The idea is simple, though the notion that it can be used to modulate signals for transmission was hardly obvious before its discovery. There are no amplitude scales shown, but you should be able to deduce the depth. If amplitude is the only parameter of the carrier wave to be altered by the information signal, the modulating method is called amplitude shift keying ask. Theoretical and experimental comparison of amplitude modulation techniques for parametric loudspeakers. Keying is indicating the transmission of digital signal over the channel. If amplitude is the only parameter of the carrier wave to be altered by the information signal, the modulating method is called amplitudeshift keying ask. Jun 17, 2018 in this video, i have explained amplitude modulation by following outlines. The spectrum of the modulated signal yt can be found by using the modulation property of the fourier transform.
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. As for the mechanism, when amplitude modulation is used there is a variation in the amplitude of the carrier. 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. This is further divided into frequency and phase modulation. The demodulation is performed by an envelope detector. Angle modulation is the process in which the frequency or the phase of the carrier varies according to the message signal. Amplitude modulation, modulators, and demodulators ese. There is another way of modulating a, sinusoidal carrier wave, namely, angle modulation in which the angle of the carrier wave is varied according to the baseband signal. It is also referred as binary amplitude shift keying bask as its usual operation is associated with only two levels.
Note that this is on the very low end of the recommended voltage range. Lowers amplifier gain when strong signal amplitude is present to keep transducer output constant avoids having to adjust the volume control for weak vs strong signals needed because signal strength can vary due to many factors such as. Amplitude modulation is defined as the process in which the amplitude of the carrier wave ct is varied about a mean value, linearly with the baseband signal. This method is capable of producing nearly 100% modulation with reasonable linearity. Frenzeljr, in handbook of serial communications interfaces, 2016. In an ask system, the binary symbol 1 is represented by transmitting a fixedamplitude carrier wave and fixed frequency for a bit duration of t seconds. 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. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. When using radio transmitters, it would be impractical to transmit signals in the human voice frequency band directly since, by the theory of electromagnetic waves. In chapter1, we investigated the way of modulating a sinusoidal carrier wave using am technique.
Frequency modulation and phase modulation are the two complementary principal methods of angle modulation. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that. These methods contrast with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency and phase remain constant. Amplitude modulation, modulators, and demodulators ese 488. It is possible to look at the theory of the generation of an amplitude modulated signal in four steps. The carrier wave is generally a sinusoidal waveform characterized by three modifiable parameters, amplitude, frequency and phase, and the corresponding.
In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. 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. Phase modulation is another type of angle modulation very similar to frequency modulation. The extent of amplitude variation in am about a unmodulated carrier amplitude is measured in terms of a factor called modulation index. But phase modulation seems to be in a different categorypm radio is by no means a common term. The basic theory and equations behind amplitude modulation are relatively straightforward and can be handled using straightforward trigonometric calculations and manipulation. It is a modulation system in which the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the signal at the instant of sampling.
The modulation index can be used to make the carrier amplitude more or less sensitive to the variations in the value of the baseband signal. From experiment 3, we know that the amplitude modulation signal utilizes the amplitude of audio signal to modulate high frequency carrier signal. This is accomplished by heterodyning the intelligence frequency with the carrier frequency. Thus completion of the experiment entitled dsbsc generation would be an advantage. Amplitude modulation is used in computer modems, vhf aircraft radio, and in portable twoway radio frequency modulation in this type of modulation, the frequency of the carrier signal varies in accordance with the message signal, and other parameters like amplitude and phase remain constant. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i. Theory of frequency modulation and phase modulation. The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier. It requires that the amplitude of the dc a part of a t is equal to the amplitude of the ac part a. What is amplitude modulation, am electronics notes. Pradeep kshetrapal, tutorials point india private limited. In this video, i have explained amplitude modulation by following outlines.
Frequency modulation is a type of angle modulation. Unicamp university of campinas, state of sao paulo pdf. To extend the range of sound, we need to transmit it through a medium other than air, such as a phone line or radio. Chapter 7 amplitude modulation techniques generation and detection chapter outline 7. Establishing the equation of motion of the vibrating cantilever. What results is a new modulated signal, given by yt cftcos t. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. By the amplitude shift keying theory, we can understand the process of ask technique. Amplitude modulation or am as it is often called, is a form of modulation used for radio transmissions for broadcasting and two way radio communication applications.
The binary signal when ask modulated, gives a zero value for low input while it gives the carrier output for high input. Therefore, when we receive the amplitude modulation signal, we need to restore the audio signal. The purpose of modulation is to transform a message mt. Pulse amplitude modulation pam theory of and its applications. The binary signal when ask modulated, gives a zero value for low input while it. The goal of this experiment is to become familiar with fm modulation and demodulation. This is accomplished by heterodyning the intelligence frequency with. Amplitude modulation theory frequency spectrum power. I ntroduction an amplitude modulated signal is composed of both low frequency and high frequency components. The other type of modulation in continuouswave modulation is the angle modulation. Amplitude modulation a continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information.
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. The simplest method for representing this kind of modulation is fresnels vectorial representation with a consideration of the phase. The carrier frequency, fc, should be larger than the highest spectral component. This type of modulation comes under digital modulation schemes. The amount by which the amplitude of the carrier wave increases and decreases depends on the amplitude of the information signal and is known as modulation index or depth of modulation. An am wave may thus be dscribed, in the most general form, as a function of time as follows. Dutton ee3 winter 2004 1 ee3 lab 1 amplitude modulation and demodulation 1 lab notes a word about power. Overmodulated am signals and its requirement for coherent detection are also considered. Am demodulation amplitude modulation refers to any method of modulating an electromagnetic carrier frequency by varying its amplitude in accordance with the message intelligence that is to be transmitted. Oct 12, 2018 theory of frequency modulation and phase modulation. Amplitudeshift keying ask is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave.
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. 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. Pulse amplitude modulation pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. Amplitude modulation early radio ee 442 spring semester. Pdf theoretical and experimental comparison of amplitude.
Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. The simplest method for representing this kind of modulation is fresnels vectorial representation with. Chapter 7 amplitude modulation techniquesgeneration and. In the frequency domain, amplitude modulation corresponds to translating the baseband spectrum to a band. Amplitude modulation is a very basic form of modulation, and although its simplicity is one of its major advantages, other more sophisticated systems provide a number of advantages. In ask, frequency and phase of the carrier wave is kept constant and only the amplitude is varied according to the digitized modulating signal.
In amplitude modulation the amplitude of high frequency sine wave carrier is varied in accordance with the instantaneous value. Although one of the earliest used forms of modulation it is still used today, mainly for long, medium and short wave broadcasting and for some aeronautical point to point. The general form of a sinusoidal signal can be written as ft. Amplitude shift keying ask is a type of amplitude modulation which represents the binary data in the form of variations in the amplitude of a signal. Channeltochannel variance on signal strength changes on weather and ionosphere conditions.
Pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. In practice, the carrier may be highfrequency hf while the modulation is audio. Amplitude modulation an overview sciencedirect topics. Frequency modulation and phase modulation is a system in which the amplitude of the modulated carrier is kept constant, while its frequency and rate of change are varied by the modulating signal. Amplitude modulation am is a modulation technique used in electronic communication, most. Phase modulation is similar to frequency modulation and is an important technique in digital communication systems. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. Amplitude modulation am, demodulation and their circuit. Angle modulation changes the phase of a signal as well as its amplitude, where amplitude modulation leaves the phase unchanged.
This principle is at the heart of amplitude modulation. Frequency modulation keeps constant the amplitude of the highfrequency oscillation that is used as a signal and to vary the instantaneous frequency for presenting the information. Amplitude modulation is mostly used in the form of electronic communication. When expressed as a percentage it is the same as the depth of modulation. Theory of amplitude modulation afm amplitude modulation. It is specifically designed to stir the interest of junior or senior level electronics minded electrical. A refinement of amplitude modulation, it uses transmitter power and.
In general, amplitude modulation definition is given as a type of modulation where the amplitude of the carrier wave is varied in some proportion with respect to the modulating data or the signal. The focus of this lab is to familiarize the student with the modulation and demodulation of an am signal. Basic concepts of modulation three kinds of modulations modulation is the process of facilitating the transfer of information over a medium. It focuses on the usefulness of numerical simulations. In amplitude modulation, it is the voltage level of the signal to be transmitted. Amplitude modulation or am is a method to transmit signals via electromagnetic transmission. Ask can be considered a digital version of analog amplitude modulation. 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 corresponds to multiplying the carrier by the shifted baseband signal. Amplitude modulation definition, types, solved examples. But we are getting ahead of ourselves, as we have not yet even defined what am is. 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.