The VLF and LF bauds use _______ propagation for communication.

Answer: Ground (ground/surface wave) propagation

Explanation: VLF and LF signals have very long wavelengths which cause them to travel as surface waves that follow the Earth's curvature and to propagate within the Earth–ionosphere waveguide.

• Frequency ranges: VLF = 3–30 kHz, LF = 30–300 kHz.

• Propagation reason: Long wavelengths diffract and remain guided along the ground, enabling reception beyond the visual horizon.

• Earth–ionosphere waveguide: At these low frequencies the space between the Earth and the ionosphere can guide waves for very long distances, reinforcing ground/surface-wave behaviour.

• Applications: Used for navigation, time/frequency signals, and submarine communications because of deep penetration and long-range stability.

• Why other propagation types are unsuitable: Ionospheric skywave is mainly effective at higher shortwave frequencies; line-of-sight applies to VHF/UHF and above; space/satellite paths are separate systems and not how VLF/LF terrestrial signals propagate.

In summary, VLF and LF use ground/surface-wave propagation (often supported by the Earth–ionosphere waveguide), which allows long-range terrestrial communication beyond the horizon.