Atmospheric diffraction type of dust in the atmosphere. The ionosphere is a layer of partially ionized gases high above the majority of the Earth's atmosphere; these gases are ionized by cosmic rays originating on the sun. When radio waves travel into this zone, which commences about 80 kilometers above the earth, they experience diffraction in a manner similar to the visible light phenomenon described above. In this case some of the electromagnetic energy is bent in a large arc, such that it can return to the Earth's surface at a very distant point (on the order of hundreds of kilometers from the
Through-the-earth mine communications Through-the-earth mine communications Through-the-Earth (TTE) signalling is a type of radio signalling used in underground mines and caves that uses low-frequency waves to penetrate dirt and rock, which are opaque to higher-frequency conventional radio signals. In mining, these lower-frequency signals can be relayed underground through various antennas, repeater or mesh configurations, but communication is restricted to line of sight to these antenna and repeaters systems. Through-the-Earth transmission can overcome these restrictions by using ultra-low frequency (300–3000 Hz) signals, which can travel through several hundred feet of rock strata. The antenna cable can be located on the surface only at a