodulators.
The demodulator is the circuit, or for a software defined radio, the software that is used to recover the information content from the overall incoming modulated signal. Frequency modulation, fm detection, demodulation, discrimination in order to use the modulation on an fm signal, it is necessary to extract the modulation, i. But the width of each pulse is made properly proportional to the amplitude of. Laboratory manual principles of communication system lab ee226f ivth semester. The term detection is the older term dating back to the early days of radio. Amplitude modulation a1 53 experiment aligning the model the low frequency term at to generate a voltage defined by eqn.
Amplitude modulation can be produced in various ways. A demodulator is an electronic circuit or computer program in a softwaredefined radio that is used to recover the information content from the modulated carrier wave. Seeing a little of the theory and mathematics behind amplitude modulation gives a better understanding of how it. The wave form of am modulation is shown in figure 3.
The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. The term demodulator is used because the demodulation process is considered to be the opposite of modulation. Amplitude demodulation matlab amdemod mathworks india. Overmodulated am signals and its requirement for coherent detection are. The responses are compared against the theoretical. This video is about the demodulation detection of pulse width modulation pwm and pulse position modulation ppm. In practice, the carrier may be highfrequency hf while the modulation is audio. In modulation, one characteristic of a signal generally a sinusoidal wave known as the carrier is changed based on the information signal that we wish to transmit modulating signal. Its still used in radio systems to transmit audio signals although it has lesser in popularity compared to fm due to its lower signal to noise ratio. Assuming that m 0 for the msample delay no delay, plot the coef. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. The process of demodulation for signals using amplitude modulation can be achieved in a number of different techniques, each of which has its own advantage.
In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Pdf on amplitude and frequency demodulation using energy. The process of separating or extracting the modulation from a signal is called demodulation or detection. Demodulation of pwm and ppm block diagram and waveform. To study amplitude demodulation by linear diode detector 3. This gives us something to modulate and carry the information pattern from place to place. This principle is at the heart of amplitude modulation. In amplitude modulation theory, the amplitude of a carrier signal is varied by the modulating voltage, whose frequency is invariably lower than that of the carrier. The fmmodulated signal has its instantaneous frequency that varies linearly with the amplitude of the message signal. We will use the basic demodulation approach with full rectification and low pass filter followed by a dc removal. What is analog modulation and state various techniques. Theory of amplitude modulation let us now move further in order to have a detailed discussion about how a signal gets amplitude modulated.
In the diagram, the modulation frequency, km, is 500. Yet, am continues to be used today in many communication applications. The theory developed here does not take account of interference such as clutter or manmade static, but assumes only random. Here well use the example of a square law fet as illustrated in figure 9. Download modulation d amplitude demodulation d amplitude book pdf free download link or read online here in pdf. Terms like diode detector, synchronous detector and product detector are widely used. Theory of frequency modulation and phase modulation. If not, what is the default depth of modulation for am here. To study and perform pulse position 6 to study and perform pulse code modulation and demodulation.
Demodulation is extracting the original informationbearing signal from a carrier wave. The theory and equations show that furthest extent of the sidebands from the carrier corresponds to the highest frequency of the modulating tone for the amplitude modulated signal. Modulation is the process of influencing data information on the carrier, while demodulation is the recovery of original information at the distant end from the carrier. Amplitude modulationdemodulation in matlab file exchange. Amplitude modulation am, demodulation and their circuit. Each part may be of any convenient amplitude at the input to an adder.
Amplitude modulation theory frequency spectrum power. If the received carrier phase is assumed to be constant, each of the seven reference values will have to be shifted only once at the beginning of the simulation. In this video, i have explained amplitude modulation by following outlines. The demodulation is performed by an envelope detector. A modem from modulatordemodulator can perform both operations. Message power in st slide 6 powers in single tone case cont. It is a modulation system in which the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the signal at the instant of sampling. This lab introduces students to communications theory with amplitude modulation and demodulation.
The resulting signal is called the modulated signal in general, it is a bandpass signal. Apr 12, 2015 modulation and demodulation in communication engineering 1. By the amplitude shift keying theory, we can understand the process of ask technique. The ad630 is a high precision balanced modulatordemodulator. In order for the lowpass to detect the information envelope, the frequency of the carrier must be as high as possible. Keying is indicating the transmission of digital signal over the channel. For the sake of simplicity, ka 1 and ar ac have been chosen lowpass. Doublesideband suppressedcarrier transmission dsbsc is transmission in which frequencies produced by amplitude modulation am are symmetrically spaced above and below the carrier frequency and the carrier level is reduced to the lowest. Inspired by imagerejection mixers 33 and modulateddemodulated control. We have seen that rf modulation is simply the intentional modification of the amplitude, frequency, or phase of a sinusoidal carrier signal. Here, we consider a modulator approach that will be considered again in some other carrier modulation schemes to be introduced in later lectures.
Amplitude modulation qam 4 ee4900ee6720 digital communications suketu naik quadratureamplitude modulation qam applications qam rhymes with guam and vietnam is commonly. In this system we have a fixed amplitude and starting time of each pulse. In this video you will learn the block diagram of pwm and ppm. Oct 30, 2017 amplitude modulation and demodulation. In chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave. Is there a way i can vary it, say, to 100% modulation depth. It requires that the amplitude of the dc a part of a t is equal to the amplitude of the ac part a. Using the absolute value, filter, and acdc estimator vi functions, implement the demodulation of am signal to on the same modulation block diagram as shown below. Pulse amplitude modulation is the basic form of pulse modulation in which the signal is sampled at regular and each sample is made proportional to the amplitude of the modulating signal at the sampling instant. Carrier modulation allows the transmission of modulating frequencies. The purpose of this lab is for you to gain familiarity with the concepts of amplitude. All books are in clear copy here, and all files are secure so dont worry about it.