Information is transmitted over radio waves using a process called modulation. Modulation involves modifying one or more properties of the radio wave, such as its amplitude, frequency, or phase, in order to encode the desired information.
There are several modulation techniques used in radio communication, but the two most common ones are amplitude modulation (AM) and frequency modulation (FM).
Amplitude Modulation (AM): In AM, the amplitude of the radio wave is varied in proportion to the audio signal that carries the information. The audio signal could be, for example, the sound of a voice or music. The carrier wave, which is a high-frequency wave, is typically much higher in frequency than the audio signal. By varying the amplitude of the carrier wave according to the audio signal, the information is embedded in the modulated wave. This modulated wave can then be transmitted over the air.
Frequency Modulation (FM): In FM, the frequency of the carrier wave is varied in proportion to the audio signal. As with AM, the audio signal represents the information to be transmitted. When the audio signal has higher amplitude, the frequency of the carrier wave increases, and when the audio signal has lower amplitude, the frequency decreases. The changes in frequency are continuous and smooth, resulting in a modulated wave that carries the information.
In both AM and FM modulation, the modulated wave is transmitted through an antenna, which converts the electrical signals into electromagnetic waves that propagate through the air as radio waves. These radio waves can be received by another antenna, which then demodulates the wave, extracting the original information from the modulation.
It's worth noting that there are other modulation techniques used in different contexts, such as phase modulation (PM) and quadrature amplitude modulation (QAM), which are commonly used in digital communication systems. However, the fundamental principle of encoding information onto radio waves through modulation remains the same.