Which are long-range OTH systems?

• A. HF and Satellite Communication (SATCOM)
• B. VHF and UHF
• C. HF only
• D. SATCOM only

Answer: (A)

Long-range OTH systems extend communication beyond the line of sight by using methods that bypass the curvature of the Earth. High Frequency signals travel as skywave, being reflected by the ionosphere back to distant receivers, enabling long-distance links that can span continents or oceans—though their reliability varies with time of day and solar activity. Satellite communications relay signals through orbiting satellites, providing broad global coverage regardless of terrain, which is another form of long-range reach.

Thus, combining HF skywave capability with SATCOM’s satellite relay covers long-range OTH communication in complementary ways: HF reaches far across the globe when conditions allow, while SATCOM provides widespread, near-global reach through space-based relays. VHF/UHF are typically confined to line-of-sight ranges and don’t offer the same horizon-skipping capability, and HF alone doesn’t incorporate the satellite path that extends reach even further.