What type of propagation allows over-the-horizon VHF and UHF communications to ranges of approximately 300 miles regularly?

Tropospheric ducting is a phenomenon that occurs in the troposphere, the lowest layer of Earth's atmosphere. It involves the bending of radio waves, allowing VHF and UHF signals to travel much further than typical line-of-sight communication would permit. This effect is created when temperature inversions occur or when there are significant differences in humidity and temperature in the atmosphere, which can trap radio waves and direct them over long distances, sometimes reaching up to 300 miles or more.

This mechanism facilitates reliable communication across great distances, particularly useful for amateur radio operators who rely on VHF and UHF frequencies. Tropospheric ducting is relatively common under the right atmospheric conditions and can significantly enhance the coverage area for radio signals.

The other options presented refer to different propagation mechanisms. D region refraction involves lower frequency signals and is primarily associated with nighttime propagation effects. F2 region refraction pertains to high-frequency signals and is significant in the ionosphere but does not typically service VHF and UHF frequencies over such distances. Faraday rotation relates to the rotation of the polarization plane of radio waves due to the Earth's magnetic field and is not a primary mechanism for long-distance communication in the VHF and UHF bands.