Which types of wave propagation are effective in the medium frequency band?

Medium frequency (MF) band propagation is primarily characterized by the dominance of sky and ground waves. Sky waves, which are radio waves that are reflected off the ionosphere, can travel much longer distances, especially at night when ionospheric conditions are more favorable. This enables signals to cover large areas even beyond the horizon. Ground waves, on the other hand, are those that travel along the surface of the Earth, allowing for effective communication over shorter, more local distances.

The combination of these two types of propagation is particularly important in medium frequency applications, such as AM radio broadcasting, as it allows stations to reach both local and distant listeners. This versatility in propagation methods is what makes sky and ground waves the most effective choice in this frequency range.

The other types of wave propagation mentioned—such as surface and subsurface waves—do not significantly contribute to radio communications within the medium frequency band. Direct and reflected waves also do not specifically relate to the primary mechanisms in the MF range. Thus, the effectiveness of both sky and ground waves characterizes the primary radio propagation behaviors utilized in the medium frequency band.