A foundation in digital communication, written by amos lapidoth, is a systematic and insightful book, with over 300 exercises, is ideal for graduate courses in digital communication, and for anyone asking why and not just how. In amplitude modulation, i have covered standard amplitude modulation, dsbsc double sideband suppressed carrier, ssbsc single sideband suppressed carrier, vsb vestigial sideband. The transmission bandwidth required by dsb sc is b t2b. This principle is at the heart of amplitude modulation. The modulating signal contains the intended message or information sometimes consisting of audio data, as in am radio. Amplitude modulation am is a method of impressing data onto an alternatingcurrent ac carrier waveform. Ec8395 important questions communication engineering regulation 2017 anna university free download. A disadvantage of all amplitude modulation techniques, not only standard am. 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.
For example, the very lowspeed bell system 103 modem standard for 300. What is amplitude modulation, am electronics notes. After continuous wave modulation, the next division is pulse modulation. This set of data communication and networking multiple choice questions and answers mcqs focuses on digital to analog to encoding modulation techniques amplitudeshift keying ask frequencyshift keying fsk phaseshift keying psk quadrature amplitude modulationqam. Amplitude modulation am is a modulation technique where the. Accordingly it is worth looking at some of the disadvantages of amplitude modulation. No information is lost, but the energy is redistributed in the frequency domain. This intuitive yet rigorous introduction derives the core results of digital communication from first principles.
That could be the amplitude, phase, or frequency, which result in amplitude modulation am, phase modulation pm, or frequency modulation fm. Sep 15, 20 lecture 8 amplitude modulation nptelhrd. The notes below are primarily still images of the slides and boards seen in the lecture videos. Amplitude modulation among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. Amplitude modulation can be carried out by linearly combining the carrier and intelligence signals then applying the result to a nonlinear component or circuit. The message signal is, for example, a function of the sound to be reproduced by a. Rc audio generator, oscilloscope, and spectrum analyzer demonstrations with speech and radio. Amplitude modulation article about amplitude modulation. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Lecture notes on analogue communication techniques 1. Many fm radio stations transmit music programs in stereo by using the outputs of two.
Amplitude modulation is a very basic form of modulation, and although its simplicity is one of its major advantages, other more sophisticated systems provide a number of advantages. The authors have created a massive open online course mooc that covers some of the same material as the first half of this book. Amplitude modulation, spectrum of am signal, the balanced modulator, the square law demodulator, dsbsc, ssbsc and vsb, their methods of generation and demodulation, carrier acquisition, phaselocked loop pll, frequency division multiplexing. The am generator, or exciter, as such a low power source of modulated signal is often called, is now set up. Introduction to amplitude modulation virginia tech. Click the below links to download cds lab manual 1. Digital to analog encoding modulation techniques ask. The second is to investigate classical analog amplitude modulation and the envelope detector. In this method of modulation the amplitude of the carrier wave is maintained constant. Pulse position modulation ppm is an analog modulation scheme in which, the amplitude and the width of the pulses are kept constant, while the position of each pulse, with reference to the position of a reference pulse varies according to the instantaneous sampled value of the message signal. Security by using coding techniques to avoid jamming. Amplitude modulationwhich of course is the origin of the term am radiovaries the amplitude of the carrier according to the instantaneous value of the baseband signal. Amplitude modulation am is a modulation technique used in electronic communication, most. When the modulator has a dc offset, the carrier frequency will remain present in the output sound, along with sidebands at frequencies determined by the sum and the difference of the.
Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Tcom 370 notes 995 modulation and demodulation modems for. Amplitude modulation early radio ee 442 spring semester. In the case of digital data, the justification of the modulation must be clear. The mathematical relationship for amplitude modulation is simple and intuitive. Capability for phase modulation and frequency modulation is provided internally in the. In am radio broadcasts, is the audio signal being transmitted usually bandlimited to less than 10 khz, and is the channel center frequency that one dials up on a radio receiver.
The highest frequency of the modulating data is normally less than 10 percent of the carrier frequency. Free pdf download a foundation in digital communication. Types of modulation 6 flynnkatz 7810 analog modulation amplitude modulation, am frequency modulation, fm double and single sideband, dsb and ssb digital modulation phase shift keying. The measurement and definition of amplitude modulations. Digital modulation and demodulation fsk,psk,bpsk,qpsk techniques. Most radio systems in the 20th century used frequency modulation fm or amplitude modulation am for radio broadcast a modulator is a device that performs modulation. In pulse amplitude modulation pam technique, the amplitude of the pulse carrier varies, which is proportional. Both amplitude and phase of ft carry information of ft. However, in order to modulate the amplitude of the output signal, a low power dac or digital potentiometer is required to set the fullscale current. 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. Pulse modulated signals, such as pam, pwm, ppm, pcm and dm are actually baseband digital signal coding and not the result of frequency conversion.
You can publish your book online for free in a few minutes. The modulated signal can be written as the sum of the unmodulated carrier wave. Amplitude modulation am 9 t15 use speech or music from trunks as the message, and show that this also generates a trapezoid, and that setting the message amplitude so that the depth of modulation reaches unity on peaks a triangle is especially easy. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. What is modulation 2 modulation in the modulation process, some characteristic of a highfrequency carrier signal bandpass, is changed according to the instantaneous amplitude of the information baseband signal. Amplitude modulation, spectrum of am signal, the balanced modulator, the square law demodulator, dsbsc, ssbsc and vsb, their methods of generation and demodulation, carrier. If you are new to matlab, please go through our tutorials.
Angle modulation is the process in which the frequency or the phase of the carrier varies according to the message signal. In this type of modulation scheme for twolevel pulses we always put out a pulse pt that is amplitude modulating a carrier frequency, whether the data digit is a 1 or a 0, but we distinguish between the two digits by using two slightly different carrier frequencies f1 and f 2. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. Pulse amplitude modulation using matlab with waveforms. Amplitude modulation a continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. The instantaneous amplitude overall signal power varies depending on the instantaneous amplitude of the modulating data. Pulse modulated signals, such as pam, pwm, ppm, pcm and dm are baseband digital signal coding and not the result of frequency conversion.
The intensity of the amplitude modulation can be controlled by increasing or reducing the amplitude of the timevarying modulator relative to its dc offset. Quadrature amplitude modulation eprints soton university of. There are many ways in which amplitude modulation can be generated and a variety of circuits that can be used. There are no amplitude scales shown, but you should be able to deduce the depth of modulation 1 by inspection. A sine wave carrier can be modified by the intelligence signal through amplitude modulation, frequency modulation, or phase modulation. Modulation has defined as the process of combining an input signal m t and a frequency carrier fc to produce an s t signal whose bandwidth is usually centred around fc. Amplitude modulation article about amplitude modulation by.
Historically one on the earliest forms of coding a signal prior to transmission. The amplitude or the strength of a high frequency carrier wave is changed in accordance with the amplitude of message signal. Because of amplitude modulation wavelength, am signals can propagate longer distances. Tags amity university notes, amity notes, am notes, amplitude modulation notes, notes for amity university, download, 4th sem notes, view, pdf file, ppt. Ec8395 important questions communication engineering. 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. For amplitude modulation, we use simple and low cost circuit. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Amplitude modulation am is a one of the conventional modulation technique to transmit signals using a carrier wave. Ask, fsk, psk, and qam are all forms of digital modulation. 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. A voltage output dac can be used to drive the fs adjust pin of the ad9834 through a series resistor. Oct 14, 20 amplitude modulation am is a one of the conventional modulation technique to transmit signals using a carrier wave.
Adaptation of the information signal to the transmission channel. This ocw supplemental resource provides material from outside the official mit curriculum. Winter 2003 uw, ece 318 lecture notes 1 amplitude modulation part 1 instructor. Transmitters that transmit amplitude modulated signals require an am modulator circuit to produce the required signal.
Amplitude shift modulation ask, frequency shift modulation fsk and phase shift modulation psk. Communication engineering important questions ec8395 pdf free download. Amplitude modulation explained amplitude modulation waveform and equation hd. These form some of the main uses of amplitude modulation. Amplitude modulation in analog communication amplitude modulation in analog communication courses with reference manuals and examples pdf. In early am transmitters the amplitude modulator circuit was a key element of the transmitter.
Lecture notes signals and systems mit opencourseware. The depth of modulation, defined below, can be adjusted with the adder gain control g. In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. Analog communication pulse modulation tutorialspoint. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation a continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Open gnu radio companion by clicking on the grc icon at the top of the screen or through the menu. Electromagnetic theory and transmission lines emtl notes and textbook download click the below links to download ec05214anotes1. Amplitude modulation in analog communication tutorial 19. A typical f c for lowrate telephone line modems is 1800 hz approximate center of 300 3400 band, and for 1200 baud signaling 1200 pulses per. Process by which a property or a parameter of a signal is varied in proportion to a second signal. Qam is the most efficient of these options and is the mechanism used in all modern modems. The pulse may take any real voltage value that is proportional to the value of the original waveform.
Mar, 2020 in amplitude modulation, i have covered standard amplitude modulation, dsbsc double sideband suppressed carrier, ssbsc single sideband suppressed carrier, vsb vestigial sideband. Amplitude modulation fundamentals i n the modulation process, the baseband voice, video, or digital signal modifies another, higherfrequency signal called the carrier, which is usually a sine wave. Amplitude modulation can be accomplished by multiplying the carrier sine wave by a gain or attenuation factor that varies in accordance with the intelligence signal 2. Sinusoidal amplitude modulation am mathematics of the dft. Hapter modulation and demodulation mit opencourseware. Besides, there is a fourth mechanism and better that combines changes in phase and amplitude and is called quadrature amplitude modulation qam. We can choose the signal constellation such that the amplitude is the same for all signal alternatives, by placing the signal vectors on a circle in the signal space. To solve this problem, one solution is to emit a radio wave fixed frequency, the socalled wave carrier, which is modified in amplitude function of the sound wave, which is the wave source.
This tutorial will use a gnu radio flowgraph to demonstrate simulations of two different amplitude modulations. Sample ec8395 important questions communication engineering. Effectively it is formed by having two carriers 90 out of phase. Qam structure consider the yt in the transimitter yt x1tcos. Demonstration with professor sandy hill from the university of massachusetts at amherst. Amplitude modulation in analog communication tutorial 19 may.
In this chapter, let us discuss the following analog pulse modulation techniques. Amplitude modulation am8 in amplitude modulation, the message signal mt is impressed on the amplitude of the carrier signal ct accos2 fct this results in a sinusoidal signal whose amplitude is a function of the message signal mt there are several different ways of amplitude modulating the carrier signal by mt each results in. Why modulation is used suitable for signal transmission distanceetc. Introduction ang man shun december 20, 2012 to send multiple signals at one time, one way is to use qam.
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