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. There are no amplitude scales shown, but you should be able to deduce the depth of modulation 1 by inspection. I ntroduction an amplitude modulated signal is composed of both low frequency and high frequency components. Qam transmitter implementation qam is widely used method for transmitting digital. Learn about the most straightforward way of encoding information in a carrier waveform. Modulation allows us to transmit multiple signals in the same medium i. Amplitude modulation early radio ee 442 spring semester. 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. The basic theory and equations behind amplitude modulation are relatively straightforward and can be handled using straightforward trigonometric calculations and manipulation. In amplitude modulation the amplitude of high frequency sine wave carrier is varied in accordance with the instantaneous value. Amplitude modulation is one of the earliest radio modulation techniques. This principle is at the heart of amplitude modulation.
Ask is sometimes known as onoff keying because the carrier wave swings between 0 and 1 according to the low and high level of input signal respectively theory of amplitude shift keying. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. Therefore, when we receive the amplitude modulation signal, we need to restore the audio signal. The carrier frequency, fc, should be larger than the highest spectral component. Sampling theorem and pulse amplitude modulation pam. The idea is simple, though the notion that it can be used to modulate signals for transmission was hardly obvious before its discovery.
Theory of frequency modulation and phase modulation. The first practical system was put forward in 1936 as an alternative to am in an effort to make radio transmissions more resistant to noise. Before we study in detail about pam lets know the concepts of. The simplest method for representing this kind of modulation is fresnels vectorial representation with. This is also known as ordinary amplitude modulation.
Failure to accurately recover this intelligence will result in distortion and degradation of the demodulated signal and intelligence will be lost. Theory, time domain, frequency domain chapter 4 radio frequency modulation pdf version. Overmodulated am signals and its requirement for coherent detection are also considered. 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, modulators, and demodulators ese. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. Amplitude modulation am is a modulation technique where the amplitude of a highfrequency sine wave. Phase modulation is another type of angle modulation very similar to frequency modulation. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. Dutton ee3 winter 2004 1 ee3 lab 1 amplitude modulation and demodulation 1 lab notes a word about power. Quadrature amplitude modulation qam requires changing the phase and amplitude of a carrier sine wave. The following terms are generally used in regards to amplitude modulation, baseband signal message signal mt carrier signal ct modulated signal st here, amplitude of carrier is changing according to message signal. The extent of amplitude variation in am about a unmodulated carrier amplitude is measured in terms of a factor called modulation index. By the amplitude shift keying theory, we can understand the process of ask technique. Amplitude modulation am, demodulation and their circuit. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. Quadrature amplitude modulation qam national instruments.
The generation of am signals consists simply of the addition of the carrier waveform to the dsb signal, for this reason am 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. This type of modulation comes under digital modulation schemes. The original waveform amplitude is quantized with a resulting loss of information. Theoretical and experimental comparison of amplitude modulation techniques for parametric loudspeakers.
The receivers used to listen to amdsbc are perhaps the simplest receivers of any radio modulation technique. Quadrature amplitude modulation qam is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. The binary signal when ask modulated, gives a zero value for low input while it gives the carrier output for high input the following figure represents ask modulated waveform along with its. Sampling theorem and pulse amplitude modulation pam reference stremler, communication systems, chapter 3. The general form of a sinusoidal signal can be written as ft. Quadrature amplitude modulation qam pam signals occupy. Angle modulation changes the phase of a signal as well as its amplitude, where amplitude modulation leaves the phase unchanged. 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 focus of this lab is to familiarize the student with the modulation and demodulation of an am signal. In this video, i have explained amplitude modulation by following outlines. 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. We have seen that rf modulation is simply the intentional modification of the amplitude, frequency, or phase of a sinusoidal carrier signal. Before we study in detail about pam lets know the concepts of modulation. Keying is indicating the transmission of digital signal over the channel.
Amplitude modulation produces an output signal the bandwidth of which is twice the. Formally, am is defined as a system of modulation in which the amplitude of the carrier is made. It conveys two analog message signals, or two digital bit streams, by changing modulating the amplitudes of two carrier waves, using the amplitudeshift keying ask digital modulation. Types of modulation sine wave carrier described by 3 parameters. Frequency division multiplexing, fdma amplitude modulation and demodulation. Note that this is on the very low end of the recommended voltage range. So can have amplitude modulation am frequency modulation fm phase modulation pm frequency and phase combined are known as angle modulation 8. Amplitude shift keying ask working and applications. Quadrature amplitude modulation qam pam signals occupy twice the bandwidth required for the baseband transmit two pam signals using carriers of the same frequency but in phase and quadrature demodulation. The amplitude of the high frequency carrier of the signal is. When expressed as a percentage it is the same as the depth of modulation. Establishing the equation of motion of the vibrating cantilever. In practice, the carrier may be highfrequency hf while the modulation is audio.
It is specifically designed to stir the interest of junior or senior level electronics minded electrical. From experiment 3, we know that the amplitude modulation signal utilizes the amplitude of audio signal to modulate high frequency carrier signal. Amplitude modulation or am is a method to transmit signals via electromagnetic transmission. 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. One of the easiest ways to implement qam with hardware is to generate and mix two sine waves that are 90 degrees out of phase with one another. The pulse may take any real voltage value that is proportional to the value of the original waveform. Amplitude modulation is mostly used in the form of electronic communication. The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier.
Communication systemsamplitude modulation wikibooks. The demodulation is performed by an envelope detector. 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. A modulating wave, which in theory could be another sine wave, typically at a lower audio frequency is superimposed upon the carrier. Frequency modulation is a type of angle modulation. Formally, am is defined as a system of modulation in which the. 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. Pdf theoretical and experimental comparison of amplitude. Pradeep kshetrapal, tutorials point india private limited. Amplitude modulation theory frequency spectrum power. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information.
Pulse amplitude modulation is the basic form of pulse modulation. Amplitude modulation am is a modulation technique used in electronic communication, most. Amplitude modulation circuit implementation for use in. What we do in am, very roughly,is to throw away the frequency content of. The distortion may be in amplitude, frequency, or phase, depending on. 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. 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. But we are getting ahead of ourselves, as we have not yet even defined what am is. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. The singlesided spectrum of the modulated signal replicates the baseband. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. In this modulation, the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the modulating signal. Unicamp university of campinas, state of sao paulo pdf. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently.
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