In this second experiment, we will examine the most common modulation scheme in daily life, namely, the. A carrier wave is purely made up of constant frequency, slightly similar to a sine wave. Build simple envelope detector for fm demodulation. Notice that the modulation index changes a lot with the modulation frequency from 2,500 to 5. The carrier amplitude is constant and the phase variation of the signal contains the information. Frequency modulation fm is the standard technique for highfidelity communications as is. Amplitude modulation early radio ee 442 spring semester. Indian institute of technology kanpur ee 381 electrical. Frequency modulation fm, as well as phase modulation pm, are types of angle exponential modulation. Build simple fm demodulator by using frequency discriminator. To study frequency modulation and determine its modulation factor. The m file will show these values in the matlab command window.
In this experiment, another widely used modulation technique will be introduced. I mean, i am not playing wav file, and i cannot just speed up its playback. This means that the bandwidth of the signal is 6x15 khz 90 khz on each side of the center frequency a. The specification for amplitude and frequency are given in the mfile.
Upon completion of the experiment, the student will. Its main advantage is that it is more resistant to additive noise than am. Explain the advantages and disadvantages of the different analog modulation techniques. Double sideband modulation dsb this experiment examines the characteristics of the doublesideband dsb linear modulation process. Frequencyshift keying fsk is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal. Frequency modulation and demodulation using ics 565, 8038 and 566 analog communications lab experiments series this series helpful to study and verify the characteristics and applications of analog communications circuits by conducting experiments. Slide 3 discretetime fm modulator slide 4 single tone fm modulation slide 5 single tone fm cont. Photonic measurement of microwave frequency based on phase modulation article pdf available in optics express 179. Modulation and demodulation pdf on the various aspects of modulation and demodulation.
It is still in use today in a variety of systems, including, of course, am broadcast radio. Theory shows that in order to transmit a wave effectively, the length of the. For the 15 khz signal, mf 5 and from table 1, we see that the frequency components are up high up to j6 and drop quickly afterwards. The second is to investigate classical analog amplitude modulation and the envelope detector. In frequency modulation fm, unlike am, the amplitude of the carrier is kept constant, but its frequency is altered in accordance with variations in the audio signal being sent. Pdf photonic measurement of microwave frequency based on.
This form of modulation was developed by the american electrical engineer edwin h. Exercise 51 generating ssb signals by the filter method 91. The frequency of a radiofrequency channel can be explained best as the frequency of a carrier wave. It does not carry much information that we can relate to data or speech. In this second experiment, we will examine the most common modulation scheme in daily life.
This article is concerned with the detection of mixed modulation mm, i. The instantaneous frequency of the modulated signal is. Ece 4670 spring 2014 lab 5 frequency modulation, demodulation. This chapter describes the essential principles behind modulation and demodulation, which we introduced briefly in chapter 10. As we have seen in this document, frequency modulation can be simplified to angle modulation with a simple integrator. The technology is used for communication systems such as telemetry, weather balloon radiosondes, caller id, garage door openers, and low frequency radio transmission in the vlf and elf bands. Slide 6 narrow band fm slide 7 bandwidth of an fm signal slide 8 demod. Using the bessel function table see back page of this lab, calculate the magnitude of the carrier and the first four sidebands that appear in the fm waveform.
Hapter modulation and demodulation mit opencourseware. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. Frequency modulation objectives upon completion of this chapter, the student should be able to. Therefore, both fm and pm are often referred to as angle modulation. In analog applications, the carrier frequency is varied in direct proportion to changes in the amplitude of an input signal. Amplitude modulated signal can be represented by the following equation. The phase of the carrier wave is also kept constant. Amplitude modulation am is a modulation technique where the. The modulating signal contains the intended message or information sometimes consisting of audio data, as in am radio. Experiment 5 frequency modulation 1 objective to understand the principles of frequency modulation and demodulation. With at being maybe nonperiodic, its maybe frequency modulation. The use of the quadrature detector andor the phaselocked loop for fm demodulation is also considered.
Frequency modulation and demodulation using ics 565, 8038. Now carefully repeat this experiment with the highfrequency. Objectives 1 learn about vco and how it can be calibrated 2 learn how to generate fm signal using vco 3 display and measures of fm spectrum equipment required. The subject is new and all of its ramifications and prob lems are not known as yet, hence this volume of compara tively few pages is not intended as a complete exposition of the subject. The use of the quadrature detector andor the phaselocked loop for. Phase modulation, and frequency modulation are both the modulation techniques analyzed in angle modulation. In frequency modulation, the amplitude of the carrier wave is kept constant but its frequency is varied in accordance with the amplitude of the audio frequency signal. The factor 2 in the equation is to account for both the upper and lower sidebands left and. To understand the theoretical foundations for angle modulation as well as frequency modulation fm and demodulation to implement the simulink models for fm including a basic sinusoid and a multimedia file music to analyze each signal in time and frequency domains using time scope and spectrum analyzer. Chapter 8 frequency modulation fm fm was invented and commercialized after am. Frequency modulation frequency modulation is the process by which frequency of the carrier signal ct changes with respect to the modulating signal mt. Analog communications lab manual pdf ac lab manual pdf.
Frequency modulation fm is an important modulation scheme both because of its widespread commercial use, and because of its simplicity. The mfile will show these values in the matlab command window. Frequency modulation, or fm, is an important method of impressing information on a carrier. The specification for amplitude and frequency are given in the m file. Calculate modulation index, signal bandwidth, sideband frequencies and.
Write a mathematical expression for fourier transform of a di. Fm modulated signal st is a nonlinear function of the modulating signal mt, thus it is known as nonlinear modulation process. If you have the time, take a look at the theory behind phaselocked loops pll, as in pp. Discuss the differences between am and angle modulation. Pdf detection of combined frequency and amplitude modulation. Amplitude modulation matlab tutorial amplitude modulation in. For example, the signal in a cell phone is a voice signal with a. The concepts of amplitude modulation, modulation and demodulation, along with their. First, since fm only changes the frequency and not the amplitude of the carrier w ave, fm receivers can be built to ignore amplitude voltage changes. All books are in clear copy here, and all files are secure so dont worry about it. The demodulation is performed coherently and its strict requirement for a perfect synchronization to the carrier is discussed. For the lowfrequency signal generator, this is equivalent to setting channel a to a 2v amplitude with 30khz frequency, and setting.
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. As its name implies, frequency modulation fm uses a messages amplitude to vary the frequency of a carrier instead of its amplitude. In this experiment, you will examine the characteristics of amplitude modulation am. This means that the fm demodulator is designed to look for changes in frequency instead. This site is like a library, you could find million book here by using search box in the header. These are covered in chapter 5 of 2, or chapter 3 of 1. Frequency modulation is a form of modulation, which represents information as variations in the instantaneous frequency of a carrier wave. As a 250 mvpp amplitude of audio signal is applied to the carrier signal, the percentage modulation is set to 50% by adjusting the vr1. Instantaneous frequency the instantaneousfrequencyof cos. Phase modulation pm is a different form of frequency modulation and the carrier is similar in appearance to a frequencymodulated carrier.
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