<Ul> <Li> Indirect propagation: Radio waves can reach points beyond the line - of - sight by diffraction and reflection . Diffraction allows a radio wave to bend around obstructions such as a building edge, a vehicle, or a turn in a hall . Radio waves also reflect from surfaces such as walls, floors, ceilings, vehicles and the ground . These propagation methods occur in short range radio communication systems such as cell phones, cordless phones, walkie - talkies, and wireless networks . A drawback of this mode is multipath propagation, in which radio waves travel from the transmitting to the receiving antenna via multiple paths . The waves interfere, often causing fading and other reception problems . </Li> </Ul> <Li> Indirect propagation: Radio waves can reach points beyond the line - of - sight by diffraction and reflection . Diffraction allows a radio wave to bend around obstructions such as a building edge, a vehicle, or a turn in a hall . Radio waves also reflect from surfaces such as walls, floors, ceilings, vehicles and the ground . These propagation methods occur in short range radio communication systems such as cell phones, cordless phones, walkie - talkies, and wireless networks . A drawback of this mode is multipath propagation, in which radio waves travel from the transmitting to the receiving antenna via multiple paths . The waves interfere, often causing fading and other reception problems . </Li> <Li> Ground waves: At lower frequencies below 2 MHz, in the medium wave and longwave bands, due to diffraction vertically polarized radio waves can bend over hills and mountains, and propagate beyond the horizon, traveling as surface waves which follow the contour of the Earth . This allows mediumwave and longwave broadcasting stations to have coverage areas beyond the horizon, out to hundreds of miles . As the frequency drops, the losses decrease and the achievable range increases . Military very low frequency (VLF) and extremely low frequency (ELF) communication systems can communicate over most of the Earth, and with submarines hundreds of feet underwater . </Li> <Li> Skywaves: At medium wave and shortwave wavelengths, radio waves reflect off conductive layers of charged particles ions in a part of the atmosphere called the ionosphere . So radio waves directed at an angle into the sky can return to Earth beyond the horizon; this is called "skip" or "skywave" propagation . By using multiple skips communication at intercontinental distances can be achieved . Skywave propagation is variable and dependent on atmospheric conditions; it is most reliable at night and in the winter . Widely used during the first half of the 20th century, due to its unreliability skywave communication has mostly been abandoned . Remaining uses are by military over-the - horizon (OTH) radar systems, by some automated systems, by radio amateurs, and by shortwave broadcasting stations to broadcast to other countries . </Li>

Where are radio waves found in the atmosphere