Modulation and demodulation this chapter describes the essential principles behind modulation and demodulation, which. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. The second is to investigate classical analog amplitude modulation and the envelope detector. Modulation techniques lmodulation can be done by varying the l amplitude l phase, or l frequency of a high frequency carrier in accordance with the amplitude of the message signal. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which. Make sure that your program still compiles without. Principles of communication systems 20022003 8 chapter 7. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. Even for the pure tone modulation, the fm spectrum consists of an in nite number of sidebands. The idea is simple, though the notion that it can be used to modulate signals for transmission was hardly obvious before its discovery. There is no over modulation means that modulation index is less than or equal to 1.
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. Matlab code for amplitude modulation am file exchange. Some phase modulation and quadrature amplitude modulation formats have a higher spectral efficiency for data transmission than frequency shift keying, a form of frequency modulation. We consider binary modulation schemes and multilevel modulation schemes here. In analog case mt is an analog signal, whereas in digital case mt is a digital signal. In addition to reading the questions and answers on my site, i would suggest you to check the following, on amazon, as well. The most commonly used technique to detect and measure the modulation frequency is the socalled demon demodulation of noise processing 7, 10. Intro to generation of ask amplitude shift keying ask in the context of digital communications is a modulation. Amplitude modulation a continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. The two common forms of analog modulation are amplitude modulation. Pulse modulation timedivision multiplex tdm timedivision multiplexing is the method of combining several sampled signals in a definite time sequence. 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. Multiple choice questions and answers on modulation and.
Chapter 6modulation techniques shandong university. The heterodyne principle is the basic idea governing several different modulation schemes. Modulation index in modulation techniques a modulation index is usually defined such that it indicates how much the modulated variable varies around its original value. The time dependence of its projection onto the real axis gives the signal strength as drawn to the right of the corresponding phasor diagram. Amplitude modulation is a powerful tool that allows you to create and play new sounds that you cannot obtain using conventional oscillators alone. Modulation analog passband modulation, in the matlab library, the setup for this filename. The general form of a sinusoidal signal can be written as ft. Analog modulation techniques am modulation, fm modulation, single side band modulation, ssb, bandwith of fm signals, phase modulation, angle modulation, pdf file analog sinusoidal modulation analog sinusoidal modulation techniques, pdf file. Most radio systems in the 20th century used frequency modulation fm or amplitude modulation am for radio broadcast a modulator is a device that performs modulation. The measurement and definition of amplitude modulations. Phase modulation is another type of angle modulation very similar to frequency modulation. Digital modulation in digital communications, the modulation process corresponds to switching or keying the amplitude, frequency, or phase of a sinusoidal carrier wave according to incoming digital data three basic digital modulation techniques amplitude shift keying ask special case of. Residual amplitude modulation in laser electrooptic phase modulation article pdf available in journal of the optical society of america b 28.
There are many types of digital modulation techniques and also their combinations, depending upon the need. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. Amplitude modulation am is an analog modulation scheme where the amplitude a of. Frequency modulation is a type of angle modulation. The code for amplitude modulation am with control of modulation index ma has been developed using matlab according to conventional theory. Amplitude and frequencyphase modulation i always had di culties in understanding frequency modulation fm and its frequency spectrum. Amplitude modulation early radio ee 442 spring semester. 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.
Pdf residual amplitude modulation in laser electrooptic. Amplitude modulation am is a method of impressing data onto an alternatingcurrent ac carrier waveform. Amplitude modulation the amplitude of the carrier signal is controlled by the modulating signal pitfall of am. We begin our discussion of digital modulation by starting with the three basic types of digital modulation techniques. Multiple choice questions and answers on modulation and demodulation. Commutator determines the synchronization and sequence of the channels signals to be sampled. It is still in use today in a variety of systems, including, of course, am broadcast radio. Frenzeljr, in handbook of serial communications interfaces, 2016. 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 techniques amplitude modulation means that the carrier signal is modulated in proportion to. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. 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. Amplitude modulation is mostly used in the form of electronic communication.
Angle modulation changes the phase of a signal as well as its amplitude, where amplitude modulation leaves the phase unchanged. As illustrated in figure 5, the amplifier is biased class c and the output rf signal amplitude is modulated by causing the collector supply voltage to vary with the modulation voltage. Amplitude modulation definition, types, solved examples. In the case of amplitude modulation am, the modulated oscillation vector is always in phase with the carrier field while its length oscillates with the modulation frequency. Basic concepts of modulation three kinds of modulations modulation is the process of facilitating the transfer of information over a medium. The idea is simple, though the notion that it can be used to modulate signals. 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. When expressed as a percentage it is the same as the depth of modulation. Amplitude shift keying ask frequencyshift keying fsk phaseshift keying psk all of these techniques vary a parameter of a sinusoid to represent the information which we wish to send.
The instantaneous amplitude overall signal power varies depending on the instantaneous amplitude of the modulating data. There are many methods of generating am, and this experiment explores only. Amplitude modulation am is a modulation technique where the amplitude of a highfrequency sine wave. The demodulation is performed by an envelope detector. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. Amplitude modulation refers to the process in which amplitude of the carrier wave is varied with the message signal. Hence, digital modulation techniques have a greater demand, for their capacity to convey larger amounts of data than analog modulation techniques. The highest frequency of the modulating data is normally less than 10 percent of the carrier frequency. Free space optical using different modulation techniques. This principle is at the heart of amplitude modulation. Other methods of demodulating an am signal use synchronous techniques and provide. Amplitude modulation an overview sciencedirect topics.
Amplitude modulation, am, is one of the most straightforward ways of. The main difference between analog and digital modulation techniques is characterized by the message signal. 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. This is true even though everything we have discussed assumes that we have used simple sine waves as our input signals. For am this quantity is also known as modulation depth. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. In this code, it is considered the default value of ma equal to 1 for hundred percent modulation. Pulse amplitude modulation, pulse width modulation, pulse position modulation. In amplitude modulation, it is the voltage level of the signal to be transmitted. Even for the pure tone modulation, the fm spectrum consists of an in nite number of sidebands whose signs change from one sideband to the next one and whose amplitudes are given by the horrible bessel functions. Overmodulated am signals and its requirement for coherent detection are. The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier. To extend the range of sound, we need to transmit it through a medium other than air, such as a phone line or radio.
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