Propagation
Because of their long wavelength, low frequency radio waves can diffract over obstacles like mountain ranges and follow the curvature of the Earth. This mode of propagation, called ground wave, is the main mode in the LF band. The attenuation of signal strength with distance by absorption in the ground is lower than at higher frequencies. Low frequency ground waves can be received up to 2000 km from the transmitting antenna.
Low frequency waves can also travel long distances by reflecting from the ionosphere (the actual mechanism is one of refraction), although this method, called skywave or "skip" propagation, is not as common as at higher frequencies. Reflection occurs at the E layer or F layers. Skywave signals can be detected at distances exceeding 300 km from the transmitting antenna.
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