radio waves

Radio waves  (from  radio... ) , electromagnetic waves with a  wavelength > 500  µm  (frequency < 6 × 10 ¹²  Hz ). R. have a variety of applications:  broadcasting , radiotelephone communications , television , radar , radio meteorology     etc. In all these cases, R. are a means of transmitting one or another information over a distance without wires: speech, telegraph signals, images. R. are used to determine the direction and distance to various objects (radio range finder), to obtain information about the structure of the upper layers of the atmosphere, the Sun, planets, etc.

  Tab. 1. - Division of the radio wave range into subbands

  table 2

Note. The radio frequency bands include the highest frequency and exclude the lowest. Radio wavebands include the shortest length and exclude the longest.

  In the first experiments with the transmission of signals with the help of radio, carried out by A. S.  Popov  in 1895–99, radio was used with a wavelength from 200 to 500  m  (frequencies from 1.5 × 10 ⁶  to 0.6 ×  10 ⁶  Hz ) . Further development of  radio engineering  led to the use of a wider spectrum of electromagnetic waves. The lower limit of the radio spectrum emitted by radio transmitters is on the order of 10 ³ -10 ⁴  Hz.

  There are many natural sources of radiation in nature: stars, including the  Sun , galaxies , metagalaxies , and planets. R.'s research from extraterrestrial sources has allowed us to expand our understanding of the universe (see  Radio astronomy ). Some processes occurring in the earth's atmosphere are also accompanied by the generation of radiation. For example, radiation occurs during a lightning discharge (see  Atmospherics ), when oscillations are excited in the ionospheric plasma. During these processes, R. and lower frequencies (down to fractions of a hertz) are excited.    

  Radio waves of different frequencies propagate differently within the Earth and in outer space (see  Propagation of radio waves ) and, therefore, find various applications in radio communications and in scientific research. Taking into account the characteristics of propagation, generation, and (in part) radiation, the entire radio frequency range is usually divided into a number of subranges:  superlong waves , long waves , medium waves , short waves , meter waves , decimeter waves , centimeter waves , millimeter waves  , and  submillimeter waves  (Table 1). one). The division of R. into ranges in radio communications is established by international        radio communication regulations  (Table 2).