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
Atmospheric pressure Atmospheric pressure Atmospheric pressure, sometimes also called barometric pressure (after the sensor), is the pressure within the atmosphere of Earth (or that of another planet). The standard atmosphere (symbol: atm) is a unit of pressure defined as , equivalent to 760mmHg (torr), 29.92inchesHg, or 14.696psi. The atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth. In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. As elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation. Pressure measures