In amplitude modulation (AM) radio, the complex information such as voices and sounds is carried by modulating the amplitude of a high-frequency carrier wave. The process of modulation involves combining the audio signal (voice or music) with the carrier wave to create a composite waveform. This composite waveform contains the original audio information as variations in the amplitude of the carrier wave.
When the composite waveform is transmitted, it consists of not only the original carrier wave but also additional frequency components called sidebands. These sidebands are created as a result of the modulation process and contain the actual audio information.
The sidebands are positioned symmetrically around the carrier frequency, with one sideband above the carrier frequency and the other below it. The lower sideband (LSB) contains a mirror image of the original audio signal's frequency spectrum, but inverted in phase. The upper sideband (USB) carries the same frequency spectrum as the original audio signal but is not inverted in phase.
To demodulate the received AM signal and extract the original audio information, a process called detection or demodulation is performed. The simplest method of demodulation is envelope detection, which essentially filters out the carrier frequency and extracts the variations in amplitude—the audio signal—from the composite waveform. This process restores the original audio waveform, allowing it to be amplified and reproduced as sound through a speaker.
In summary, the sidebands in AM radio waves carry complex information by modulating the amplitude of a carrier wave with the audio signal. The resulting composite waveform contains the original audio information as variations in amplitude, while the sidebands positioned around the carrier frequency carry the frequency components necessary to reconstruct the audio signal during demodulation.