Ground wave propagation is a mode of radio wave propagation in which radio signals travel along the surface of the Earth, following its curvature. This mode of propagation is primarily associated with low-frequency radio waves, including AM (Amplitude Modulation) and longwave signals. Ground wave propagation is particularly important for local and medium-distance radio communication.
Key characteristics of ground wave propagation include:
- Low Frequencies: Ground wave propagation is most effective at low frequencies, typically below 2 MHz. These frequencies are able to interact with the Earth’s surface and follow its contours.
- Wave Interaction: In ground wave propagation, radio waves interact with the Earth’s surface and are refracted due to changes in the atmospheric properties close to the ground. This refraction allows the radio waves to propagate along the Earth’s surface.
- Limited Distance: Ground wave propagation is effective for relatively short distances, usually up to a few hundred kilometers. As the distance increases, signal strength decreases due to absorption by the Earth and other losses.
- Penetration: Ground waves are capable of penetrating obstacles like buildings, trees, and hills. This makes them suitable for providing coverage in urban areas and over uneven terrain.
- Day-Night Variation: The effectiveness of ground wave propagation can vary based on factors such as time of day and atmospheric conditions. It is often more efficient during the night when the D-layer of the ionosphere, which attenuates ground waves, is less active.
- AM Broadcasting: Ground wave propagation is commonly used for AM broadcasting. AM radio stations typically transmit at frequencies in the medium-wave (MW) range, which is well-suited for ground wave propagation.
- Longwave Communication: Ground wave propagation is also used for longwave radio communication, which can cover larger areas due to its longer wavelengths.
- Low Fading: Ground wave propagation experiences less fading compared to other propagation modes like sky wave (ionospheric) propagation. This contributes to relatively stable signal quality.
- Vulnerability to Obstructions: While ground waves can penetrate obstacles, they are still susceptible to attenuation and distortion if there are significant obstructions or conductive surfaces in the path of the signal.
Ground wave propagation is an important mode of radio wave propagation for local and regional communication, particularly for AM and longwave radio broadcasting. It enables reliable coverage in areas where line-of-sight communication might be obstructed by terrain or buildings.