radio propagation
termnetworking
How a radio signal actually travels from transmitter to receiver, which depends far more on frequency than on power.
Three modes explain nearly everything. Ground wave follows the earth's surface and dominates below about 2 MHz. Sky wave, between roughly 2 and 30 MHz, is refracted by the ionosphere back to earth and can cross oceans in multiple hops. Line of sight takes over above about 30 MHz. The ionosphere varies by day and night, season, and the eleven-year solar cycle, which is why an HF path that worked this morning can be dead this afternoon.
Also known as: ground wave, sky wave, line of sight, ionosphere