Which frequency range is designated for high-frequency (HF) radio communications?

• A. 1-5 MHz
• B. 3-15 MHz
• C. 3-30 MHz
• D. 30-300 MHz

Answer: (C)

High-frequency communications use the band from three to thirty megahertz. This range is chosen because those frequencies readily reflect off the ionosphere, allowing signals to travel long distances beyond the line of sight—ideal for world-wide or long-range maritime and aviation communications, especially under favorable ionospheric conditions. Frequencies below this range, like one to five megahertz, sit partly in the LF/MF areas and don’t define the full HF band. Frequencies within three to fifteen megahertz are within HF but don’t cover the entire HF range, while frequencies from thirty to three hundred megahertz are in the VHF/UHF regions, which mostly rely on line-of-sight rather than ionospheric reflection. So the designated range for high-frequency communications is three to thirty megahertz.