3 and 30 MHz—is a result of skywave propagation. Line of sight propagation pdf at shallow incidence losses remain quite small, signals of only a few w
3 and 30 MHz—is a result of skywave propagation. Line of sight propagation pdf at shallow incidence losses remain quite small, signals of only a few watts can sometimes be received many thousands of miles away as a result. With a single “hop,” path distances up to 3500 km may be reached. Transatlantic connections are mostly obtained with two or three hops.
30 MHz usually penetrate the ionosphere and are not returned to the Earth’s surface. VHF signals including FM broadcast and VHF TV signals are frequently reflected to the Earth during late Spring and early Summer. This leads to an increase in the “skip” or “hop” distance of the skywave at night. Longer distances and higher frequencies using this method meant more signal attenuation. This, and the difficulties of generating and detecting higher frequencies, made discovery of shortwave propagation difficult for commercial services. In 1922 hundreds of North American amateurs were heard in Europe at 200 meters and at least 30 North American amateurs heard amateur signals from Europe.