Scribd is the worlds largest social reading and publishing site. In this case, since the source is a multimedia file rather than a pure sine wave, we need the dsp process, which is the resampling and filtering. Build simple am modulator by using crystal oscillator. Amplitude modulation contents slide 1 doublesideband suppressedcarrier amplitude modulation slide 2 spectrum of a dsbscam signal slide 3 why called doublesideband slide 4 ideal coherent receiver slide 5 coherent receiver analysis slide 6 spectra in dsbscam system slide 7 demodulator using the preenvelope slide 8 costas loop demodulator.
Hi, im a beginner in matlab and im just wondering whether the modulation constant. The distortion may be in amplitude, frequency, or phase, depending on the nature of the demodulator. Ssb modulation by dsbscam and filtering in singlesidebandssb modulation only the. Once a signal has been modulated, information is retrieved through a demodulation process. We will add additional functions to build the am demodulator. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Chapter 7 singlesidebandmodulationssb andfrequency. Amplitude modulation and demodulation electrical and computer.
Overmodulated am signals and its requirement for coherent detection are also considered. The demod ulation is performed by an envelope detector. Am modulation and demodulation part 1 this video uses properties of the fourier transform to explain modulation and demodulation inside a simple am radio. Use your project files from the previous fir laboratory.
There are no amplitude scales shown, but you should be able to deduce the depth. What we do in am, very roughly,is to throw away the frequency content of. To study amplitude demodulation by linear diode detector 3. This is the modulation where the phase of the carrier signal is altered according to the low frequency of the message signal is called phase modulation. This experiment examines the characteristics of the amplitude modulation am process. When expressed as a percentage it is the same as the depth of modulation. Implementation of binary ask modulation and demodulation using matlab considering fixed information. Chapter 6 doublesideband suppressedcarrier amplitude. In frequency modulation, the amplitude of the carrier. An amplitude modulated signal is composed of both low frequency and high.
Amplitude modulation am, demodulation and their circuit. Department of electronics and communication engineering. Note that this is on the very low end of the recommended voltage range. In amplitude modulation the amplitude of high frequency sine wave carrier is varied in accordance with the instantaneous value of the modulating. These sample pulses can be transmitted directly using wired media or we can use a carrier signal for transmitting through wireless. To generate amplitude modulated wave and determine the percentage modulation. Amplitude modulation early radio ee 442 spring semester. Qam is composed of two independent pulse amplitude modulation pam baseband modulations placed on the quadrature rails. To demodulate the modulated wave using envelope detector. To study frequency modulation and determine its modulation factor 4. Doublesideband suppressedcarrier transmission dsbsc is transmission in which frequencies produced by amplitude modulation am are symmetrically spaced above and below the carrier frequency and the carrier level is reduced to the lowest.
Pulse amplitude modulation is the basic form of pulse modulation in which the signal is sampled at regular and each sample is made proportional to the amplitude of the modulating signal at the sampling instant. Is there a way i can vary it, say, to 100% modulation depth. To study sampling and reconstruction of pulse amplitude modulation system 6. This principle is at the heart of amplitude modulation. Laboratory manual principles of communication system lab ee226f ivth semester. In practice, the carrier may be highfrequency hf while the modulation is audio. The idea is simple, though the notion that it can be used to modulate signals. Failure to accurately recover this intelligence will result in distortion and degradation of the demodulated signal and intelligence will be lost. This is the same as the am modulation above but without the carrier. To study and perform pulse amplitude modulation and demodulation. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. In this code, it is considered the default value of ma equal to 1 for hundred percent modulation.
Both phase and frequency of carrier are known at the demodulator amplitude of. Doublesideband suppressedcarrier transmission wikipedia. Bookmark file pdf amplitude modulation tutorial solutions funda in this video, i have explained am examples on multi tone am signals by following outlines. Matlab code for amplitude modulation am file exchange. The amplitude modulation schemes like am,dsbsc and ssbsc systems can not handle inherent nonlinearities in a really good manner where as fm can handle it very well. Explain generation and demodulation of pam, ppm and pwm with waveforms. Pulse width modulation is a modulation process or technique used in most communication systems for encoding the amplitude of a signal right into a pulse width or duration of another signal carrier signal for transmission. Slide 8 transforms in generating ssb signal slide 9 coherent ssb demodulation slide 10 coherent demodulation cont.
Each channel sharing scheme a set of basis vectors. Explain generation and demodulation of pam, ppm and pwm. Modulation and demodulation this chapter describes the essential principles behind modulation and demodulation, which. This document is highly rated by computer science engineering cse students and has been viewed 1115 times. If not, what is the default depth of modulation for am here. Keying is indicating the transmission of digital signal over the channel. The modulated signal y has zero initial phase and zero carrier amplitude, resulting from a suppressedcarrier modulation. Amplitude modulation theory frequency spectrum power. Analog modulation and demodulation amplitude modulation pages 306309. In the pulse amplitude modulation, the message signal is sampled at regular periodic or time intervals and this each sample is made proportional to the magnitude of the message signal. To study and perform frequency modulation and demodulation. In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors. This type of modulation comes under digital modulation schemes. In the context of radio communication, near the end of the 2oth century, few modulated signals contain a significant component at carrier frequency.
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. Vsb signals are generated using standard am or dsbsc modulation, then passing modulated signal through a sideband shaping. There are two reasons why frequencydivision multiplexing works. In fact, all radio channels in the am band use this type of modulation. Ee4512 analog and digital communications chapter 6 the analytical signal for double sideband, large carrier amplitude modulation dsblc am is. If the baseband signal is bandlimited, then there is a. The amplitude of the high frequency carrier of the signal is. 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. Amplitude modulation am is an analog modulation scheme where the amplitude a of. Chapter 5 amplitude modulation am, ppt, adc, semester. The main advantage of this form of am demodulator is that it is very simple and cheap. Matlab code for ask modulation and demodulation file. 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. 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.
Building simulink model of the music transmission using dsbam modulator and demodulator baseband here, we will implement the dsbam baseband modulator and demodulator using a music file as a source. The process and the signal were called amplitude modulation, or am for short. If we were to implement every possible combination of demodulation algorithm, carrierrecovery technique, and clock regeneration as a distinct model, the combinatorial explosion of different models would become unmanageable. Demodulation uses either standard am or dsbsc demodulation, depending on whether a carrier tone is transmitted. The focus of this lab is to familiarize the student with the modulation and demodulation of an am signal. The radio wave was called a carrier, since it was seen to carry the speech information with it. The carrier signal and y have sampling frequency fs. The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier. Amplitude modulation or am is a method to transmit signals via electromagnetic transmission. Slide 24 theory of the pilot tone filters slide 25 tone filter theory cont. To study and perform amplitude modulation and demodulation. Types of amplitude modulation am double sideband with carrier we will call it am. I ntroduction an amplitude modulated signal is composed of both low frequency and high frequency components. Amplitude modulation is one of the oldest forms of modulation.
Amplitude modulation definition, types, solved examples. Amplitude modulation and demodulation 1 lab notes a word about power. Fm is a system in which the amplitude of the carrier wave ct is kept. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Radio waves can carry audio, video, and digital information over great distances by using changes in a carrier waves amplitude, frequency, or phase to represent the information being transmitted. As for the mechanism, when amplitude modulation is used there is a variation in the amplitude. Vsb modulation with envelope detection is used to modulate image in analog tv signals. The spectral efficiency of the transmitted ask waveform is also a consideration and the m. Introduction to modulation and demodulation modulation. It is actually used for controlling the amplitude of digital signals in order to control devices and applications. Any baseband signal can be broken up into a weighted sum of sinusoids using fourier decomposition chapter.
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