Shortwave radio Shortwave radio Shortwave radio is radio transmission using shortwave radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band (HF), and generally extends from ; from the high end of the medium frequency band (MF) just above the mediumwave AM broadcast band, to the end of the HF band. Radio waves in the shortwave band can be reflected or refracted from a layer of electrically charged atoms in the atmosphere called the ionosphere. Therefore, short waves directed at an angle into the sky can be reflected back to Earth
Atmosphere of Earth takes place in the troposphere, and it is the only layer that can be accessed by propeller-driven aircraft. Within the five principal layers above, that are largely determined by temperature, several secondary layers may be distinguished by other properties: The average temperature of the atmosphere at Earth's surface is or , depending on the reference. The average atmospheric pressure at sea level is defined by the International Standard Atmosphere as . This is sometimes referred to as a unit of standard atmospheres (atm). Total atmospheric mass is 5.1480×10 kg (1.135×10 lb), about 2.5% less than would be inferred from the