Low frequency waves can also occasionally travel long distances by reflecting from the ionosphere (the actual mechanism is one of refraction), although this method, called skywave or "skip" propagation, is not as common as at higher frequencies.
Reflection occurs at the ionospheric E layer or F layers.
Those higher-frequency signals do not follow the surface of the Earth beyond a few kilometers, but can travel as skywaves, ‘bouncing’ off different layers of the ionosphere at different times of day.
These different propagation paths can make the time lag different for every signal received.
All of the profiles have been entered by independent Czech escorts or escort agencies in Prague.
Skywave signals can be detected at distances exceeding 300 kilometres (190 mi) from the transmitting antenna.
Non-directional beacons transmit continuously for the benefit of radio direction finders in marine and aeronautical navigation.
The US Longwave Club of America is interested in "frequencies below the AM broadcast band", Because of their long wavelength, radio waves in this frequency range can diffract over obstacles like mountain ranges and travel beyond the horizon, following the contour of the Earth.
This mode of propagation, called ground wave, is the main mode in the longwave band.