Explanation: Low frequency (LF) radio waves primarily propagate via ground wave. This means they travel along the surface of the Earth, following its curvature, making them very stable and reliable for long-distance communication, particularly over conductive surfaces like water. This propagation mode is largely unaffected by ionospheric conditions or solar activity, ensuring continuous and predictable operation. In contrast, High Frequency (HF) relies on skywave propagation (reflection from the ionosphere), which is highly variable and often unreliable for continuous operation due to changing atmospheric conditions and solar activity. Very High Frequency (VHF) and Ultra High Frequency (UHF) signals are mostly line-of-sight, limiting their terrestrial range to relatively short distances and making them unsuitable for general long-distance communication.