In physics textbooks, abstruse formulas are given on the topic of the range of radio waves, which are sometimes not fully understood even by people with special education and work experience. In the article we will try to understand the essence without resorting to difficulties. The first person to discover radio waves was Nikola Tesla. In his time, where there was no high-tech equipment, Tesla did not fully understand what this phenomenon was, which he later called the ether. An alternating current conductor is the beginning of a radio wave.
Radio wave sources
Natural sources of radio waves include astronomical objects and lightning. An artificial emitter of radio waves is an electrical conductor with an alternating electric current moving inside. The oscillatory energy of the high-frequency generator is distributed into the surrounding space by means of a radio antenna. The first working source of radio waves wasPopov's radio transmitter-receiver. In this device, the function of a high-frequency generator was performed by a high-voltage storage device connected to an antenna - a Hertz vibrator. Artificially created radio waves are used for stationary and mobile radar, broadcasting, radio communications, communication satellites, navigation and computer systems.
Radio waveband
The waves used in radio communications are in the frequency range of 30 kHz - 3000 GHz. Based on the wavelength and frequency of the wave, propagation features, the radio wave range is divided into 10 sub-bands:
- SDV - extra long.
- LW - long.
- NE - average.
- SW - short.
- VHF - ultra short.
- MV - meters.
- UHF - decimeter.
- SMV - centimeter.
- MMV - mm.
- SMMW - submillimeter
Radio frequency range
The spectrum of radio waves is conditionally divided into sections. Depending on the frequency and length of the radio wave, they are divided into 12 subbands. The frequency range of radio waves is related to the frequency of the AC signal. The frequency ranges of radio waves in the international radio regulations are represented by 12 names:
-
radio waves propagation of radio waves ELF - extremely low.
- VLF - ultra-low.
- INCH - infra-low.
- VLF - very low.
- LF - low frequencies.
- mid - middle frequencies.
- HF− high frequencies.
- VHF - very high.
- UHF - ultra high.
- Microwave - ultra high.
- EHF - extremely high.
- HHF - hyper high.
When the frequency of the radio wave increases, its length decreases, when the frequency of the radio wave decreases, it increases. Propagation depending on its length is the most important property of a radio wave.
The propagation of radio waves 300 MHz - 300 GHz is called ultra-high microwave due to their rather high frequency. Even the subbands are very extensive, so they, in turn, are divided into intervals, which include certain ranges for television and radio broadcasting, for maritime and space communications, terrestrial and aviation, for radar and radio navigation, for medical data transmission and so on. Despite the fact that the entire range of radio waves is divided into regions, the indicated boundaries between them are conditional. The sections follow each other continuously, passing one into another, and sometimes overlap.
Features of radio wave propagation
The propagation of radio waves is the transfer of energy by an alternating electromagnetic field from one part of space to another. In a vacuum, a radio wave travels at the speed of light. Radio waves may be difficult to propagate when exposed to the environment. This manifests itself in signal distortion, a change in the direction of propagation, and a slowdown in phase and group velocities.
Each of the wave typesapplied in different ways. Long ones are better able to bypass obstacles. This means that the range of radio waves can propagate along the plane of land and water. The use of long waves is widespread in submarines and marine vessels, which allows you to be in touch at any location at sea. The receivers of all beacons and life-saving stations are tuned to a 600-meter-long wave with a frequency of 500 kilohertz.
The propagation of radio waves in different ranges depends on their frequency. The shorter the length and the higher the frequency, the straighter the path of the wave will be. Accordingly, the lower its frequency and the greater the length, the more capable it is of bending around obstacles. Each range of radio wave lengths has its own propagation characteristics, but there is no sharp change in distinguishing features at the border of neighboring ranges.
Propagation characteristic
Ultra-long and long waves bend around the surface of the planet, spreading by surface rays for thousands of kilometers.
Medium waves are subject to stronger absorption, so they can only cover a distance of 500-1500 kilometers. When the ionosphere is dense in this range, it is possible to transmit a signal by a space beam, which provides communication over several thousand kilometers.
Short waves propagate only over short distances due to the absorption of their energy by the surface of the planet. Spatial ones are able to repeatedly reflect from the earth's surface and the ionosphere, overcome long distances,by transmitting information.
Ultra-short are capable of transmitting a large amount of information. Radio waves of this range penetrate through the ionosphere into space, so they are practically unsuitable for terrestrial communications. Surface waves of these ranges are emitted in a straight line, without bending around the surface of the planet.
Giant volumes of information can be transmitted in optical bands. Most often, the third range of optical waves is used for communication. In the Earth's atmosphere, they are subject to attenuation, so in reality they transmit a signal at a distance of up to 5 km. But the use of such communication systems eliminates the need to obtain permission from the telecommunication inspectorates.
Modulation principle
In order to transmit information, a radio wave must be modulated with a signal. The transmitter emits modulated radio waves, that is, modified. Short, medium and long waves have amplitude modulation, so they are referred to as AM. Before modulation, the carrier wave moves with a constant amplitude. Amplitude modulation for transmission changes it in amplitude, corresponding to the voltage of the signal. The amplitude of the radio wave changes in direct proportion to the signal voltage. Ultrashort waves are frequency modulated, so they are referred to as FM. Frequency modulation imposes an additional frequency that carries information. To transmit a signal over a distance, it must be modulated with a higher frequency signal. To receive a signal, you need to separate it from the subcarrier wave. With frequency modulation, less interference is created, but the radio station is forcedbroadcast on VHF.
Factors affecting the quality and efficiency of radio waves
The quality and efficiency of radio wave reception is influenced by the method of directional radiation. An example would be a satellite dish that sends radiation to the location of an installed receiving sensor. This method allowed significant progress in the field of radio astronomy and made many discoveries in science. He opened up the possibility of creating satellite broadcasting, wireless data transmission, and much more. It turned out that radio waves are capable of emitting the Sun, many planets outside our solar system, as well as space nebulae and some stars. It is assumed that there are objects outside our galaxy that have powerful radio emissions.
The range of the radio wave, the propagation of radio waves is influenced not only by solar radiation, but also by weather conditions. So, meter waves, in fact, do not depend on weather conditions. And the range of propagation of centimeter strongly depends on weather conditions. This is due to the fact that short waves are scattered or absorbed by the aquatic environment during rain or with an increased level of humidity in the air.
Also, their quality is affected by obstacles on the way. At such moments, the signal fades, and the audibility deteriorates significantly or disappears altogether for a few moments or more. An example would be the TV's response to an overflying aircraft when the image flickers and white bars appear. This happens due tothe fact that the wave is reflected from the aircraft and passes by the TV antenna. Such phenomena with televisions and radio transmitters are more likely to occur in cities, since the radio wave range is reflected on buildings, high-rise towers, increasing the path of the wave.
