Amplitude modulation am is a modulation technique used in electronic communication, most. Pulse amplitude modulation pam, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. Communications i amplitude modulations and demodulations. 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. The message signal is, for example, a function of the sound to be reproduced by a. The demodulator is composed of a lowpass filter, whose cutoff frequency is slightly. To study and perform pulse amplitude modulation and demodulation. 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.
Unicamp university of campinas, state of sao paulo pdf. To study and perform frequency modulation and demodulation. The second is to investigate classical analog amplitude modulation and the envelope detector. Here well use the example of a square law fet as illustrated in figure 9. Amplitude modulation am, demodulation and their circuit. Modulation and demodulation pdf on the various aspects of modulation and demodulation. Demodulation is extracting the original informationbearing signal from a carrier wave. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors.
Amplitude modulation can be produced in various ways. 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 to do, using the gain control g of the adder. The amplitude modulated wave form, its envelope and its frequency spectrum and bandwidth. Fundamentals of amplitude modulation and demodulation. 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. This gives us something to modulate and carry the information pattern from. The demodulation is performed by an envelope detector.
Note that this is on the very low end of the recommended voltage range. 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. It is specifically designed to stir the interest of junior or senior level electronics minded electrical. Amplitude modulation and demodulation 1 lab notes a word about power. Analog modulation and demodulation amplitude modulation pages 306309. Restoring or recovering the message signal from the received modulated waveform that is generally corrupted by noise. Process by which a property or a parameter of a signal is varied in proportion to a second signal.
In this chapter we will discuss ways of demodulating am, cw, fm, phase, and pulse modulation. 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. Introduction to iq demodulation of rfdata september 15, 1999 page 3 of 1 introduction 1. Feb 12, 2014 demodulation is performed by detecting the amplitude level of the carrier at every symbol period. Figure 321 includes a simplified circuit view a for this demodulator and its waveforms views b and c. Amplitude shift keying ask modulation code in matlab amplitude shift keying is one of the basic types of digital modulation techniques. To understand the theoretical foundations of analog communications as well as of doublesideband amplitude modulation and demodulation dsbam. To study and perform phase shift keying 10 modulation and.
To study and perform pulse width modulation and demodulation. 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. Yet, am continues to be used today in many communication applications. To study and perform pulse position 6 to study and perform pulse code modulation and demodulation. Sampling theorem determines the necessary conditions which allow us to change an analog signal to a discrete one. Learn about the most straightforward way of encoding information in a carrier waveform. When expressed as a percentage it is the same as the depth of modulation. Amplitudefrequency modulation communication system. Both phase and frequency of carrier are known at the demodulator amplitude of. Analog communication fm demodulators in this chapter, let us discuss about the demodulators which demodulate the fm wave.
Experiment 5 frequency modulation 1 objective to understand the principles of frequency modulation and demodulation. A modem is an equipment that performs both modulation and demodulation. Load file, prefiltering, modulation, demodulation and. It is still in use today in a variety of systems, including, of course, am broadcast radio. The responses are compared against the theoretical. Fig a sinosoidal modulation signal bhigh frequency carrier c. We will add additional functions to build the am demodulator. Amplitude modulation and demodulation objective amplitude modulation am is one of the simplest methods for modulating a sinusoidal carrier wave. Amplitude shift keying ask modulation code in matlab. Hi, im a beginner in matlab and im just wondering whether the modulation constant. 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. Sampling theorem and pulse amplitude modulation pam.
Amplitude modulation is the changing the amplitude of the carrier signal with respect to the instantaneous change in message signal. Pulsecode modulation pcm is a method used to digitally represent sampled analog signals. 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. To study and perform amplitude modulation and demodulation. Pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. Pulse amplitude modulation is widely used in baseband transmission of digital data, with nonbaseband applications having been largely superseded by pulsecode modulation, and, more recently, by pulse position modulation. Pulseamplitude modulation pam, is a form of signal modulation where the message. Pulse width modulation and in position ppm, pulse position.
An am wave may thus be dscribed, in the most general form, as a function of time as follows. Each channel sharing scheme a set of basis vectors. Amplitude modulation and demodulation 2017 frank dorenberg n4spp v1. Introduction what is communication transmitter channel receiver a communication system process of conveying message or information transmitter modifies the message signal into a form which is suitable for transmission over channel which is achieved by modulation information source. When we do not use modulation, the system is called a baseband communication system. Amplitude modulation am is an analog modulation scheme where the amplitude a of.
In frequency modulation, the amplitude of the carrier. Amplitude modulation a continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Hapter modulation and demodulation mit opencourseware. It requires that the amplitude of the dc a part of a t is equal to the amplitude of the ac part a. Sampling theorem and pulse amplitude modulation pam reference stremler, communication systems, chapter 3. In a pcm stream, the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Modulation and demodulation this chapter describes the essential principles behind modulation and demodulation, which.
However its presence provides a simple means of demodulation using envelope. Typical modulation system the reverse process is called demodulation. The basic theory and equations behind amplitude modulation are relatively straightforward and can be handled using straightforward trigonometric calculations and manipulation. 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. 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. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. Double sideband suppressed carrier dsb sc modulation. Therefore, when we receive the amplitude modulation signal, we need to restore the audio signal. The am diode detector can be built from just a diode and a few other components and as a result it is a very low cost circuit block within an overall receiver. This chapter describes the essential principles behind modulation and demodulation, which we introduced briefly in chapter. Introduction frequency modulation is a form of modulation, which represents information. Then, students will use labview to program an am demodulator and use it to explore and visualize the. 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.
Restoring or recovering the message signal from the received modulated waveform that is generally corrupted by noise types of am detectors. We have seen that rf modulation is simply the intentional modification of the amplitude, frequency, or phase of a sinusoidal carrier signal. In the doublesideband suppressedcarrier transmission dsb sc modulation, unlike am, the wave carrier is not transmitted. This principle is at the heart of amplitude modulation. The circuit in which restoration is achieved is called the detector or demodulator both of these terms are used in neets. The term demodulator is used because the demodulation process is considered to be the opposite of modulation. In practice, the demodulation of suppressed carrier amplitude modulated signals requires fairly. Why modulation is used suitable for signal transmission distanceetc. 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. Bandpass modulation and demodulation, communications link analysis, channel coding, modulation and. There are many types of modulation so there are many.
Cr1 is the input diode which allows capacitor c1 to charge to the peak value of the pam input pulse. 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. Is there a way i can vary it, say, to 100% modulation depth. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. From experiment 3, we know that the amplitude modulation signal utilizes the amplitude of audio signal to modulate high frequency carrier signal. Matlab code for amplitude modulation am file exchange. Modulation recognition using artificial neural networkann. What is digital modulation and state various techniques. In this code, it is considered the default value of ma equal to 1 for hundred percent modulation. Ee4512 analog and digital communications chapter 6 the analytical signal for double sideband, large carrier amplitude modulation dsblc am is. Ee4512 analog and digital communications chapter 6 chapter 6 analog modulation and demodulation amplitude modulation pages 306309.
What we do in am, very roughly,is to throw away the frequency content of. 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. Now i project onto m and onto n to get back the numbers. 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. When the modulator and the demodulator are located in the same apparatus, the system is called a modem modulator, demodulator. There are no amplitude scales shown, but you should be able to deduce the depth of modulation 1 by inspection. Finally, the significance of an adequate demodulator bandwidth is highlighted during highspeed. Explain generation and demodulation of pam, ppm and pwm with waveforms. However, each word in this system indicates the difference in amplitude, positive or negative, between this. It is an analog pulse modulation scheme in which the amplitudes of a train of carrier pulses are varied according to the sample value of the message signal. 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 modification is performed according to a specific scheme that is. What is analog modulation and state various techniques.
This lab introduces students to communications theory with amplitude modulation and demodulation. Capacityapproaching codes demodulation line coding modem anm pom. The idea is simple, though the notion that it can be used to modulate signals. Laboratory manual principles of communication system lab ee226f ivth semester. Modulation is a technique to transmit information via radio carrier waveform.
Amplitude modulation or am is a method to transmit signals via electromagnetic transmission. Frequency demodulation matlab fmdemod mathworks india. To improve the spectral efficiency of the amplitude modulation, two schemes can be used to either utilize or remove the 100% spectra redundancy. If not, what is the default depth of modulation for am here. Use your project files from the previous fir laboratory. Analog communication fm demodulators tutorialspoint. Explain generation and demodulation of pam, ppm and pwm. The diode detector is the simplest and most basic form of amplitude modulation, am signal detector and it detects the envelope of the am 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. Theory shows that in order to transmit a wave effectively, the length of the. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications.
If we were to implement every possible combination of demodulation algorithm, carrierrecovery technique, and clock regeneration as a distinct model, the combinatorial explosion of different models would become unmanageable. The process of amplitude modulation consists of the amplitude of the carrier wave being varied in sympathy with a modulating signal. Pulse amplitude demodulation peak detection is used to detect pam. The code for amplitude modulation am with control of modulation index ma has been developed using matlab according to conventional theory. 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. Overmodulated am signals and its requirement for coherent detection are also considered. The purpose of this lab is for you to gain familiarity with the concepts of amplitude. First, students will generate an am signal using data from a file, and then they will use the envelope detector method to recover the original message by connecting the am signal to a rectifier and the. Singlesideband ssb modulation, which removes either the lsb or usb so that for one message signal mt, there is only a bandwidth of b hz quadrature amplitude modulation qam, which. At that time, the baseband signal is transmitted directly.
Amplitude modulation early radio ee 442 spring semester. In theory the total integrated noise approaches zero as the filter bandwidth goes to zero. It is a nonlinear process that generates additional frequencies, as we will see. Application note of pampulse amplitude modulation signal. The ideal modulated signal should have a minimum euclidean distance of 2.
Using matlab m file and simulink to implement fm modulation and demodulation. Oct 30, 2017 amplitude modulation and demodulation. This chapter describes the essential principles behind. The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier.