Refraction is a phenomenon that occurs when an FM radio signal passes through a medium with a varying refractive index, such as the Earth’s atmosphere. Refraction causes the signal to change direction, and this change can affect the signal’s strength and quality.
As FM radio signals travel through the atmosphere, they encounter various layers of air with different temperatures and densities, which can cause the signal to refract or bend. This bending can cause the signal to travel farther than it would if the atmosphere were uniform, but it can also cause interference and fading.
In particular, a phenomenon called ducting can occur when a layer of warm air traps a layer of cool air near the surface of the Earth. This duct can act like a waveguide, causing FM radio signals to travel farther and more efficiently than they would through normal atmospheric conditions. However, ducting can also cause interference and distortion, as the signal may bounce around inside the duct and interfere with itself.
FM radio transmitters take these atmospheric effects into account when transmitting signals. They may adjust the frequency or power of the signal to compensate for refraction and other atmospheric effects, ensuring that the signal maintains its quality and consistency over long distances.