Which method of radio transmission varies the amplitude of the carrier wave while keeping its frequency constant?

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The technique that varies the amplitude of the carrier wave while maintaining a constant frequency is called amplitude modulation. In amplitude modulation (AM), the strength or amplitude of the carrier signal is changed in proportion to the information signal being sent, such as an audio signal. This allows the signal to carry information, such as music or voice, by changing how 'loud' the radio wave appears at any given time without altering what is known as its frequency.

This method is widely used in AM radio broadcasting, where the transmitted signal can easily be detected and demodulated by receivers. The variations in amplitude correspond to the fluctuations of the audio signal, allowing the receiver to recreate the sound initially captured.

In contrast, frequency modulation (FM) alters the frequency of the carrier wave, while phase modulation affects the phase. Digital modulation involves transmitting data in binary format by manipulating different aspects of the wave, rather than strictly adjusting the amplitude.