It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. Ee4512 analog and digital communications chapter 6 the analytical signal for double sideband, large carrier amplitude modulation dsblc am is. The various types of modulation schemes presented in the literature can be obtained from these equations using appropriate definition for, v and v. Introduction to communication system, need for modulation, frequency division multiplexing, amplitude modulation, definition, time domain and frequency domain description. Jun 17, 2018 in this video, i have explained amplitude modulation by following outlines. It requires that the amplitude of the dc a part of a t is equal to the amplitude of the ac part a. 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 percentage modulation can be calculated using the formula. Surendra prasad, department of electrical engineering,iit delhi. Rc audio generator, oscilloscope, and spectrum analyzer demonstrations with speech and radio. Vary the modulating frequency and amplitude and observe the effects on the modulated waveform. Data loss is also more in amplitude modulation due to noise addition. The cyclic nature of alternating current enables the use of transformers, which use.
Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. Message signal embed into the amplitude of carrier simple am is also called. Note that this is on the very low end of the recommended voltage range. The high frequency carrier signal is mathematically represented by the equation 2. The depth of modulation can be varied using the variable knob provided at a. Indian institute of technology kanpur ee 381 electrical. Amplitude modulation refers to the process in which amplitude of the carrier wave is varied with the message signal. It was developed in the first few decades of the twentieth century. Quadrature amplitude modulation is widely used for carrying many digital signals, everything from wifi to mobile phone communications and very much more. Amplitude modulation can be accomplished by multiplying the carrier sine wave by a gain or attenuation factor that varies in accordance with the intelligence signal 2. The message signal xt is modulated by a carrier waveform ac cos2. Amplitude modulation am is a method of impressing data onto an alternatingcurrent ac carrier waveform. Because, atmospheric propagation is good for amplitude modulated signals.
Detection of combined frequency and amplitude modulation article pdf available in the journal of the acoustical society of america 926. Electrical power transmission is classified into two methods. Modulation theory 4 a sine wave is represented as follows ct ac cos2. Adding of noise for amplitude modulated signal will be more when compared to frequency modulated signals. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation.
Cw modulation is just a multiplication, for montone message and larger carrier. The highest frequency of the modulating data is normally less than 10 percent of the carrier frequency. When expressed as a percentage it is the same as the depth of modulation. Transmitter and receiver are simple in amplitude modulation. Amplitude modulation is mostly used in the form of electronic communication. It requires that the amplitude of the dc a part of at is equal to the amplitude of the ac part a. Peak amplitude is the height of an ac waveform as measured from the zero mark to the highest positive or lowest negative point on a graph. Amplitude modulation system a method for frequency translation frequency translation is a process which translates the original spectral range of a signal to a new spectral range by multiplying the signal with a sinusoidal signal. In practice, the carrier may be highfrequency hf while the modulation is audio.
Amplitude, frequency and phase modulation can be applied directly by software to the generated signals, which gives great flexibility where complicated and precise waveforms are required. Modulation is a process by which some characteristics of the carrier signal like its amplitude, frequency or phase are varied in proportion to message signal. The amplitude modulation receiver will be wider when compared to the fm receiver. Demonstration with professor sandy hill from the university of massachusetts at amherst. In amplitude modulation theory, the amplitude of a carrier signal is varied by the modulating voltage, whose frequency is invariably lower than that of the carrier. In other words, amplitude modulation allows the original carrier waveform through the vca, and also creates two new signals called the sum and the difference signals. Amplitude modulation an overview sciencedirect topics. Double sideband large carrier dsblc modultion for general message signal mt. Pdf analog communication system pdf notes ac notes sw. Complete notes download link ac notes analog communication pdf free download unit i introduction.
The original method of electronically encoding sound information on radio waves is called amplitude modulation, or am. Amplitude modulation early radio ee 442 spring semester. In this experiment, you will examine the characteristics of amplitude modulation am. As will be seen, it is the dc component which gives rise to the term at. 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. The cyclic nature of alternating current enables the use of transformers, which use magnetic principles to alter voltage levels.
In amplitude modulation, the message signal mt is impressed on the amplitude of the carrier signal ct a c cos2 f c t there are several different ways of amplitude modulating the carrier signal by mt each results in different spectral characteristics for the transmitted signal we will describe these methods, which are. The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier. Therefore, both fm and pm are often referred to as angle modulation. Bandwidths limit is also big advantage for amplitude modulation, which doesnt have in frequency modulation. This means that their ratio is unity at the output of the adder, which forces m to a. By driving a diode with sufficient ac voltage it acts like a switch. Lecture series on communication engineering by prof. Alternating current can be found in ac motor drives and long distance power transmission. Amplitude modulation theory frequency spectrum power. Phase modulation pm is a different form of frequency modulation and the carrier is similar in appearance to a frequencymodulated carrier. Dutton ee3 winter 2004 1 ee3 lab 1 amplitude modulation and demodulation 1 lab notes a word about power. Frequency modulation fm the process of combining the message signal with the carrier signal that causes the message signal to vary the frequency of the carrier signal. Amplitude modulation can be carried out by linearly combining the carrier and intelligence signals then applying the result to a nonlinear component or circuit.
This form of modulation is essentially derived from two carriers that are 90 out of phase and adding information, either analogue or digital. What is amplitude modulation, am electronics notes. Some harmonics can be larger than the fundamental component. Frenzeljr, in handbook of serial communications interfaces, 2016. Making use of this concept different modulation schemes have been. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. The carrier frequency, fc, should be larger than the highest spectral component. The modulated signal can be written as the sum of the unmodulated carrier wave. 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. Am is a relatively simple way to add audio information to a carrier wave so that sounds can be transmitted.
The fundamental voltage is proportional to the amplitude modulation index. Sinusoidal amplitude modulation am mathematics of the dft. Peaktopeak amplitude is the total height of an ac waveform as measured from maximum positive to maximum negative peaks on a graph. Calculate the total power and the ac and dc powers of the message signal. 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. In this video, i have explained amplitude modulation by following outlines. Amplitude modulation definition, types, solved examples.
Amplitude modulation is a modulation system in which the carrier wave has its. Amplitude modulation can be accomplished by multiplying the carrier sine wave by a gain or attenuation factor that varies in accordance with the intelligence signal. A carrier wave, after being modulated, if the modulated level is calculated, then such an attempt is called as modulation index or modulation depth. Analog communications lab manual pdf ac lab manual pdf. If the signal is bandlimited to the frequency range extending from a frequency f1 to f2 then after frequency. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Amplitudemodulation system a method for frequency translation frequency translation is a process which translates the original spectral range of a signal to a new spectral range by multiplying the signal with a sinusoidal signal. An interactive demo which enables you to both see and hear the result of multiplying a sine wave with a cosine amplitude envelope. In amplitude modulation, it is the voltage level of the signal to be transmitted. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. The effect of amplitude modulation index and frequency modulation index on total harmonic distortion in 1phase inverter to cite this article.
Amplitude modulation am the process of combining the message signal with the carrier signal and the two sidebands. The instantaneous amplitude overall signal power varies depending on the instantaneous amplitude of the modulating data. The message signal is, for example, a function of the sound to be reproduced by a. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. In this case ac is the power level of the carrier signal with no modulation therefore. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Signal waveform of amplitude modulation let the amplitude of the audio signal be mt a m cos. It states the level of modulation that a carrier wave undergoes. Amplitude modulated signal can be represented by the following equation.
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