What would be the most appropriate HF bands for communicating from San Francisco to Taiwan or the Philippines?

Correct Answer: Option A — 16 or 22 MHz when daylight at each end and 8 MHz when dark at each end.

Trans-Pacific communication over long distances requires higher HF bands (16-22 MHz) during daylight to penetrate the ionosphere and achieve long-range skip. At night, the ionosphere's critical frequency drops significantly, necessitating a shift to lower bands (8 MHz) to ensure the signal reflects back to the Earth's surface.