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