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How is an AM radio signal encoded with voice or music?
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In amplitude modulation (AM), voice or music is encoded onto a radio-frequency carrier wave by varying the wave's amplitude in accordance with the characteristics of the audio signal.12
The process typically follows these steps:
- Conversion: A microphone first converts acoustic sound waves (such as voice or music) into a corresponding electric current. This current fluctuates in a manner that mirrors the original sound pressure variations.3
- Modulation: This electrical information signal is then used to modulate the carrier wave. In AM, the information signal directly varies the amplitude (strength) of the carrier wave.12
- Sideband Creation: This modulation process produces a band of frequencies known as sidebands on either side of the carrier frequency. These sidebands represent the sum and difference between the carrier frequency and the audio information signal.2
Once encoded, the modulated carrier is transmitted and can be recovered by a receiver tuned to the appropriate channel.45