amplitude modulation

[′am·plə‚tüd ‚maj·ə′lā·shən]

(electronics)

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

(communications)

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

Contrast Frequency Modulation.

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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.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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.