The frequency of the modulation signal determines the rate of the frequency change from the center frequency. Figure 1 shows four different waveforms corresponding to the above equation with varying values of m. Ssb generator and the am dsb receiver, as well as terminology used in amplitude modulation. In this discussion, we focus on amplitude modulation only. Quadrature amplitude modulation qam is a modulation scheme that moderates two sinusoidal carriers 90 outofphase with each other. Pulse amplitude modulation pam theory of and its applications. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. Here frequency of rf carrier is varied in accordance with frequency of modulating signal input. Amplitude modulation circuit implementation for use in. What this means that we only modulate that is increasing or decreasing the amplitude of the wave to be transmitted as a signal so as to not affect its content but. Amplitude modulation can be produced in various ways. Amplitude modulation an overview sciencedirect topics. Modulation allows us to transmit multiple signals in the same medium i. Since the frequency change of a sinusoid in time results in alternation of phase in time, fm may also be referred to as phase modulation, or pm, as well.
In this modulation, the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the modulating signal. Here amplitude of rf carrier is varied in accordance with amplitude of modulating signal input. The modulating signal contains the intended message or information sometimes consisting of audio data, as in am radio. Modulation is a technique by which we can transfer our information at a distance. We also see how to use a balanced mixer to modulate a signal. Amplitude modulation am is a modulation technique where the. It is still in use today in a variety of systems, including, of course, am broadcast radio. In particular, we discuss amplitude and frequency modulation. We are only going to discuss the ring modulator because it is the. This lab gives you the opportunity to actually work on amplitude modulation and reinforce the theory taught in class. Collector modulation method is the example of high level amplitude modulation.
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. The effect of amplitude modulation index and frequency modulation index on total harmonic distortion in 1phase inverter to cite this article. Binary phase shift keying digital modulation technique for. Dutton ee3 winter 2004 1 ee3 lab 1 amplitude modulation and demodulation 1 lab notes a word about power. The amplitude of the fm signal is constant at all times and is independent of the modulation signal. Amplitude modulation and demodulation objective amplitude modulation am is one of the simplest methods for modulating a sinusoidal carrier wave.
Frequency division multiplexing, fdma amplitude modulation and demodulation. The amplitude of the modulation signal determines the amount of the frequency change from the center frequency. 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. Course projects are one of the seven high impact practices discussed by koh in 1. The purpose of this lab is for you to gain familiarity with the concepts of amplitude modulation and demodulation. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. A brief discussion about pulse code modulation and demodulation. Complex exponential and sinusoidal amplitude modulation. Jun 03, 2016 this paper focuses on the binary phase shift keying digital modulation technique for noiseless and noisy transmission with the following objectives. Overmodulated am signals and its requirement for coherent detection are also considered. Pulse amplitude modulation an overview sciencedirect topics.
Modulation is defined as a process in which the amplitude of the carrier wave ct is varied linearly with the instantaneous amplitude of the message signal mt. As we will see, modulation techniques not only allow us to. This gives us something to modulate and carry the information pattern from. This electrical signal is called the message or baseband signal. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Amplitude modulation am is similar to dsb but has the advantage of permitting a simpler demodulator, the envelope detector. Am and fm both are used as analog modulation techniques.
Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. Introduction the process of changing some characteristic e. In amplitude modulation, it is the voltage level of the signal to be transmitted. We can also get back our analog signal by demodulation. In chapter 6, we will discuss am and other modulation systems and will illustrate them with matlab. The second is to investigate classical analog amplitude modulation and the envelope detector. What is amplitude modulation, am electronics notes. Amplitude modulation early radio ee 442 spring semester. The transmission of a wave signal by modulating the amplitude of the signal is amplitude modulation. Science only amplitude phase and frequency of the wave can be changed so we have three basic type of modulation 1. This makes the problem of am more difficult to identify and it can often be missed by those investigating noise complaints if residents descriptions of the noise do not match those that the investigator considers relate to am. Amplitude modulation part 1 in class you have studied the theory of amplitude modulation.
Pcm is in binary form,so there will be only two possible states high and low 0 and 1. A type of dsb, called binary phaseshift keying, is used for digital telemetry. Double sideband dsb is one of the easiest modulation techniques to understand, so it is a good starting point for the study of modulation. Here well use the example of a square law fet as illustrated in figure 9. However, this conclusion leaves the possiblity that dis tortions which are insigni. The message signal is then used to electrically vary the amplitude. Wideband interference in the vicinity of 38753900 kcs. In high level amplitude modulation system, modulation is done at high power of carrier and modulating signals so power amplifiers are used to boost the carrier and modulating signals before modulation.
Amplitude modulation discussion document 3 wind farm noise and am can be described in a variety of ways. To study amplitude demodulation by linear diode detector 3. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. 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. The components of each carrier are called inphase and quadrature. The resulting amplitude modulation am waveform is then demodulated.
To study frequency modulation and determine its modulation factor 4. This form of modulation is essentially derived from two carriers that are 90 out of phase and adding information, either analogue or digital. An am wave may thus be dscribed, in the most general form, as a function of time. Experiment 5 amplitude modulation preliminary discussion in an amplitude modulation am communications system, speech and music are converted into an electrical signal using a device such as a microphone. Before we study in detail about pam lets know the concepts of modulation. There are no amplitude scales shown, but you should be able to deduce the depth of modulation 1 by inspection. 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. Both modulated carriers are summed to result in a signal with amplitude and phase modulation. Quadrature amplitude modulation is widely used for carrying many digital signals, everything from wifi to mobile phone communications and very much more. If this minimum value is zero, the modulation depth is 100%. Note that this is on the very low end of the recommended voltage range.
The demodulation is performed by an envelope detector. It requires that the amplitude of the dc a part of a t is equal to the amplitude of the ac part a. Pulse code modulation is a method that is used to convert an analog signal into a digital signal, so that modified analog signal can be transmitted through the digital communication network. Yet, am continues to be used today in many communication applications. This principle is at the heart of amplitude modulation. Pulse amplitude modulation is the basic form of pulse modulation. To study sampling and reconstruction of pulse amplitude modulation system 6. The standard form of an amplitude modulated am wave is defined by. Although modulation index is related to percentage of modulation as discussed below, section 73. Amplitude modulated signal can be represented by the following equation. The autocorrelation of a stationary random process, which was discussed. More complete discussions of am and analog implementa tions can be. Amplitude modulation is a modulation system in which the carrier wave has its.
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