Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. Or the process of modulation can be defined as varying the rf carrier wave in accordance with the intelligence or information in a low frequency signal. Techniques for modulating uwb pulses include pulse position modulation and pulse amplitude modulation. Amplitude modulation definition and meaning collins. Am signals can be received by a crystalpowered radio set, that. When expressed as a percentage it is the same as the depth of modulation. The amplitude or peak amplitude of a wave is a measure of how big its oscillation is amplitudes are always measured as positive numbers for example. It is simple to demodulate and this means that radio receivers capable of. 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. The signal can travel long distances, and appear in faraway places, because of the earths ionosphere. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Definition of amplitude modulation in the dictionary.
Carrier modulation allows the transmission of modulating frequencies without the use of transmission wire as a medium. For example, the signal in a cell phone is a voice signal with a. 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. An interactive demo which enables you to both see and hear the result of multiplying a sine wave with a cosine amplitude envelope. Amplitude modulation is performed simply by adding mt to c. The more common approach of ppm, for instance, might assign a digital representation of 0 or 1 to the transmitted and received pulse based on where, in time, the pulse is placed. The resulting signal from the process of amplitudemodulation is called amplitude modulation signal of simply am wave. Commercial am stations operate at frequencies spaced 10 khz. As we mentioned before, well use dsbc modulation because of its ease in demodulation. Frequency modulation frequency modulation is a change in the carrier frequency fc with all other factors remaining constant. Amplitude modulation is an increase or decrease of the carrier voltage ec, will all other factors remaining constant. Modulation is the process of superimposing a low frequency signal on a high frequency carrier signal.
For am, it relates to the variations in the carrier amplitude and is defined as so if h 0. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. 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 amplitude modulation am, auditory or visual information is impressed on a carrier wave by varying the amplitude of the carrier to match the fluctuations in the audio or video signal being transmitted. Instead of modulating the amplitude of the first waveform, were going to modulate its frequency. Amplitude modulation wikipedia, the free encyclopedia. Amplitudemodulation article about amplitudemodulation. As for the mechanism, when amplitude modulation is used there is a variation in the amplitude of the carrier. As with other modulation indices, in am, this quantity, also called modulation depth, indicates by how much the modulated variable varies around its original level. Amplitude modulation am is a process by which the wave signal is transmitted by modulating the amplitude of the signal.
Phase modulation phase modulation is a change in the carrier phase angle. Amplitude modulation, am is being used less in its basic format, but it provides the. Modulation definition need for modulation types of. However its presence provides a simple means of demodulation using envelope detection, providing a. Am is the oldest method of broadcasting radio programs. The equation for the simple sine wave of frequency. Amplitudemodulation article about amplitudemodulation by. Amplitude modulation is a technique by which the amplitude of the carrier wave is changed according to the signal wave or modulating signal. A disadvantage of all amplitude modulation techniques, not only standard am, is that the receiver amplifies and detects. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Overmodulated am signals and its requirement for coherent detection are also considered. Modulation in which the amplitude of a carrier wave is varied in accordance with some characteristic of the modulating signal. Message signal embed into the amplitude of carrier simple am is also called.
Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. The instantaneous amplitude overall signal power varies depending on the instantaneous amplitude of the modulating data. For example, when using acoustic signals, the radiating element is the loudspeaker the physical dimensions of which depend on the frequency band and on the. Amplitude modulation, usually shortened to am, is a simple way to send a radio signal. 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. Amplitude modulation was the earliest modulation technique used to transmit voice signals by radio signals. Over an individual pulse there occurs an oscillating frequency modulation with amplitude of 1 2 khz fig. The block diagram that describes this is deceptively simple, as i have shown in figure 2. Demonstration with professor sandy hill from the university of massachusetts at amherst. Double sideband large carrier dsblc modultion for general message signal mt. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process.
Amplitude simple english wikipedia, the free encyclopedia. Amplitudes are always measured as positive numbers for example. Amplitude modulation or am is a method to transmit signals via electromagnetic transmission. Amplitude modulation implies the modulation of a coherent carrier wave by mixing it in a nonlinear device with the modulating signal to produce discrete upper and lower sidebands, which are the sum and difference frequencies of the. Amplitude modulation definition of amplitude modulation by. Or modulation is defined as the precess by which some characteristics, usually amplitude, frequency or phase, of a carrier is varied in. In early am transmitters the amplitude modulator circuit was a key element of the transmitter. That could be the amplitude, phase, or frequency, which result in amplitude modulation am, phase modulation pm, or frequency modulation fm. Amplitude modulation, am, is one of the most straightforward ways of.
The binary signal when ask modulated, gives a zero value for low input while it gives the carrier output for high input the following figure represents ask modulated waveform along with its. Amplitude modulation article about amplitude modulation. Amplitude modulation am is a method of impressing data onto an alternatingcurrent ac carrier waveform. In the process of amplitude modulation, the frequency and phase of the carrier remain constant whereas the maximum amplitude varies according to the instantaneous value of the information signal. Peak value of carrier signal can also be computed using the peaktopeak value of the am waveform see fig.
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 amplitude modulation am modulation index can be defined as the ratio of the peak value of the message signal to the amplitude. Amplitude modulation definition of amplitude modulation at. The signal can travel long distances, and appear in faraway places, because of the earths ionosphere amplitude is the height of a wave. Source called v1 generates the message to be transmitted.
Amplitude modulation definition is modulation of the amplitude of a radio carrier wave in accordance with the strength of the audio or other signal. 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. 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. Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave.
Frequency modulation definition of frequency modulation by. Amplitude modulation am, demodulation and their circuit. Pulse amplitude modulation pam theory of and its applications. The carrier frequency, fc, should be larger than the highest spectral component. The main advantage is that since a coherent reference is not required for demodulation as long as 0 simple and inexpensive.
Amplitude modulation a1 53 experiment aligning the model the low frequency term at to generate a voltage defined by eqn. Amplitude modulation simple english wikipedia, the free. A method of transmitting signals, such as sound or digital information, in which the value of the signal is given by the amplitude of a. Amplitude modulation early radio ee 442 spring semester. Frequency modulation definition of frequency modulation. The technical way to describe the am process involves an initial oscillator called the carrier, which is what gets heard in the traditional way, while the second. This method is capable of producing nearly 100% modulation with reasonable linearity. Am is still widely used for broadcasting on the long, medium and short wave bands. Amplitude modulation definition, types, solved examples. Quadrature amplitude modulation is widely used for carrying many digital signals, everything from wifi to mobile phone communications and very much more. The concluding part will be spent looking at the more popular form of high level modulation known as collector modulation or heising, named after its inventor.
Each part may be of any convenient amplitude at the input to an adder. Amplitude modulation is still used in many forms of communication. The binary signal when ask modulated, gives a zero value for low input while it gives the carrier output for high input. It is a type of pulse time modulation ptm technique where the timing of the carrier pulse is varied according to the modulating signal in pulse duration modulation pdm, the amplitude of the pulse is kept constant and only the variation in width is noticed. Amplitude modulation synthesis is a counterintuitive method of creating harmonic content. Continue reading to learn about amplitude modulation in the modular domain. Amplitude modulation may be defined as a system in which the maximum amplitude of the carrier wave is proportional to the instantaneous value amplitude of the modulating or base band signal. A carrier wave is modulated changed by adding audio. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. Amplitude modulation definition and meaning collins english.
Before we study in detail about pam lets know the concepts of modulation. Am is defined as a process in which the amplitude of the carrier. Information and translations of amplitude modulation in the most comprehensive dictionary definitions resource on the web. Before we study in detail about pam lets know the concepts of. Amplitude modulation is a modulation method in which the carrier amplitude changes with the input signal amplitude. Thats because distance can only be greater than zero or. Amplitude modulation article about amplitude modulation by. In this modulation, the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the modulating signal. A method of transmitting signals, such as sound or digital information, in which the value of the signal is given by the amplitude of a high frequency carrier wave. Transmitters that transmit amplitude modulated signals require an am modulator circuit to produce the required signal.
Rc audio generator, oscilloscope, and spectrum analyzer demonstrations with speech and radio. The highest frequency of the modulating data is normally less than 10 percent of the carrier frequency. The number of possible pulse amplitudes can be infinite in the case of analog pam, but it is usually some power of two so that the. Amplitude modulation is used in a variety of applications. According to the standard definition, the amplitude of the carrier signal varies in accordance with the instantaneous amplitude of the modulating signal. When the peaktopeak amplitude of the modulationg signal is equal to the peaktopeak amplitude of. Pulse amplitude modulation is the basic form of pulse modulation. Pulse amplitude modulation pam is the transmission of data by varying the amplitude s voltage or power levels of the individual pulses in a regularly timed sequence of electrical or electromagnetic pulses. The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier. The demodulation is performed by an envelope detector. 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 modulation definition of amplitude modulation. An introduction to frequency modulation sound on sound.
The amplitude or peak amplitude of a wave is a measure of how big its oscillation is. Amplitude modulation definition, types, solved examples byjus. This form of modulation is essentially derived from two carriers that are 90 out of phase and adding information, either analogue or digital. There are many ways in which amplitude modulation can be generated and a variety of circuits that can be used. When the peaktopeak amplitude of the modulationg signal is equal to the peaktopeak amplitude of the unmodulated carrier, amplitude modulation. Thats because distance can only be greater than zero or equal to zero. The measurement and definition of amplitude modulations. 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. Here is the circuit used for modulation and its simulation. Percentage modulation aka modulation index or modulation factor measure of extend to which carrier voltage is varied by intelligence defined as. Among various modulation schemes, amplitude modulation is the simplest and oldest modulation technique. Similarly, the equation describing frequency modulation equation 4 looks no more fearsome than that describing amplitude modulation. This principle is at the heart of amplitude modulation. What we do in am, very roughly,is to throw away the frequency content of.
1478 559 506 778 127 1194 533 38 548 1330 223 1475 1009 750 714 1114 1302 282 977 120 342 851 66 280 533 967 1252 1281 629 128 642 67 470 34 623 1447 236 800 957 1446