This type of modulation technique is used in electronic communication. Chapter 6modulation techniques shandong university. Today other forms of modulation are being increasingly used, butamplitude modulation is still in. The first transmission however, was performed by fessenden in 1906 from brant rock, massachusetts. 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. The demodulation is performed by an envelope detector. It is a kind of modulation where the amplitude of the carrier signal is changed in proportion to the message signal while the phase and frequency are kept constant. Examples of digital modulation include qpsk quadrature phase shift keying fsk frequency shift keying msk minimum shift keying qam quadrature amplitude modulation another layer of complexity in many new systems is. Classification and types of analog modulation double sideband suppressed carrierdsb sc introduction. Modulation techniques lmodulation can be done by varying the l amplitude l phase, or l frequency of a high frequency carrier in accordance with the amplitude of the message signal. Other modulation methods amplitude modulation the amplitude of the carrier signal is controlled by the modulating signal pitfall of am. Among them, amplitude modulation am is considered the oldest.
Currently, this technique is used in many areas of communication such as in portable twoway radios, citizens band radio, vhf aircraft radio and in modems for computers. 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. In a hybrid modulation with the following constellation pattern, the outlying signal sig2, has higher energy i. There are three aspects of a signal that can be modulated.
Mary quadrature amplitude modulation mqam is a modulation scheme that conveys data by modulating the data transmission onto the amplitude via two carrier signals. 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. Most radio systems in the 20th century used frequency modulation fm or amplitude modulation am for radio broadcast a modulator is a device. 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. Analog modulation is typically used for am, fm radio, and shortwave broadcasting. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the. This is further divided into amplitude and angle modulation. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. There are no amplitude scales shown, but you should be able to deduce the depth of modulation 1 by inspection. Digital modulation and demodulation fsk,psk,bpsk,qpsk techniques. This can also be extended to frequency modulation fm and frequencyshift keying fsk, for these can be regarded as a special case of phase modulation.
In amplitude modulation or am, the carrier signal has its amplitude. If both the amplitude and the phase are varied proportional to the information signal, quadrature amplitude modulation qam results. So a longer vector has a larger amplitude and hence higher energy. 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. Message information can be transmitted in either the amplitude, frequency, or phase of the carrier, or a combination thereof, in either analog or digital format. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation.
The am radio ranges in between 535 to 1705 khz which is great. We use modulation technique to alter signals in time and frequency to accomplish desired objectives. The two common forms of analog modulation are amplitude modulation. Modulation is the process of converting data into electrical signals optimized for transmission.
In the continuouswave modulation, a high frequency sine wave is used as a carrier wave. Learn the concise history of amplitude modulation or am broadcasting technique. Jun 17, 2018 in this video, i have explained amplitude modulation by following outlines. Digital to analog encoding modulation techniques ask. Amplitude modulation can be carried out by linearly combining the carrier and intelligence signals then applying the result to a nonlinear component or circuit. In amplitude modulation, the of carrier is varied according to the strength of the signal. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. Amplitude modulation, am amplitude modulation was the first type of modulation to be used to broadcast sound. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. Amplitudeshift keying ask frequencyshift keying fsk phaseshift keying psk all of these techniques vary a parameter of a sinusoid to represent the information which we wish to send. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave.
Modulation is the act of changing a signal to transmit useful data. Overmodulation amplitude occurs when signal amplitude is. The threelevel pwm system within this report is created with the possibility of a feedbackregulated system to be implemented in the future. 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. Ee4512 analog and digital communications chapter 3 rectangular pulse amplitude modulation pam svu figure 2. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Linear modulation techniques, including all forms of quadratureamplitude modulation qam and phaseshiftkeying psk, use less bandwidth. In linear modulation the amplitude andor phase of the transmitted signal varies linearly with the digital modulating signal, whereas the transmitted signal amplitude is constant for nonlinear techniques. The threelevel pwm system within this report is created with the possibility of a feedbackregulated system to be implemented in. Amplitude modulation, am, is one of the most straightforward ways of modulating a radio signal or carrier. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. The disadvantages of standard amplitude modulation or dsbfc double sideband full carrier system are as follows.
Amplitude modulation is mostly used in the form of electronic communication. The idea is simple, though the notion that it can be used to modulate signals for transmission was hardly obvious before its discovery. This principle is at the heart of amplitude modulation. Jul 30, 2019 amplitude modulation am frequency modulation fm phase modulation pm amplitude modulation. Advantages and disadvantages of standard amplitude modulation. Not only is the modulation principle used in many forms of scientific instruments and sensors 24, but numerous fields of research also rely on the improved detection sensitivity made available by. Rectangular pulse amplitude modulation pam pages 6064. In this video, i have explained amplitude modulation by following outlines. In fm, the amplitude of the modulating carrier is kept constant while its frequency is varied by the modulating message signal.
It can be achieved in a number of ways, but the simplest uses a single diode rectifier circuit. Overmodulated am signals and its requirement for coherent detection are. Amplitude shift keying ask frequencyshift keying fsk phaseshift keying psk all of these techniques vary a parameter of a sinusoid to represent the information which we wish to send. Phase modulation analog pm and phaseshift keying digital psk can be regarded as a special case of qam, where the amplitude of the transmitted signal is a constant, but its phase varies. Amplitude modulation am is a modulation technique where the amplitude of a highfrequency sine wave. Overmodulated am signals and its requirement for coherent detection are also considered. Most radio systems in the 20th century used frequency modulation fm or amplitude modulation am for radio broadcast. It was the earliest modulation technique used to transmit voice by radio. Analog modulation schemes include amplitude modulation am and frequency. The information is considered as the modulating signal and it is superimposed on the carrier wave by applying both of them to the. The first discovered a method for amplifying very weak signals and basically developed the amplitude modulation technique. Amplitude modulation am and frequencyphase modulation fmpm to new digital modulation techniques. Amplitude modulation was developed in the beginning of the 20th century. The amplitude is the power or intensity of the signal, the frequency is how often the signal repeated itself, and the phase describes where in the cycle the waveform is with respect to time.
The components of each carrier are called inphase and quadrature. The method of varying amplitude of a highfrequency carrier wave in accordance with the information to be transmitted, keeping the frequency and phase of the carrier wave unchanged is called amplitude modulation. We begin our discussion of digital modulation by starting with the three basic types of digital modulation techniques. Quadrature amplitude modulation an overview sciencedirect.
Modulation techniques pwm and pulse code 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. Chapter 7 amplitude modulation techniques generation and detection chapter outline 7. Amplitude modulation is first type of modulation used for transmitting messages for long distances by the mankind. Modulation techniques are roughly divided into four types. This set of data communication and networking multiple choice questions and answers mcqs focuses on digital to analog to encoding modulation techniques amplitudeshift keying ask frequencyshift keying fsk phaseshift keying psk quadrature amplitude modulationqam. Amplitude modulation among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. Amplitude modulation refers to the process in which amplitude of the carrier wave is varied with the message signal. Frequency modulation the frequency of the carrier signal is proportional to the modulating signal phase modulation. Amplitude modulation definition, types, solved examples. Nov 30, 2015 disadvantages of standard amplitude modulation.
As the name implies, this form of modulation involves modulating the amplitude or intensity of the signal. 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. Another way to think is to realize that we are really plotting the amplitude. Chapter 7 amplitude modulation techniquesgeneration and. Principles of communication modulation tutorialspoint. Modulationtypesamplitude,frequency,phase modulation. Other methods of demodulating an am signal use synchronous techniques and provide much lower levels of distortion and improved reception where. Amplitude modulation am frequency modulation fm phase modulation pm amplitude modulation. Analog modulation, digital modulation, pulse modulation, and spread spectrum method. Modulation is the process whereby message information is embedded into the radio frequency carrier. In this modulation, the amplitude of the carrier signal varies in accordance with the message signal, and other factors like phase and frequency remain constant. Ask, fsk, psk, and qam are all forms of digital modulation.
What is amplitude modulation, am electronics notes. Digital modulation in communications systems an introduction. But when compared to frequency modulation, the amplitude modulation is weak, but still it is used for transmitting messages. 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. Aug 28, 2015 amplitude modulation is first type of modulation used for transmitting messages for long distances by the mankind. 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. The modulation technique aims at adapting the frequency band of the useful signal. Quadrature amplitude modulation with amplitude modulation. Pradeep kshetrapal, tutorials point india private limited. Amplitude modulation is one of the oldest forms of modulation in analog communication systems, mostly due to its simplicity of implementation. It conveys two analog message signals, or two digital bit streams, by changing modulating the amplitudes of two carrier waves, using the amplitudeshift keying. A basic amplitudemodulated doublesideband full carrier signal is obtained by mixing a modulating signal y m t at a modulation index m and frequency. These two signals, usually sinusoidal functions such as sine and cosine, are 90 degrees out of phase with each other and are therefore called quadrature carriers.
Pdf a method of contemporary use of digital and analog modulation on the same bandwidth is described. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. Pdf on the combining of the amplitude and phase modulation in. The history of amplitude modulation bright hub engineering. This method is capable of producing nearly 100% modulation with reasonable linearity.
480 1108 1515 655 580 924 1339 618 1566 290 838 1091 419 499 580 444 1217 1352 1309 1102 1110 130 196 1441 126 1333 938 649 454 1427 975 1210 704 588 466 215 1415 1471 1415 712