Shortwave Propagation

"Shortwave radio" refers to radio transmission over the shortwave bands (SW) at radio frequencies. There is no official definition of the band range, but it always includes all of the high frequency band (HF), which extends from 3 to 30 MHz (100 to 10 meters); above the medium frequency band (MF), to the bottom of the VHF band.

The ionosphere refracts radio waves in shortwave bands, allowing them to be "bounced" back to Earth at great distances through skywave or "skip" propagation.

Thus shortwave radio can be used for communication over very long distances, in contrast to radio waves of higher frequency, which travel in straight lines (line-of-sight propagation) and are limited by the visual horizon, about 60 km.

Amateur radio operators discovered that long-distance communication was possible on shortwave bands.

The project "Understanding HF Propagation" focuses on near-real-time indicators and explains what they mean.