Basic principles of amplitude modulation figure 44 a squarelaw circuit for producing am. The carrier frequency, fc, should be larger than the highest spectral component. To study sampling and reconstruction of pulse amplitude modulation system 6. Amplitude modulation am in am, the modulating signal the message signal mt is impressed on to the amplitude of the carrier. Amplitude modulation definition, types, solved examples. Pdf amplitude modulation and demodulation dikshya rath.
Modulation is a process by which some characteristics of the carrier signal like its amplitude, frequency or phase are varied in proportion to message signal. Source called v1 generates the message to be transmitted. The distortion may be in amplitude, frequency, or phase, depending on the nature of the demodulator. Its important to understand that the received signal could be from. Vestigial sideband amplitude modulation vsbam is a modulation that improves the spectral e. Analogue modulation amplitude modulation v c t v c cos c t, peak amplitude v c, carrier frequency c radians per second. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation.
Quadrature amplitude modulation, qam tutorial includes. A demodulator is an electronic circuit that is mainly used to recover the information content from the modulated carrier wave. Digital demodulator of the quadrature amplitude modulation. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Modulation and demodulation based interview questions. The message signal is, for example, a function of the sound to be reproduced by a. Amplitude modulation and demodulation of harmonic signal. Analog modulation and demodulation amplitude modulation pages 306309.
Amplitude modulation circuit implementation for use in. Describe fm demodulation circuit operation for the phaseshift and gatedbeam discriminators and the ratiodetector demodulator. 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. Frequency modulation consists of encoding information onto a carrier signal by varying the frequency of the carrier. In fact, all radio channels in the am band use this type of modulation. Quadrature amplitude modulation qam pam signals occupy twice the bandwidth required for the baseband transmit two pam signals using carriers of the same frequency but in. The modulation and demodulation of quadrature amplitude modulation, qam utilises circuits that are able to accommodate both i and q components. This is the same as the am modulation above but without the carrier.
Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. This is the most widely used type of am modulation. There are different types of modulation and so are demodulators. Then, students will use labview to program an am demodulator and use it to explore and visualize the. The signal output from a demodulator may represent sound an. Demodulation is a key process in the reception of any amplitude modulated signals whether used for broadcast or two way radio communication systems. Read online modulation damplitude demodulation damplitude book pdf free download link book now. Demodulation is extracting the original informationbearing signal from a carrier wave. 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. Let us examine the spectrum of the demodulated dsbsc signal. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation.
Failure to accurately recover this intelligence will result in distortion and degradation of the demodulated signal and intelligence will be lost. To study amplitude demodulation by linear diode detector 3. Vectors and modulation cse 466 interfacing 3 spose m and n are orthogonal unit vectors. Download modulation damplitude demodulation damplitude book pdf free download link or read online here in pdf.
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. There are many types of modulation so there are many types of demodulators. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Now i project onto m and onto n to get back the numbers. Assuming that m 0 for the msample delay no delay, plot the coef. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. 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. The circuits carrier generator, modulator and demodulator are provided with the. Ee3 lab 1 amplitude modulation and demodulation broadcast analog television tv signals have a bandwidth of approximately 6mhz and this is achieved with a quadrature modulation. Note that the modulated signal envelope corresponds to the wave form of the dsb am modulating signal. In the diagram, the modulation frequency, km, is 500. There are no amplitude scales shown, but you should be able to deduce the depth of modulation 1 by inspection.
Qpsk constellation showing the effects of amplitude unbal. In active transmission, such as radio communication, active radar, etc. The original amplitude modulation is a family of modulation schemes, in which the amplitude of a. Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave. This lab introduces students to communications theory with amplitude modulation and demodulation. As we mentioned before, well use dsbc modulation because of its ease in demodulation. Here is the circuit used for modulation and its simulation. Ee4512 analog and digital communications chapter 6 the analytical signal for double sideband, large carrier amplitude modulation dsblc am is. All books are in clear copy here, and all files are secure so dont worry about it. Frequency division multiplexing, fdma amplitude modulation and demodulation. Quadrature amplitude modulation qam pam signals occupy. The resulting amplitude modulation am waveform is then demodulated using an envelope. Pdf in this paper, the digital algorithm and the device for the demodulation of the quadrature amplitude modulation signals are considered.
Basic principles of amplitude modulation figure 45 am signal containing not only the carrier and sidebands but also the modulating signal. 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. Amplitude modulation an overview sciencedirect topics. Amplitude modulation refers to the process in which amplitude of the carrier wave is varied with the message signal.
Rudolf unger, in handbook of geophysical exploration. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. Modulation and demodulation this chapter describes the essential principles behind modulation and demodulation, which. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. The purpose of this lab is for you to gain familiarity with the concepts of amplitude modulation and demodulation. Tuned circuits filter out the modulating signal and carrier harmonics, leaving only carrier and sidebands. 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. That could be the amplitude, phase, or frequency, which result in amplitude modulation am, phase modulation pm, or frequency modulation fm. Understanding quadrature demodulation radio frequency. Amplitude modulation is mostly used in the form of electronic communication. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. 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. Modulation is the process of altering the characteristics of the amplitude, frequency, or phase angle of the highfrequency signal in accordance with the instantaneous value of the modulating wave. Demodulation is defined as extracting the original informationcarrying signal from a modulated carrier wave.
The idea is simple, though the notion that it can be used to modulate signals. Modulation allows us to transmit multiple signals in the same medium i. In quadrature demodulation, we are converting the existing modulation into the corresponding iq baseband signals. Types of amplitude modulation am double sideband with carrier we will call it am. Once a signal has been modulated, information is retrieved through a demodulation process. In quadrature modulation, we use baseband iq signals to create an amplitude, frequency, or phasemodulated waveform that will be amplified and transmitted. This video uses properties of the fourier transform to explain modulation and demodulation inside a simple am radio system. Modulation and demodulation based interview questions and.
Amplitude modulation am, demodulation and their circuit. Demodulation is the process by which the original information bearing signal, i. Then inner products dot products are 1 1 0 can interpret inner product as projection of vector 1 v1 onto vector 2 v2in other words, inner product of v1 and v2 tells us how much of vector 1 is there in the direction of vector 2. This principle is at the heart of amplitude modulation. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. Note that this is on the very low end of the recommended voltage range.
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