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
Subrange name |
Wavelength, m |
Oscillation frequency, Hz |
Ultra long waves Long waves medium waves short waves Meter waves decimeter waves Microwave millimeter waves submillimeter waves |
more than 10 4 m 10 4 —10 3 m 10 3 —10 2 m 10 2 —10 m 10-1 m 1—0.1 m 0.1—0.01 m 0.01—0.001 10 +3 -5 × 10 +5 |
less than 3 × 10 4 3 × 10 4 —3 × 10 5 3 × 10 5 —3 × 10 6 3 × 10 6 —3 × 10 7 3 × 10 7 —3 × 10 8 3 × 10 8 —3 × 10 10 3 x 10 10 —3 x 10 11 3 x 10 11 —6 x 10 12 |
table 2
RF band |
||
range name |
Range limits |
|
main term |
parallel term |
|
1st frequency range 2nd frequency range 3rd frequency range 4th frequency range 5th frequency range 6th frequency band 7th frequency range 8th frequency range 9th frequency band 10th frequency range 11th frequency range 12th frequency range |
Extremely low ELF Ultra-low VLF Infralow FFI Very low VLF Low frequencies LF Middle frequencies Treble Very high VHF Ultra high UHF Ultra high microwave Extremely high EHF Hyper-high GHF |
3-30 Hz 30-300 Hz 0.3-3 kHz 3-30 kHz 30-300 kHz 0.3—3 MHz 3—30 MHz 30—300 MHz 0.3-3 GHz 3-30 GHz 30-300 GHz 0.3—3 THz |
Radio wave range |
||
range name |
Range limits |
|
main term |
parallel term |
|
1st range 2nd range 3rd range 4th range 5th range 6th range 7th range 8th range 9th range 10th range 11th range 12th range |
Decamegameter Megameter Hectokilometer Myriameter Kilometer Hectometric Decameter Meter decimeter centimeter Millimeter decimillimeter |
100-10 mm 10-1 mm 1000-100 km 100-10 km 10-1 km 1—0.1 km 100-10 m 10-1 m 1—0.1 m 10-1 cm 10-1 mm 1—0.1 mm |
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).
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