Amplitude modulation and demodulation university of st andrews. This book features indepth discussions on amplitude modulation afm, providing an overview of the theory, instrumental considerations and applications of the technique in both academia and industry. This chapter focuses on amplitude modulation systems. You can publish your book online for free in a few minutes. Amplitude modulator and demodulator circuits unimap portal. Amplitude modulation a1 53 experiment aligning the model the low frequency term at to generate a voltage defined by eqn. Frenzeljr, in handbook of serial communications interfaces, 2016. Along with circuit components, introductions, an appendix section which. Theory, time domain, frequency domain radio frequency modulation in our free electronics textbook. It was developed in the first few decades of the twentieth century. The carrier frequency, fc, should be larger than the highest spectral component.
Use fg1 as the message signal and fg2 as the carrier signal. The message signal is, for example, a function of the sound to be. 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. Amplitude modulation an overview sciencedirect topics. The resulting plate current flows in pulses, the amplitude of each pulse being proportional to the instantaneous bias and therefore to the instantaneous modulating voltage. Dec 21, 2017 amplitude modulation is one of the earliest radio modulation techniques. Notice that the sine wave will move up and down as the dc is varied, its mean value equalling the dc value. This book is written in a way that a student with basic understanding on electronic circuit theory can learn the theory and experiment. The spectral efficiency of the transmitted ask waveform is also a consideration and the m. Peter wilson, in the circuit designers companion fourth edition, 2017. Each part may be of any convenient amplitude at the input to an adder.
Double sideband suppressed carrier modulation dsbsc. Frequency modulation keeps constant the amplitude of the highfrequency oscillation that is used as a signal and to vary the instantaneous frequency for presenting the information. It is possible to look at the theory of the generation of an amplitude modulated signal in four steps. In amplitude modulation, it is the voltage level of the signal to be transmitted. Another way to think is to realize that we are really plotting the amplitude.
For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Amplitude modulation which 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 produces an output signal the bandwidth of. 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. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. Quadrature amplitude modulation qam national instruments. The complex constant, which encapsulates amplitude and phase dependence, is known as phasor, complex amplitude, and in older texts sinor or even complexor. Amplitude modulation atomic force microscopy wiley. The binary signal when ask modulated, gives a zero value for low input while it gives the carrier output for high input.
Chapter 7 amplitude modulation techniques generation and detection chapter outline 7. 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. Signal analysis, and most of communication theory, is a mathematical science. Well there are many good books for studying analog modulation as well as for digital modulation.
The modulated signal can be written as the sum of the. The highest frequency of the modulating data is normally less than 10 percent of the carrier frequency. Communication systemsamplitude modulation wikibooks, open. Am an amplitude modulated signal that contains the carrier signal and. Dec 05, 2014 amplitude modulation the amplitude of the carrier is changed in accordance with the instantaneous value of modulating signal carrier. In theory and design of electrical and electronic circuits you can find primarily the generalities of circuits. The application of these pulses to the tuned tank circuit will give amplitude modulation. We give the theory and the experimental results of the modified switching modulator. The idea is simple, though the notion that it can be used to modulate signals for transmission was hardly obvious before its discovery.
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. Amplitude modulation electronics and communication. 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. 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. As we mentioned before, well use dsbc modulation because of its ease in demodulation. Remember, for analysis purposes keep the modulation index and frequency the same as part 2, step 3. Amplitude modulation is mostly used in the form of electronic communication. Electronic circuits pdf is a great book for electronic circuits enthusiasts who are keen to learn electronic and electrical circuit. The simplest method for representing this kind of modulation is fresnels vectorial representation with a consideration of the phase. Source called v1 generates the message to be transmitted. A demodulator is an electronic circuit that is mainly used to recover the information content from the modulated carrier wave. Am modulators base, collector, grid and plate modulators.
In this video, i have explained amplitude modulation by following outlines. Am is a relatively simple way to add audio information to a carrier wave so that sounds can be transmitted. Here is the circuit used for modulation and its simulation. Amplitude modulation is a simple method to transmit a signal for example sound, from one end to other.
One of the easiest ways to implement qam with hardware is to generate and mix two sine waves that are 90 degrees out of phase with one another. Analog communication pulse modulation tutorialspoint. 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. That could be the amplitude, phase, or frequency, which result in amplitude modulation am, phase modulation pm, or frequency modulation fm. Therefore, when we receive the amplitude modulation signal, we need to restore the audio signal. In a hybrid modulation with the following constellation pattern, the outlying signal sig2, has higher energy i. Amplitude shift keying ask is a type of amplitude modulation which represents the binary data in the form of variations in the amplitude of a signal. Timedomain description, frequencydomain description, generation of am wave.
Amplitude modulation definition and its applications. This book is written in a way that a student with basic understanding on electronic circuit theory can learn the theory and experiment the basics of analog communication techniques. This conforms to the expectation as the maximum and minimum peak of the modulated signal waveform varies proportional to the amplitude of the modulating signal. Amplitude modulation am broadcastband transmitter power levels tend to be around 100500 kw, but the transmitters are usually located away from centers of population. A cw wave, an audio wave, and the resulting amplitude modulated. Frequency multipliers, detector circuits, phaselocked loops and frequency.
A musical tone of hz is to be used for modulation. Amplitude modulation circuit implementation for use in. Double sideband suppressed carrier modulation in amplitude modulation the amplitude of a highfrequency carrier is varied indirect proportion to the lowfrequency baseband message signal. 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.
Mar 05, 2019 quadrature amplitude modulation qam requires changing the phase and amplitude of a carrier sine wave. 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. To generate amplitude modulation am waveform and to measure modulation index of am wave using waveform method. As such, it includes examples from material science, soft condensed matter, molecular biology, and biophysics, among others. It is strongly suggested that you examine your text book for other methods. It requires that the amplitude of the dc a part of a t is equal to the amplitude of the ac part a. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. Index terms amplitude modulation, analog circuit, analog modulator. Quadrature amplitude modulation qam requires changing the phase and amplitude of a carrier sine wave. The modulating signal contains the intended message or information sometimes consisting of audio data, as in am radio.
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. As in figure 34, the application of these pulses to the tuned tank circuit will yield generation of amplitude modulation. By the end of this module, you will know the most popular versions of amplitude modulation, some popular am modulation circuits, and some popular am. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Understanding reflections and standing waves in rf circuit design. Introduction to communication theory sciencedirect. 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. Amplitude modulation, am, is one of the most straightforward ways of modulating a radio signal or carrier. Apr 25, 2015 well there are many good books for studying analog modulation as well as for digital modulation. Amplitude modulation early radio ee 442 spring semester.
The instantaneous amplitude overall signal power varies depending on the instantaneous amplitude of the modulating data. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. Amplitude modulation am the process of combining the message. Communication systemsamplitude modulation wikibooks. Practical guide to radiofrequency analysis and design. Use the spectrum analyzer to compare this modulator to the one in part 2. Amplitude modulation am is a modulation technique where the. The original method of electronically encoding sound information on radio waves is called amplitude modulation, or am. Jun 17, 2018 in this video, i have explained amplitude modulation by following outlines. About this book filling a gap in the literature, this book features indepth discussions on amplitude modulation afm, providing an overview of the theory, instrumental considerations and applications of the technique in both academia and industry. It travels in the air like waves, read more about amplitude modulation and its applications at. Demodulation is defined as extracting the original informationcarrying signal from a modulated carrier wave.
Amplitude modulation am is a method of impressing data onto an alternatingcurrent ac carrier waveform. Amplitude modulation am, demodulation and their circuit. Explain briefly in your report how amplitude modulation is accomplished by this circuit. Then as the audio signal amplitude is changed to 150 mvpp, the percentage modulation dropped to around 30%. Field strength levels in the 110 vm range may be experienced occasionally, but at medium frequencies coupling to circuit. The receivers used to listen to amdsbc are perhaps the simplest receivers of any radio modulation technique. Chapter 7 amplitude modulation techniquesgeneration and. 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. It requires that the amplitude of the dc a part of at is equal to the amplitude of the ac part a. Qam is composed of two independent pulse amplitude modulation pam baseband modulations placed on the quadrature rails. Connect channel 1 probe of the oscilloscope to the output of the modulator at pin 7. The resulting plate flows in pulses, the amplitude of each pulse being proportional to the instantaneous bias and therefore to the instantaneous modulating voltage. The mathematical relationship for amplitude modulation is simple and intuitive.
Using a modulation circuit, the amplitude of the carrier wave is made to vary at the audio signal rate. The carrier is usually a sinusoidal waveform, that is, ctac cos. Explain the relationship of the basic equation for an am signal to production of amplitude modulation, mixing and frequency conversion by a diode or other nonlinear frequency component or circuit. So a longer vector has a larger amplitude and hence higher energy. This book has been written in response to the following core question. Analog communication laboratory manual santhosh thottingal. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. Describe the operation of diode modulator circuits and diode detector circuits.
Other methods of demodulating an am signal use synchronous techniques and provide much lower levels of distortion and improved reception where. From experiment 3, we know that the amplitude modulation signal utilizes the amplitude of audio signal to modulate high frequency carrier signal. Generation of amplitude modulation basic requirements. Practical circuitry is more likely to use a modulator, rather than the more idealised multiplier. Amplitude modulation can be carried out by linearly combining the carrier and intelligence signals then applying the result to a nonlinear component or circuit. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. It can be achieved in a number of ways, but the simplest uses a single diode rectifier circuit. Amplitude modulation am assume a radio transmitter is operating on a frequency of khz. Amplitude, frequency and phase modulation can be applied directly by software to the generated signals, which gives great flexibility where complicated and precise waveforms are required. Sinusoidal amplitude modulation am mathematics of the dft. The basic theory and equations behind amplitude modulation are relatively straightforward and can be handled using straightforward trigonometric calculations and manipulation.
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