Ee4512 analog and digital communications chapter 6 the analytical signal for double sideband, large carrier amplitude modulation dsblc am is. Slide 6 narrow band fm slide 7 bandwidth of an fm signal slide 8 demod. In other words, this harmonic is being amplitude modulated by the changing action of the filter. Data 10110100 dengan bit rate 1 bps, f 4 hz, a0 1 dan a14 teknik modulasi am modulasi basis modulasi basis adalah metode memodulasi amplitudo dimana sinyal carier dan sinyal informasi samasama dilewatkan melalui sisi basis modulator am modulator am yang digunakan berkomponen utama transistor sehingga sinyal termodulasinya. In commercial tv transmission in india, picture and speech signals are. Understanding the waveform and frequency spectrum of am signal and calculating the percent of modulation. Recall, the bandwidth of a complex signal like fm is the difference between its highest and lowest frequency components, and is expressed in hertz hz. Amplitude modulation contents slide 1 amplitude modulation slide 2 the envelope and no overmodulation slide 3 example for single tone modulation slide 4 measuring the modulation index slide 5 transmitted vs. Pdf one of the problems that often arise in the conversion process using an inverter is the existence of total harmonic distortion thd.
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. What is am modulation amplitude modulation need of. Dec 21, 2017 amplitude modulation is one of the earliest radio modulation techniques. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. Here we explain the amplitude modulation process using a sinusoidal signal as the modulating signal. Amplitude modulation am is an analog modulation scheme where the amplitude a of. Explain briefly in your report how amplitude modulation is accomplished by this circuit. Since carrier is suppressed, so am 0, and thus m am. The modulation index is more than 1 here, so it is the case of over modulation. Remember, for analysis purposes keep the modulation index and frequency the same as part 2, step 3. Mixer an electronic circuit that combines two frequencies.
Q1 the maximum power efficiency of an am modulator is. Nov 16, 2019 amplitude modulation with modulation factor 1 or 100%. In fact, all radio channels in the am band use this type of modulation. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process.
Here was the final plot baseband in red, am waveform in blue. Am receivers are very susceptible to noise 2 noise immunity can be improved by increasing the frequency deviation no such option exists in am 3 bandwidth requirement is greater and depends upon modulation index bandwidth is less than fm or pm and doesnt depend upon a modulation index 4 fm or pm transmitters and. The two main differences of am with respect to dsb signals are the presence of a carrier component and that the envelope. Typically the modulation depth is the amplitude modulation index expressed as a percentage. Amplitude modulation an overview sciencedirect topics. Overmodulation overmodulation is a condition that occurs when an excessive intelligence signal overdrives an am modulator making %m 100% because e i e c modulated carrier amplitude reach value greater than double of unmodulated value it produces a distortion known as sideband splatter, which results on transmission at frequencies outside. Let us understand modulation index in am amplitude modulation. Download pdf introduction in am schemes, the modulation index refers to the amplitude ratio of the modulating signal to the carrier signal. Types of amplitude modulation am double sideband with carrier we will call it am.
Depending upon the width of the modulation the maximum amplitude a 2 of the modulator the same is true to a greater or lesser extent for all the other harmonics within the signal. Carrier signal is the higher frequency wave with higher energy to carry the message signal to long dis. As an example of how to accomplish this doubling of inverter frequency, an analysis of a sevenlevel diodeclamped inverter with an amplitude modulation index of 0. Using the fft, observe and record the output signal spectrum. The original method of electronically encoding sound information on radio waves is called amplitude modulation, or am. So this time, instead of having one set of harmonics modulating. Design and implementation of amplitude modulator and demodulator introduction communication is the most important needs from the very beginning of civilization.
Problem 3 the output signal from an am modulator is. It was developed in the first few decades of the twentieth century. Am has only two sidebands usb and lsb and the bandwidth was found. Am was the first widespread technique used in commercial. Turn the power supply on and capture the am signal and its spectrum by executing timefreq. Communication is a process of conveying information at a distance. Adjust the vr1 of am modulator to get maximum amplitude of am.
The maximum power efficiency of an am modulator is a 25% b 50%. In this modulator the amplitude of a carrier is varied in accordance with instantaneous value of 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. In am schemes, the modulation index refers to the amplitude ratio of the. Amplitude modulation definition of amplitude modulation. Modulation index is basically the ratio of amplitude of the massage signal the message we want to transmit to the amplitude of carrier signal. Amplitude modulation consists encoding information onto a carrier signal by varying the amplitude of. The modulation index m is an indicator for the degree of the amplitude modulation and is sometimes indicated in percent.
From vintage tubebased gear, to military surplus, to modern, ultraefficient fetbased class e transmitters, amplitude modulation am offers the experimenter, homebrewer, and radio restoration buff great opportunities to learn, build, and enjoy radio. Am modulator is one which is used for superimposing a low frequency signal on a high frequency carrier signal. The basic theory and equations behind amplitude modulation are relatively straightforward and can be handled using straightforward trigonometric calculations and manipulation. The modulation index m defines the power efficiency but. Additive synthesis, amplitude modulation and frequency. During the first cycle, the reference waveform is centered in the upper three carrier bands, and during the next cycle, the reference waveform is centered in the lower three carrier bands as shown in fig. To learn what is happening inside the tims modules by use of mc1496 to. Amplitude modulation is one of the earliest radio modulation techniques.
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 communication systems arose from the need to send an acoustic signal, the message, over the airwaves using a reasonably sized antenna to radiate it. Understanding the principle of amplitude modulation am. Slide 6 narrow band fm slide 7 bandwidth of an fm signal.
Percentage modulation is equal to m multiplied by 100%. The receivers used to listen to am dsbc are perhaps the simplest receivers of any radio modulation technique. Communication systemsamplitude modulation wikibooks. An interactive demo which enables you to both see and hear the result of multiplying a sine wave with a cosine amplitude envelope. Figure 7 labview vis that you need to complete the am modulation and demodulation block diagram below figure 8 completed am modulation and demodulation block diagram am demodulation. One of the principal techniques used in electronic communication is. Data 10110100 dengan bit rate 1 bps, f 4 hz, a0 1 dan a14 teknik modulasi am modulasi basis modulasi basis adalah metode memodulasi amplitudo dimana sinyal carier dan sinyal informasi samasama dilewatkan melalui sisi basis modulator am modulator am yang digunakan berkomponen utama transistor sehingga sinyal. Process by which a property or a parameter of a signal is varied in proportion to a second signal. We looked at am timedomain waveforms in the previous page. Communication systemsamplitude modulation wikibooks, open. In radio communications, single sideband modulation ssb or single sideband suppressedcarrier modulation ssbsc is a type of modulation used to transmit information, such as an audio signal, by radio waves.
Fm signals have the same peak frequency deviation, then. Doublesideband dsb an amplitude modulated signal in which the carrier is suppressed, leaving only the two sidebands. Am modulators base, collector, grid and plate modulators. This is the same as the am modulation above but without the carrier.
Draw the phase representation of an amplitude modulated wave. Am is a relatively simple way to add audio information to a carrier wave so that sounds can be transmitted. Measuring the modulation index of an am signal using an. Practical circuitry is more likely to use a modulator, rather than the more idealised multiplier. The modulation index is an important parameter in am. In this application note, we are going to show a convenient method. Amplitude modulation a1 49 you will see in this experiment, and in others to follow, that there is no problem in generating an am signal with a depth of modulation exceeding 100%, and without. Analog communication am modulators in this chapter, let us discuss about the modulators, which generate amplitude modulated wave. It is strongly suggested that you examine your text book for other methods. A signal 2cos104 volts is applied to an fm modulator with the sensitivity constant of 10 khzvolt. The modulation index m defines the power efficiency but m must be less than 1.
Use the spectrum analyzer to compare this modulator to the one in part 2. With the help of fastfouriertransforms fft, the modulation index can be obtained by measuring the sideband amplitude and the carrier amplitude. Using the oscilloscope, observe the output signals for the audio amplitudes of 200 mvpp and 150 mvpp. In reality the terms am modulation index and the am modulation depth are often used interchangeably, so there are often no hard and fast rules regarding their use. If the distance is involved is beyond direct communication, electronic communication comes into the picture. Slide 3 discretetime fm modulator slide 4 single tone fm modulation slide 5 single tone fm cont. Detailed explanation of am modulation amplitude modulation, its working principle, and basic need of modulation. The modulation index in the output signal will be a 0 b 3 c 9 d 27 gate 1996.
So remember, if a modulation index is used, the signal must be shifted based on the maximum amplitude of mx bb, not x bb. Amplitude modulation index an overview sciencedirect. This is the most widely used type of am modulation. The modulation index is ratio of modulating signal voltagevm to the carrier voltagevc. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Pdf the effect of amplitude modulation index and frequency. When modulation index is more than 1 over modulation then detection is possible only with, synchronous modulation, such signal can not be detected with envelope detector.
Message power in st slide 6 powers in single tone case cont. Q2 consider sinusoidal modulation in an am systems, assuming no. Two common methods by which information is encoded on radio signals, amplitude. The demodulation is performed by an envelope detector. Carrier signals properties can be adjusted pushing sine button. Materi amplitude modulation am linkedin slideshare. To have example of fm modulation index, take sm5074 or sm5075, and apply external modulating signal say 1 khz with certain amplitude, the fm modulated signal when viewed in analog digital oscilloscope e. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. The message signal is, for example, a function of the sound to be. Overmodulated am signals and its requirement for coherent detection are also considered. Balanced modulator an amplitude modulator that can be adjusted to control the amount of modulation. The output from the modulator is added to an offset amplitude value. C67 dsk implementation using cc for this part of the lab, you will demodulate the am signal generated by the arbitrary waveform generator on your lab bench.
In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Am modulator and demodulator by the use of mc1496 goal. The application of these pulses to the tuned tank circuit will give amplitude modulation. The size of the antenna depends inversely on the frequencies present in the message, and voice and music have relatively low frequencies.
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