Low Frequency and Medium Frequency signals typically travel as what type of waves that follow the Earth's contour?

Low Frequency and Medium Frequency signals typically travel as what type of waves that follow the Earth's contour?

• A. Surface waves that follow the Earth's contour
• B. Sky waves reflected by the ionosphere
• C. Line-of-sight space waves
• D. Ground waves refracted into space

Answer: (A)

Low and medium frequency signals mainly propagate as surface waves, also called ground waves, that travel along and close to the Earth’s surface. Because these long wavelengths interact with the ground, they diffract and hug the boundary between earth and air, allowing the signal to follow the planet’s curvature beyond the horizon. This is why LF/MF transmissions can reach distant locations without needing the ionosphere. In contrast, sky waves rely on ionospheric reflection and are typical of higher frequencies, line-of-sight space waves travel directly through the air without following the surface, and the idea of ground waves refracted into space doesn’t describe the common LF/MF behavior.

Low and medium frequency signals mainly propagate as surface waves, also called ground waves, that travel along and close to the Earth’s surface. Because these long wavelengths interact with the ground, they diffract and hug the boundary between earth and air, allowing the signal to follow the planet’s curvature beyond the horizon. This is why LF/MF transmissions can reach distant locations without needing the ionosphere. In contrast, sky waves rely on ionospheric reflection and are typical of higher frequencies, line-of-sight space waves travel directly through the air without following the surface, and the idea of ground waves refracted into space doesn’t describe the common LF/MF behavior.