It is a modulation system in which the signal is sampled at regular intervals and each sample is made proportional to the amplitude. Other is the pole amplitude modulation pam technique through which the windings are held in two sections per phase and reversing the current direction in one section of each phase with respect to the other. Pdf analog communication system pdf notes ac notes sw. The combined signal is transmitted over a frequency. Pulse amplitude modulation pam, quadrature amplitude modulation qam 12. This type of modulation technique is used in electronic communication. This principle is at the heart of amplitude modulation. Amplitude modulation was developed in the beginning of the 20th century. Modulation enables the transfer of information on an electrical signal to a receiving device that demodulates the signal to extract the blended. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. In this modulation, the amplitude of the carrier signal varies in accordance with the message signal, and other factors like.
Let us considered that the mmf distribution in the air gap of a three phase induction motor due to the stator winding carrying a three phase balanced currents can. Sampling theorem and pulse amplitude modulation pam. The method has considerable generality, but is particularly applicable to speed ratios not very different from unity. Amplitude modulation am, demodulation and their circuit. Modulation fm, amplitude shift keying ask, phase shift keying psk, etc. Amplitude of the modulated signal is proportional to the modulating signal the frequency is shifted from. There are no amplitude scales shown, but you should be able to deduce the depth. The concepts of amplitude modulation, modulation and demodulation, along with their differences is explained below. Effectively it is formed by having two carriers 90 out of phase. Principles of communication modulation tutorialspoint. 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.
Each conversation is shifted to a different part of the frequency spectrum by using a highfrequency waveform to carry each individual speech signal. 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. This technique applies the logic of amplitude modulation to the spacedistribution of the windings of an electrical machine. Principles of communication modulation a signal can be anything like a sound wave which comes out when you shout. The amplitude modulation am modulation depth figure is complementary to the modulation index. This lab gives you the opportunity to actually work on amplitude modulation and reinforce the theory taught in class. Pulse amplitude modulation pam in pulse amplitude modulation pam the amplitude of a train of constantwidth pulses is varied in proportional to the sample values of the modulating 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. Amplitude modulation simple english wikipedia, the free. Pulse width modulation and in position ppm, pulse position. Amplitude modulation in wind turbine noise valeri v.
Modulation is the process of putting information onto a high frequency carrier for transmission frequency translation. A carrier wave is modulated changed by adding audio. Square low fet amplitude modulator fet is nonlinear element. Analog communication pulse modulation tutorialspoint. The history of amplitude modulation brighthub engineering. In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. It was the earliest modulation technique used to transmit voice by radio. This shout can be heard only up to a certain distance. Amplitude modulation part 1 in class you have studied the theory of amplitude modulation. Here you can download the free lecture notes of analog communication system pdf notes ac notes pdf materials with multiple file links to download.
What is amplitude modulation, am electronics notes. The pam motor, in fact, differs from conventional ac induction motors only in its winding design. Let us considered that the mmf distribution in the air gap of a three phase induction motor due to the stator winding carrying a three phase balanced currents can be written as shown below. After continuous wave modulation, the next division is pulse modulation. The method of varying amplitude of a highfrequency carrier wave in accordance with the information to be transmitted, keeping the frequency and phase of the carrier wave unchanged is called amplitude modulation. In the process of amplitude modulation, the frequency and phase of the carrier remain constant whereas the maximum amplitude varies according to the instantaneous value of the information signal. Amplitude modulation refers to the process in which amplitude of the carrier wave is varied with the message signal. Modulationtypesamplitude,frequency,phase modulation. Amplitude modulation in analog communication amplitude modulation in analog communication courses with reference manuals and examples pdf. Here well use the example of a square law fet as illustrated in figure 9. Jan 01, 2012 single sideband amplitude modulation one method to produce signal sideband ssb amplitude modulation is to produce dsbam, and pass the dsbam signal through a band pass filter, usually called a single sideband filter, which passes one of the sidebands as illustrated in the diagram below. It requires that the amplitude of the dc a part of a t is equal to the amplitude of the ac part a.
A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. The first transmission however, was performed by fessenden in 1906 from brant rock, massachusetts. The bandwidth required for am system is twice the maximum frequency component of the modulating signal, which is an analogue signal. The pole amplitude modulation technique is explained in this article with the help of an example. For modulation index of 1, zoom around 0 hz to 5 khz to measure frequency of the demodulated message signal. Alternatively look into the early effect because this can also be used to create amplitude modulation. These form some of the main uses of amplitude modulation. Amplitude modulation am, variation of the amplitude of a carrier wave commonly a radio wave in accordance with the characteristics of a signal, such as a vocal or musical sound composed of audiofrequency waves. Learn the concise history of amplitude modulation or am broadcasting technique. Lenchine science and sustainability division, epa, gpo box 2607 adelaide sa 5001, australia abstract wind farms are gaining more and more popularity as a source of renewable energy. In pulse amplitude modulation pam technique, the amplitude of the pulse carrier varies, which is proportional to the instantaneous amplitude of. The fact that rapidly modulating the amplitude of one wave results in a waveform identical to playing two notes of different frequencies is quite remarkable and for more information on such wave interference, please see our wave interference and beat frequency demo.
Amplitude modulation, usually shortened to am, is a simple way to send a radio signal. Repeat step iii and step iv, for modulation index of 0, 0. Analog communication pdf notes book starts with the topics covering introduction ac, dsb modulation, ssb modulation, angle modulation concepts, angle modulation. Am is widely used for the transmission of data in everything from short range wireless links such as wifi to cellular telecommunications and much more. These might be operating with the transistor in the saturation region i. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. Glavieux a, thitimajshima p 2010 near shannon limit errorcorrecting pdf. To involve data information or speech information, another wave has to be imposed known as input signal above the carrier wave. Amplitude modulation in analog communication tutorial 22. We also see how to use a balanced mixer to modulate a signal. Typically the modulation depth is the amplitude modulation index expressed as a percentage. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion. Rc audio generator, oscilloscope, and spectrum analyzer demonstrations with speech and radio.
Varying these parameters in proportion to the baseband signal results in amplitude modulation am, frequency16 modulation fm, and phase modulation pm, respectively. Most radio systems in the 20th century used frequency modulation fm or amplitude modulation am for radio broadcast. Digital modulation eit, electrical and information technology. Apr 09, 20 modulation is a process through which audio, video, image or text information is added to an electrical or optical carrier signal to be transmitted over a telecommunication or electronic medium. You can publish your book online for free in a few minutes. So, step up the analysis and take into account nonlinearities. Demonstration with professor sandy hill from the university of massachusetts at amherst. This lab introduces students to communications theory with amplitude modulation and demodulation. The information is considered as the modulating signal and it is superimposed on the carrier wave by applying both of them to the. 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. Amplitude modulation can be produced in various ways. An original method of changing the speed of squirrelcage induction motors has recently been developed which enables efficient and economic operation to be obtained at either of two chosen speeds, using a single winding of standard type. In this chapter, let us discuss the following analog pulse modulation techniques. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation.
The end product of this pole amplitude modulation is an ac induction motor with two predetermined and distinct speeds 750 and 600 rpm in our example. Amplitude modulation circuit implementation electrical. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Nov 19, 2015 the resulting signal from the process of amplitude modulation is called amplitude modulation signal of simply am wave. 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. Amplitude modulation a continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. The first discovered a method for amplifying very weak signals and basically developed the amplitude modulation technique.
Farshad lahouti january 20, 2003 winter 2003 uw, ece 318 lecture notes 2 information source signal modulator propagation channel signal demodulator information destination analog communication system analog signals may be transmitted directly via carrier modulat ion over. Once this information is received, the low frequency information must be removed from the high frequency carrier. The signal can travel long distances, and appear in faraway places, because of the earths ionosphere. This process of imposing an input signal on a carrier wave is known as modulation. These high frequencies are called carrier frequencies. Amplitude modulation or am is a method to transmit signals via electromagnetic transmission. Amplitude modulation am plus frequency division multiplexing fdm is one way of solving above problem. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. Take a screenshot of output of the tlpf and output of the audio oscillator under the scope mode. Pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal.