This thesis reveals the pros and cons of five demodulation methods for. Ee4512 analog and digital communications chapter 6 the analytical signal for double sideband, large carrier amplitude modulation dsblc am is. 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. All books are in clear copy here, and all files are secure so dont worry about it. As we mentioned before, well use dsbc modulation because of its ease in demodulation.
Modulation and demodulation this chapter describes the essential principles behind modulation and demodulation, which. If not, what is the default depth of modulation for am here. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Modulation damplitude demodulation damplitude pdf book. Am is a method of transmitting signals, such as sound or digital information, in which the amplitude. To study and perform pulse amplitude modulation and demodulation. To study and perform pulse width modulation and demodulation. The process of amplitude modulation consists of the amplitude of the carrier wave being varied in sympathy with a modulating signal. The original amplitude modulation is a family of modulation schemes, in which the amplitude of a. Amplitude modulation is defined as the process in which the amplitude of the carrier wave ct is varied about a mean value, linearly with the baseband signal.
This type of demodulation is therefore called coherent demodulation or detection. In this experiment, a carrier signal and an audio modulating signal are applied to the modulator ic mc 1496 and the produced modulated waveform is observed. I ntroduction an amplitude modulated signal is composed of both low frequency and high frequency components. The most rudimentary form of ask is given the special name onoff keying ook modulation. Communications i amplitude modulations and demodulations dr. 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. Communications i amplitude modulations and demodulations.
Transistors may also be mosfets with appropriate biasing. Amplitude modulation early radio ee 442 spring semester. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. Both processes aim to achieve transfer information with the minimum distortion, minimum loss and. The diagonal clipping in amplitude demodulation using envelope detector can be avoided if rc timeconstant of the envelope detector. The spectral efficiency of the transmitted ask waveform is also a consideration and the m. The purpose of this lab is for you to gain familiarity with the concepts of amplitude modulation and demodulation.
For creating the fpaa circuits, amplitude modulation and synchronous demodulation methods known from designing analogue rf transmission systems have. Understanding the principle of amplitude modulation am. Hi, im a beginner in matlab and im just wondering whether the modulation constant. At the receiving station, the message signal is extracted from the modulated carrier by demodulation. To learn what is happening inside the tims modules by use of mc1496 to. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. The circuits carrier generator, modulator and demodulator are provided with the. In commercial tv transmission in india, picture and speech signals are. In practice, the demodulation of suppressed carrier amplitude modulated signals requires fairly. This video uses properties of the fourier transform to explain modulation and demodulation inside a simple am radio system. In this case, you will use the modulator and demodulator blocks provided by simulink.
Laboratory manual principles of communication system lab ee226f ivth semester prepared by. Amplitude modulation has the obvious advantage of being simple and relatively bandwidth efficient. The focus of this lab is to familiarize the student with the modulation and demodulation of an am signal. The circuit in which restoration is achieved is called the detector or demodulator both of these terms are used in neets. Am modulator and demodulator by the use of mc1496 goal. Amplitude modulation refers to any method of modulating an. Amplitude and frequencyphase modulation i always had di culties in understanding frequency modulation fm and its frequency spectrum.
The idea is simple, though the notion that it can be used to modulate signals. A modem is an equipment that performs both modulation and demodulation. Even for the pure tone modulation, the fm spectrum consists of an in nite number of sidebands. In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors. Explain generation and demodulation of pam, ppm and pwm with waveforms. An am radio signal can be demodulated by rectifying it to remove one side of the carrier, and then. Demodulation of dsbsc the modulator circuits can be used for demodulation, but replacing the bpf by a lpf of bandwidth b hz. Matlab code for amplitude modulation am file exchange. Understanding the waveform and frequency spectrum of am signal and calculating the percent of modulation. Bandpass modulation and demodulation techniques communication systems, dept. The message signal is, for example, a function of the sound to be reproduced by a. The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier. Demodulation is extracting the original informationbearing signal from a carrier wave.
Source called v1 generates the message to be transmitted. If the amplitude of the analog carrier varies with the digital bit stream, the modulation is termed amplitudeshiftkeying ask. Amplitude modulated am signal and four demodulation methods for fre quency. Amplitude modulation am, demodulation and their circuit. In amplitude modulation, the amplitude or strength of the. Read online modulation d amplitude demodulation d amplitude book pdf free download link book now. Frequency modulation consists of encoding information onto a carrier signal by varying the frequency of the carrier. These are then amplitude modulated with the two data streams known as the i. Amplitude modulation am, still widely used in commercial radio today, is one of the simplest ways that a message signal can modulate a sinusoidal carrier wave. Here is the circuit used for modulation and its simulation. Demodulation of dsbsc signal by means of a product detector dsbsc modulator coherent dsbsc demodulator recovered carrier remarks. The frequency modulator and demodulator structures are as explained below. The code for amplitude modulation am with control of modulation index ma has been developed using matlab according to conventional theory. Althoughthereareanumberofwaysinwhicharadio signal may be modulated, one of the easiest is to change its amplitudeinlinewithvariationsofthesound.
Amplitude modulation and demodulation of harmonic signal. 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. In this case, since the source is a multimedia file rather than a pure sine wave, we need the dsp process, which is the resampling and filtering. The second is to investigate classical analog amplitude modulation and the envelope detector. To utilize the coherent demodulator, the receiver must be. 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. As illustrated in figure 5, the amplifier is biased class c and the output rf signal amplitude is modulated by causing the collector supply voltage to vary with the modulation voltage. Pdf realization of lowfrequency amplitude modulator and. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. The amplitude modulation and demodulation technique involved in this project comprises of three stages. Demodulators, or detectors, are circuits that accept modulated signals and recover the original modulating information. The demodulation is performed by an envelope detector.
The amplitude of the high frequency carrier of the signal is. Introduction information capacity, bits, bit rate, baud, and mary encoding amplitude shift keying frequencyshift keying. 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. This principle is at the heart of amplitude modulation. The receiver must generate a carrier frequency in phase and frequency synchronization with the incoming carrier.
Download modulation d amplitude demodulation d amplitude book pdf free download link or read online here in pdf. What three functions does the transistor in a regenerative detector serve. Overmodulated am signals and its requirement for coherent detection are also considered. Talal skaik 2016 islamic university of gaza electrical engineering department 1 dsbsc amplitude modulation is easy to understand in both time and frequency domains, but it is not simple in practical. In this code, it is considered the default value of ma equal to 1 for hundred percent modulation. Restoring or recovering the message signal from the received modulated waveform that is generally corrupted by noise.
Amplitude modulation was the first modulation type to be considered in analog communication systems. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. Digital modulation modulation frequency modulation. It is still in use today in a variety of systems, including, of course, am broadcast radio. In the second model, you will observe the frequency variations with respect to the input signals waveform. Each channel sharing scheme a set of basis vectors. Once a signal has been modulated, information is retrieved through a demodulation process. Electronic communications is the transmission, reception, and processing of information with the use of electronic circuits information is defined as the knowledge or intelligence that is communicated between two or more. Both phase and frequency of carrier are known at the demodulator amplitude of. The term demodulator is used because the demodulation process is considered to be the opposite of modulation. Matlab tutorial amplitude modulation how to generate amplitude modulation am using matlab. In the first model, you are provided a fm structure that is very similar to the theoretical background of this experiment. Based on your location, we recommend that you select. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation.
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. The concluding part will be spent looking at the more popular form of high level modulation known as collector modulation or heising, named after its inventor. What is amplitude modulation in order that a radio signal can carry audio or other information for broadcasting or for two way radio communication,itmustbemodulatedorchangedinsome way. Understand the principle of amplitude modulation know how to modulate a signal to a certain frequency know how to demodulate a signal back to the baseband can write the equation and draw block diagram for both modulation and demodulation can plot the signal spectrum after modulation and demodulation. Analog modulation and demodulation amplitude modulation pages 306309. As in the case of dsb, product detector recovers the message signal without any distortion g. When expressed as a percentage it is the same as the depth of modulation. Modulation and demodulation techniques for fpgas ray andraka p.
Choose a web site to get translated content where available and see local events and offers. Explain generation and demodulation of pam, ppm and pwm. To study and perform pulse position modulation and demodulation. Amplitude modulation consists encoding information onto a carrier signal by varying the amplitude of the carrier.
26 1083 260 484 1117 1474 35 1008 947 1500 1479 595 95 797 759 1529 505 1539 215 320 86 357 103 765 929 1067 299 753 1091 1125 453 143