amplitude modulation

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Related to amplitude modulation: phase modulation, frequency modulation

amplitude modulation:

see modulationmodulation,
in communications, process in which some characteristic of a wave (the carrier wave) is made to vary in accordance with an information-bearing signal wave (the modulating wave); demodulation is the process by which the original signal is recovered from the wave
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; radioradio,
transmission or reception of electromagnetic radiation in the radio frequency range. The term is commonly applied also to the equipment used, especially to the radio receiver.
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Amplitude Modulation


a variation in the amplitude of oscillations (electrical, mechanical, and others) which takes place at a frequency much lower than the frequency of the oscillations themselves. Amplitude modulation is

Figure 1. Harmonic oscillation at a high frequency ω is modulated in amplitude by a harmonic oscillation at a low frequency Ω (τ=1/Ω—itsperiod), t is time, A is the amplitude of the high frequency oscillation, and T is its period.

used in radio technology—for example, in broadcasting. Sound vibrations are converted into electrical oscillations of low frequency Ω (the modulating signal) which periodically vary (modulate) the amplitude of the high frequency oscillations ω (the carrier frequency) generated by a radio transmitter (see Figure 1).

The amplitude-modulated oscillations are radiated in the form of radio waves that are intercepted by radio receivers, where the low frequency modulating oscillations are separated and converted back into an acoustic signal.

amplitude modulation

[′am·plə‚tüd ‚maj·ə′lā·shən]
Abbreviated AM.
Modulation in which the aplitude of a wave is the characteristic varied in accordance with the intelligence to be transmitted.
In telemetry, those systems of modulation in which each component frequency f of the transmitted intelligence produces a pair of sideband frequencies at carrier frequency plus f and carrier minus f.

Amplitude Modulation

(AM) A method of encoding data by varying the amplitude of a constant frequency carrier.

Contrast Frequency Modulation.

amplitude modulation

Varying the voltage of a carrier or a direct current in order to transmit analog or digital data. Amplitude modulation (AM) is the oldest method of transmitting human voice electronically. In an analog telephone conversation, the voice waves on both sides are modulating the voltage of the direct current loop connected to them by the telephone company.

Modulate a Carrier
Amplitude modulation (AM) is also widely used to alter a carrier wave to transmit data. For example, in AM radio, the voltage (amplitude) of a carrier with a fixed center frequency (the station's channel) is varied (modulated) by the analog audio signal.

AM is also used for digital data. In quadrature amplitude modulation (QAM), both amplitude and phase modulation are used to create different binary states for transmission (see QAM). AM is also used to modulate light waves in optical fibers. See modulation and carrier.

Vary the Amplitude
In AM modulation, the voltage (amplitude) of the carrier is varied by the incoming signal. In this example, the modulating wave implies an analog signal.

Digital Amplitude Shift Keying (ASK)
For digital signals, amplitude shift keying (ASK) uses two voltage levels for 0 and 1 as in this example.
References in periodicals archive ?
The change in [U.sub.L] caused by the dynamic change in RL induces an arbitrary amplitude modulation at the PCD antenna.
The VI for amplitude modulation is designed using equation 7 and is presented in Figure 1.
For uncoded amplitude modulation, the binary input sequence is grouped into m bit words and used to select which of the [2.sup.m] modulation symbols (elements of the signal constellation) is to be transmitted during the current modulation interval.
Last year, Martini and his team at Stevens, The Innovation University[TM], developed a method to optically induce fast amplitude modulation in a quantum cascade laser - a process that allows them to control the laser's intensity.
Furthermore, amplitude modulation was a critical contributor to appropriate vibrato.
Focusing more on the physics than the mathematics (though equations are included throughout), McCune begins the volume with discussion of the impact of Shannon capacity and ways its impact can be modulated, an overview of common issues and signal characterization, and individual chapters on digital amplitude modulation, digital frequency modulation, and digital phase modulation.
Salford researchers looked closely at Amplitude Modulation (AM), the conditions which can make turbine noise much worse.
The STV0279E High Performance QAM (Quadrature Amplitude Modulation) Demodulator adds new features to the widely-used STV0279D to deliver dramatic performance improvements that enable the demands on other elements in the reception chain to be relaxed, so reducing Bill of Materials (BOM) costs for manufacturers.
Therefore the resonant precession frequency appears as an amplitude modulation on the light power transmitted through the cesium vapor.
This module is a uni-directional, multi-function device that routes the signal present at the RF input connector through one of its four channels to the RF output connector, for amplitude modulation of the input signal.
The entire suite of audio effects includes: Amplitude Modulation, Chorus, Delay/Echo, Distortion, Dynamics, Compression, Enveloping, Flange/Wah-Wah, Gapper/Snipper, Noise Gate, Pitch Bend/Shift, Reverb, and Vibrato; three Eqs--Graphic, Parametric, and Paragraphic and Time Compression/Expand.
Here, the RF is carried as an amplitude modulation of the optical signals; it is detected at the array elements.

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