The basic form of any process, that repeats itself periodically, is a pure sine wave of constant amplitude and frequency. Processes of a complicated nature, with amplitude or frequency changing in a haphazard manner, are composed of several elementary sinusoidal oscillations. If a 20 kHz wave is amplitude modulated with a 4 kHz wave, there exist in reality three oscillations having constant amplitude: a stronger oscillation of 20 kHz, and two equally weak oscillations of (20 – 4) = 16 kHz, and (20 + 4) = 24 kHz. The three of them appear one above the other. Adding together the amplitudes of the three waves, point by point, results in the amplitude modulated wave, Fig. 30.18.

Amplitude modulation does not signify the alteration ...

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