Recalls on amplitude modulation am and phase modulation pm are given with. Modulation angular frequency, 2a the modulation amplitude and ji1 is the. We use modulation technique to alter signals in time and frequency to accomplish desired objectives. Digital modulation techniques in digital communication, modulating signal is binary data or an mary encoded version. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. 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. Questions from video lectures of nptel sl no questions video number time in minutes 1 give some examples for the communication systems which use space as the channel. As 16qam transitions to 64qam, 64qam to 256 qam and so forth, higher data rates can be achieved, but at the cost of the noise margin. The message signal is, for example, a function of the sound to be reproduced by a.
Notice that the sine wave will move up and down as the dc is varied, its mean value equalling the dc value. Types of modulation sine wave carrier described by 3 parameters. 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 original waveform amplitude is quantized with a resulting loss of information. The pulse may take any real voltage value that is proportional to the value of the original waveform. This is the simplest form of modulation where the amplitude of the carrier wave is modulated by the analog signal known as.
The amplitude of each of these is constant in value but the resultant wave varies in amplitude in accordance with the audio signal. In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. Set g so that the sinewave peaks just fall to zero. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. Sep 15, 20 lec 10 principles of communication systemsi introduction to amplitude modulation iit kanpur duration. Operation of varying amplitude, frequency or phase of carrier signal accordingly with the instantaneous amplitude of the message signal is called modulation modulation adding information to a carrier signal. 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. The carrier frequency, fc, should be larger than the highest spectral component. Modulation modulation is the process whereby some characteristic of one wave is v aried in accordance with some characteristic of another wave. Modulation can generally be considered to take one of three forms. A percent modulation of greater than 100% is usually to be avoided.
The above mentioned modulation scheme can be re garded as a special case of the amplitude. The idea is simple, though the notion that it can be used to modulate signals for transmission was hardly obvious before its discovery. Modulation presented by nidhi baranwal mca 6th sem 2. Time bit baseband amplitude carrier amplitude process of modulation. The demonstration centers around a number of signals displayed in both the time domain and the frequency domain using a signal generator, an oscilloscope to view the signal. Peak power of psk31 is about 2 times more than average power so a linear amplifier is required 31. Amplitude modulation can be carried out by linearly combining the carrier and intelligence signals then applying the result to a nonlinear component or circuit. Amplitude modulation a1 53 experiment aligning the model the low frequency term at to generate a voltage defined by eqn. 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. 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. Double sideband suppressed carrier dsbsc modualtion consider a sinusoidal carrier ct defined by where ac is the carrier amplitude and fc is the carrier frequency. No information is lost, but the energy is redistributed in the frequency domain. Most radio systems in the 20th century used frequency modulation fm or amplitude modulation am for radio broadcast a modulator is a device that performs modulation. Communication engineering nptel online videos, courses.
The amplitude of the resultant output depends upon the input data whether it should be a zero level or a variation of positive and negative, depending upon the carrier frequency. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. So can have amplitude modulation am frequency modulation fm phase modulation pm frequency and phase combined are known as angle modulation 8. Pdf amplitude and frequency modulation of the small. Another way to think is to realize that we are really plotting the amplitude. We wish to use the carrier wave to carry the message signal, so that the message signal can appropriately be transmitted over a bandpass channel. The efficiency of an am signal with a sinusoidal message signal and. Nptel video lectures, iit video lectures online, nptel youtube lectures, free video lectures, nptel online courses.
The effect of amplitude modulation of pulse trains on the loudness perceived by cochlear implantees was investigated for different overall levels of the signal, modulation depth and the carrier. Each of these is one bit of information, 0s and 1s. This form of modulation is essentially derived from two carriers that are 90 out of phase and adding information, either analogue or digital. In communications, the analog signal shape, by preagreed convention, stands for a certain number of bits and is called a symbol. Amplitude modulation am in which the signal amplitude is varied by the modulating signal while the phase remains unchanged. Digital modulation 1 lecture notes ingmar land and bernard h. Amplitude modulation can be accomplished by multiplying the carrier sine wave by a gain or attenuation factor that varies in accordance with the intelligence signal 2. Introduction to pulse amplitude modulation, spectrum of pam signal and reconstruction, quantization. If the received carrier phase is assumed to be constant, each of the seven reference values will have to be shifted only once at the beginning of the simulation. The am generator, or exciter, as such a low power source of modulated signal is often called, is now set up. In this lecture we will study amplitude modulation and a device which can be used as an amplitude modulator. Unit 8 week 7 signal reconstruction from sampled signal. Pdf amplitude modulation and loudness in cochlear implantees. Using the equation above it can be seen that a modulation index of 0.
Surendra prasad, department of electrical engineering,iit delhi. Weexpresstheresultinganglewe express the resulting anglemodulatedwaveasmodulated wave as 4. Since these side bands are always present in amplitude modulation, the am wave consists of a center frequency, an upper sideband frequency, and a lower sideband frequenmcy. Demonstration with professor sandy hill from the university of massachusetts at amherst. Let ft denote the baseband signal that carries the specification of the message.
So a longer vector has a larger amplitude and hence higher energy. Pdf amplitude and frequency modulation of the small scales. M the modulation amplitude and is the peak change in the rf amplitude from its unmodulated value. Data digital computer output or pcm channel telephone channel, microwave link, etc. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Indian institute of technology kanpur ee 381 electrical. This method is capable of producing nearly 100% modulation with reasonable linearity. This modulates, carrier usually sinusoidal, with fixed frequency.
The basic types of modulation are angular mo dulation including the special cases of phase and frequency modulation and amplitude modulation. Peak power of psk31 is about 2 times more than average power so a linear amplifier is required. As both amplitude and phase are used to carry symbol information, it is very bandwidth efficient. Design and implementation of amplitude modulator and demodulator introduction communication is the most important needs from the very beginning of civilization. Quadrature amplitude modulation is widely used for carrying many digital signals, everything from wifi to mobile phone communications and very much more. Fleury navigation and communications navcom department of electronic systems aalborg university, dk.
Among them, amplitude modulation am is considered the oldest. Rc audio generator, oscilloscope, and spectrum analyzer demonstrations with speech and radio. Unit 4 week3 power efficiency, dsbsc modulation and. Dec 05, 2014 types of modulation sine wave carrier described by 3 parameters. Fleury navigation and communications navcom department of electronic systems. Amplitude modulated signal can be represented by the following equation.
Amplitude modulation let a in the above mentioned signal be. View amplitude modulation research papers on academia. Amplitude modulation can be accomplished by multiplying the carrier sine wave by a gain or attenuation factor that varies in accordance with the intelligence signal. In a hybrid modulation with the following constellation pattern, the outlying signal sig2, has higher energy i. Lecture series on communication engineering by prof. Lec 10 principles of communication systemsi introduction to amplitude modulation iit kanpur duration. This is a carrier symbol that represents one information bit. Many data transmission systems migrate between the different orders of qam, 16qam, 32qam, etc. The amplitude of each of these is constant in value but the resultant wave. Each part may be of any convenient amplitude at the input to an adder. Multiplying the am waveform by the carrier shifts the baseband spectrum down to 0 hz, but it also shifts it up to 2f c in this case 200 mhz, because as stated above multiplication moves the existing spectrum up by f c and down by f c. Farshad lahouti january 20, 2003 winter 2003 uw, ece 318 lecture notes 2 information source signal modulator propagation channel signal demodulator information destination analog communication system analog signals may be transmitted directly via carrier modulat ion over. Sep 15, 20 lecture series on communication engineering by prof.
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