The modulating signal contains the intended message or information sometimes consisting of audio data, as in am radio. Amplitude modulation early radio ee 442 spring semester. Quadratureamplitudemodulationqam dsbsc modulates a signal with bandwidth b to a transmitted signal with bandwidth 2b ssb reduces the transmitted bandwidth to b, but requires more complex modulator reduces snr for a. Note also that the sidebands are separated from the carrier by a frequency equal to that of the tone. Cw modulation is just a multiplication, for montone message and larger carrier. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. The two common forms of analog modulation are amplitude modulation. Its main advantage is that it is more resistant to additive noise than am. Emphasis is placed on explaining the tradeoffs that are made to optimize efficiencies in system design. This principle is at the heart of amplitude modulation. The message signal is, for example, a function of the sound to be reproduced by a. Pulse modulated signals, such as pam, pwm, ppm, pcm and dm. Principles of communication modulation tutorialspoint. The amplitude modulation and frequency modulation are graphically shown in.
In theory an fm signal contains an infinite number of side frequencies so that the band. In the continuouswave modulation, a high frequency sine wave is used as a carrier wave. Introduction modulation is used in efficient radiation of signals. Then inner products dot products are 1 1 0 can interpret inner product as projection of vector 1 v1 onto vector 2 v2in other words, inner product of v1 and v2 tells us how much of vector 1 is there in the direction of vector 2. Amplitude modulation, spectrum of am signal, the balanced modulator, the square law demodulator, dsbsc, ssbsc and vsb, their methods of generation and demodulation, carrier. It is interesting to note that ssb is in fact a low level am modulation system, since it is far.
The envelope contains residue amplitude modulation and therefore varies with time. Next topic pulse code modulation pulsecode modulation pcm is used to digitally represent sampled analog signals. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Polar view of digital iq modulation contd transmission signal is sine wave at frequency f 0 with information encoded in discrete values of amplitude and phase. Changing the amplitude of the carrier am modulation is one type of modulation easy, cheap, lowquality. Angle modulation is the process in which the frequency or the phase of the carrier signal varies according to the message signal.
Modulation is necessary in all of the above scenarios. This is further divided into amplitude and angle modulation. Note that mt has peak amplitude of a m me mma c we note that for ordinary. Amplitude modulation a1 53 experiment aligning the model the low frequency term at to generate a voltage defined by eqn. Introduction to communication system, need for modulation, frequency division multiplexing, amplitude modulation, definition, time domain and frequency domain description. The distortion may be in amplitude, frequency, or phase, depending on the nature of the demodulator. However, more recently with the advent of lowcost microcontrollers and the introduction of domestic mobile telephones and satellite communications, digital modulation has gained in popularity. This form of modulation is essentially derived from two carriers that are 90 out of phase and adding information, either analogue or digital. Quadrature amplitude modulation is widely used for carrying many digital signals, everything from wifi to mobile phone communications and very much more.
Frequency modulation and phase modulation presented a certain immunity to noise, whereas amplitude modulation was simpler to demodulate. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation a continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. If the amplitude of the high frequency carrier wave is varied in accordance with the instantaneous amplitude of the modulating signal, then such a technique is called as amplitude modulation. Amplitude modulation in analog communication tutorial 19. Amplitude modulation is a modulation system in which the carrier wave has its instan taneous. Amplitude modulation in analog communication amplitude modulation in analog communication courses with reference manuals and examples pdf. We considered an example of amplitude modulation in chapter 6 that does this. Security by using coding techniques to avoid jamming. This video presents amplitude modulation in both the time and frequency domains, showing what is happening at each step of the process. So a longer vector has a larger amplitude and hence higher energy.
Overmodulation overmodulation is a condition that occurs when an excessive intelligence signal overdrives an am modulator making %m 100% because e i e c modulated carrier amplitude reach value greater than double of unmodulated value it produces a distortion known as sideband splatter, which results on transmission at frequencies outside. Another way to think is to realize that we are really plotting the amplitude. A typical f c for lowrate telephone line modems is 1800 hz approximate center of 300 3400 band, and for 1200 baud signaling 1200 pulses per. Amplitude modulation refers to the process in which amplitude of the carrier wave is varied with the message signal. Amplitude modulation and frequency modulation duration. Chapter 8 frequency modulationfm fm was invented and commercialized after am. Frequency modulation is the process of varying the frequency of the carrier signal linearly with the message signal. The standard equation of the angle modulated wave is. This is further divided into frequency and phase modulation.
The other type of modulation in continuouswave modulation is angle modulation. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. The amplitude of the analog signal is sampled at uniform intervals and each sample is quantized to its nearest.
We can choose the signal constellation such that the amplitude is the same for all signal alternatives, by placing the signal vectors on a circle in the signal space. That could be the amplitude, phase, or frequency, which result in amplitude modulation am, phase modulation pm, or frequency modulation fm. Spectrum analyzer driverinterface circuit is the modulation level at 50% as calculated from the frequency domain display and is the inband second order product at an acceptable level. Vectors and modulation cse 466 interfacing 3 spose m and n are orthogonal unit vectors. Amplitude and frequencyphase modulation zurich instruments. What is amplitude modulation, am electronics notes. Pradeep kshetrapal, tutorials point india private limited. Most communications systems fall into one of three categories. Chapter 7 multiple division techniques outline frequency division multiple access fdma time division multiple access tdma code division multiple access cdma comparison of fdma, tdma, and cdma walsh codes nearfar problem types of interferences analog and digital signals basic modulation techniques amplitude modulation am frequency modulation fm.
In amplitude modulation, i have covered standard amplitude modulation, dsbsc double sideband suppressed carrier, ssbsc single sideband suppressed carrier, vsb vestigial sideband. Each part may be of any convenient amplitude at the input to an adder. The transmission bandwidth required by dsb sc is b t2b. Amplitude modulation am is a modulation technique where the. Even for the pure tone modulation, the fm spectrum consists of an infinite number. Failure to accurately recover this intelligence will result in distortion and degradation of the demodulated signal and intelligence will be lost.
Amplitude modulation and demodulation abstracta single tone sinusoidal signal is transmitted using amplitude modulation and is demodulated at the receivers end using an envelope detector and the attenuated signal is amplified using common source bjt amplifer i. Lecture notes on analogue communication techniques 1. In a hybrid modulation with the following constellation pattern, the outlying signal sig2, has higher energy i. Instantaneous frequency the instantaneousfrequencyof cos. 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. Pdf analog communication system pdf notes ac notes sw. This application note introduces the concepts of digital modulation used in many communications systems today. For the love of physics walter lewin may 16, 2011 duration. Angle modulation is the process in which the frequency or the phase of the carrier varies according to the message signal. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Note that the commercial radio systems adopted the names of the modulation. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Analog communication angle modulation tutorialspoint.
It is possible to look at the theory of the generation of an amplitude modulated signal in four steps. Both amplitude and phase of ft carry information of ft. Modulating wave, the carrier wave and the modulated waves are graphically shown in the. Communication systems a lecture notes by mahesh lohith k. This part of the lab will demonstrate the use of an ota op amp to provide low level amplitude modulation. It is the standard form of digital audio in computers, cds, digital telephony and other digital audio applications. In modulation, one characteristic of a signal generally a sinusoidal wave known as the carrier is changed based on the information signal that we wish to transmit modulating signal.
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