Amplitude modulation consists encoding information onto a carrier signal by varying the amplitude of. Communication is a process of conveying information at a distance. Am power issue revisited lengthy read k4kyv, sep 17, 2017. Here we explain the amplitude modulation process using a sinusoidal signal as the modulating signal. This is the most widely used type of am modulation. The size of the antenna depends inversely on the frequencies present in the message, and voice and music have relatively low frequencies. Am modulator is one which is used for superimposing a low frequency signal on a high frequency carrier signal. Balanced modulator an amplitude modulator that can be adjusted to control the amount of modulation. Q1 the maximum power efficiency of an am modulator is. Mixer an electronic circuit that combines two frequencies. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. Design and implementation of amplitude modulator and demodulator introduction communication is the most important needs from the very beginning of civilization. Amplitude modulation index an overview sciencedirect topics.
Adjust the vr1 of am modulator to get maximum amplitude of am. So this time, instead of having one set of harmonics modulating. Amplitude modulation is done by a circuit called modulator. In commercial tv transmission in india, picture and speech signals are. Use the spectrum analyzer to compare this modulator to the one in part 2. 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. 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. The receivers used to listen to amdsbc are perhaps the simplest receivers of any radio modulation technique. Am has only two sidebands usb and lsb and the bandwidth was found. The modulation index is an important parameter in am. Pdf one of the problems that often arise in the conversion process using an inverter is the existence of total harmonic distortion thd. Slide 6 narrow band fm slide 7 bandwidth of an fm signal slide 8 demod. A signal 2cos104 volts is applied to an fm modulator with the sensitivity constant of 10 khzvolt.
Explain briefly in your report how amplitude modulation is accomplished by this circuit. 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. The output from the modulator is added to an offset amplitude value. Amplitude modulation definition of amplitude modulation. Using the oscilloscope, observe the output signals for the audio amplitudes of 200 mvpp and 150 mvpp. It is strongly suggested that you examine your text book for other methods. Dec 21, 2017 amplitude modulation is one of the earliest radio modulation techniques. Now lets look at the effect of the modulation index. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. The original method of electronically encoding sound information on radio waves is called amplitude modulation, or am. Typically the modulation depth is the amplitude modulation index expressed as a percentage.
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. 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. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Additive synthesis, amplitude modulation and frequency. Q2 consider sinusoidal modulation in an am systems, assuming no. Types of amplitude modulation am double sideband with carrier we will call it am. Am is a relatively simple way to add audio information to a carrier wave so that sounds can be transmitted. Materi amplitude modulation am linkedin slideshare. 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. Amplitude modulation an overview sciencedirect topics. An interactive demo which enables you to both see and hear the result of multiplying a sine wave with a cosine amplitude envelope. What is am modulation amplitude modulation need of.
To learn what is happening inside the tims modules by use of mc1496 to. Modulation index is basically the ratio of amplitude of the massage signal the message we want to transmit to the amplitude of carrier signal. The application of these pulses to the tuned tank circuit will give amplitude modulation. 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. Draw the phase representation of an amplitude modulated wave. The modulation index is more than 1 here, so it is the case of over modulation. Ee4512 analog and digital communications chapter 6 the analytical signal for double sideband, large carrier amplitude modulation dsblc am is. The modulation index m defines the power efficiency but m must be less than 1. Detailed explanation of am modulation amplitude modulation, its working principle, and basic need of modulation. 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. Slide 6 narrow band fm slide 7 bandwidth of an fm signal. 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 modulation index in the output signal will be a 0 b 3 c 9 d 27 gate 1996. 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.
Let us understand modulation index in am amplitude modulation. Understanding the waveform and frequency spectrum of am signal and calculating the percent of modulation. Am modulator and demodulator by the use of mc1496 goal. This is the same as the am modulation above but without the carrier. Fm signals have the same peak frequency deviation, then. Am was the first widespread technique used in commercial. 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. Pdf the effect of amplitude modulation index and frequency. The basic theory and equations behind amplitude modulation are relatively straightforward and can be handled using straightforward trigonometric calculations and manipulation. Turn the power supply on and capture the am signal and its spectrum by executing timefreq. Practical circuitry is more likely to use a modulator, rather than the more idealised multiplier. Carrier signal is the higher frequency wave with higher energy to carry the message signal to long dis.
The receivers used to listen to am dsbc are perhaps the simplest receivers of any radio modulation technique. 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. In amplitude modulation, the amplitude of the carrier is varied in accordance with the information signal. Using the fft, observe and record the output signal spectrum.
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. Amplitude modulation am is an analog modulation scheme where the amplitude a of. Message power in st slide 6 powers in single tone case cont. In am schemes, the modulation index refers to the amplitude ratio of the. Am modulators base, collector, grid and plate modulators. The modulation index is ratio of modulating signal voltagevm to the carrier voltagevc.
Nov 16, 2019 amplitude modulation with modulation factor 1 or 100%. Slide 3 discretetime fm modulator slide 4 single tone fm modulation slide 5 single tone fm cont. Two common methods by which information is encoded on radio signals, amplitude. The modulation index m defines the power efficiency but. Measuring the modulation index of an am signal using an. The demodulation is performed by an envelope detector.
It was developed in the first few decades of the twentieth century. One of the principal techniques used in electronic communication is. So remember, if a modulation index is used, the signal must be shifted based on the maximum amplitude of mx bb, not x bb. We looked at am timedomain waveforms in the previous page. 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. Remember, for analysis purposes keep the modulation index and frequency the same as part 2, step 3. The two main differences of am with respect to dsb signals are the presence of a carrier component and that the envelope. If the distance is involved is beyond direct communication, electronic communication comes into the picture. Problem 3 the output signal from an am modulator is. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. What is modulation index modulation index in am and fm. In other words, this harmonic is being amplitude modulated by the changing action of the filter. Download pdf introduction in am schemes, the modulation index refers to the amplitude ratio of the modulating signal to the carrier signal.
In this modulator the amplitude of a carrier is varied in accordance with instantaneous value of message signal. In this application note, we are going to show a convenient method. A method of transmitting signals, such as sound or digital information, in which the value of the signal is given by the amplitude of a. Communication systemsamplitude modulation wikibooks, open. With the help of fastfouriertransforms fft, the modulation index can be obtained by measuring the sideband amplitude and the carrier amplitude.
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. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Amplitude modulation index an overview sciencedirect. Overmodulated am signals and its requirement for coherent detection are also considered. 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. The modulation index m is an indicator for the degree of the amplitude modulation and is sometimes indicated in percent. Doublesideband dsb an amplitude modulated signal in which the carrier is suppressed, leaving only the two sidebands. Carrier signals properties can be adjusted pushing sine button. Here was the final plot baseband in red, am waveform in blue. Process by which a property or a parameter of a signal is varied in proportion to a second signal. 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. In fact, all radio channels in the am band use this type of modulation. Analog communication am modulators in this chapter, let us discuss about the modulators, which generate amplitude modulated wave.
288 1467 1209 1415 604 1122 547 1244 588 883 1241 1083 1103 953 670 35 319 53 1102 595 482 1053 1092 165 1444 853 861 1064 917 1478 144 1327