The physics textbooks contain abstruse formulas on the subject of the range of radio waves, which are sometimes not completely 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 to detect 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 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 radiator of radio waves is an electric conductor with an alternating electric current moving inside. The vibrational energy of a high-frequency generator is distributed into the surrounding space through a radio antenna. The first working source of radio waves was Popov's radio transmitter-receiver. In this device, the function of a high-frequency generator was performed by a high-voltage drive 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 wave range
The waves used in radio communications are in the frequency range 30 kHz - 3000 GHz. Based on the wavelength and frequency, propagation features, the range of radio waves is divided into 10 subbands:
- ADD - super long.
- DW - long.
- NE - medium.
- HF - short.
- VHF - ultrashort.
- MV - meter.
- UHF - decimetric.
- SMV - centimeter.
- MMB - millimeter.
- SMMV - 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 interconnected with the frequency of the AC signal. The frequency ranges of radio waves in the international radio regulations are represented by 12 items:
- ELFs are extremely low.
- VLF - ultra-low.
- INCH - infralow.
- VLF - very low.
- LF - low frequencies.
- MF - mid frequencies.
- HF - high frequencies.
- VHF are very high.
- UHF - ultra high.
- Microwave - ultra high.
- EHF - extremely high.
- GHF - hyperhigh.
With an increase in the frequency of the radio wave, its length decreases, with a decrease in the frequency of the radio wave it increases. Propagation, depending on its length, is an essential property of a radio wave.
The propagation of radio waves from 300 MHz to 300 GHz is called ultra-high microwave due to their relatively high frequency. Even the subbands are very extensive, so they, in turn, are divided into intervals, which include certain ranges of television and broadcasting, for sea and space communications, land and aviation, for radar and radio navigation, for transmitting medical data and so on. Despite the fact that the entire range of radio waves is divided into regions, the indicated boundaries between them are conditional. Plots follow each other continuously, passing one into another, and sometimes overlap.
Features of the propagation of radio waves
Radio wave propagation is the transfer of energy by an alternating electromagnetic field from one piece of space to another. In a vacuum, radio waves propagate at the speed of light. When the environment affects the radio waves, the propagation of radio waves can be difficult. This is manifested in a distortion of signals, a change in the direction of propagation, a deceleration of the phase and group velocities.
Each type of wave is applied differently. Long ones can better get around obstacles. This means that the range of radio waves can propagate along the plane of the earth and water. The use of long waves is widespread in submarines and marine vessels, which allows you to be in touch at any point in the sea. On a wavelength of six hundred meters with a frequency of five hundred kilohertz, receivers of all lighthouses and rescue stations are tuned.
The propagation of radio waves in different ranges depends on their frequency. The shorter the length and the higher the frequency, the more direct the wave path will be. Accordingly, the lower its frequency and the longer the length, the more it is able to go around obstacles. Each range of radio wavelengths has its own propagation characteristics, however, at the border of neighboring ranges, there is no sharp change in distinguishing features.
Distribution Characteristic
Ultra-long and long waves bend around the surface of the planet, spreading by surface rays for thousands of kilometers.
Medium waves are more susceptible to absorption, therefore they are able to cover a distance of only 500-1500 kilometers. When compacting the ionosphere in this range, it is possible to transmit a signal with a spatial beam, which provides communication over several thousand kilometers.
Short waves propagate only at close distances due to the absorption of their energy by the surface of the planet. Spatial ones are capable of repeatedly reflecting from the earth's surface and the ionosphere, traveling long distances, transmitting information.
Ultrashort 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 enveloping the surface of the planet.
In the optical ranges, the transmission of gigantic amounts of information is possible. Most often, a 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 permits from telecommunication inspections.
Modulation principle
In order to transmit information, the radio wave must be modulated by a signal. The transmitter emits modulated radio waves, i.e. modified. Short, medium and long waves have amplitude modulation, so they are referred to as AM. Before modulation, the carrier wave moves with constant amplitude. Amplitude modulation for transmission changes it in amplitude, respectively, of the signal voltage. The amplitude of the radio wave varies in direct proportion to the voltage of the signal. Ultrashort waves are frequency modulated, so they are referred to as FM. Frequency modulation superimposes an additional frequency that carries information. To transmit a signal over a distance, it must be modulated with a higher frequency signal. To receive the signal, you need to separate it from the subcarrier wave. With frequency modulation, less interference is created, however, the radio station is forced to broadcast on VHF.
Factors Affecting the Quality and Efficiency of Radio Waves
The directional radiation method affects the quality and effectiveness of radio wave reception. An example is a satellite dish, which directs radiation to the location of an installed receiving sensor. This method has made significant progress in the field of radio astronomy and made many discoveries in science. He discovered the possibilities of creating satellite broadcasting, wireless data transmission and much more. It turned out that radio waves are able to radiate the Sun, many planets outside our solar system, as well as cosmic nebulae and some stars. It is assumed that outside our galaxy there are objects with powerful radio emissions.
Not only solar radiation, but also weather conditions influence the range of radio waves and the propagation of radio waves. So, meter waves, in fact, do not depend on weather conditions. And the centimeter distribution range is highly dependent on weather conditions. It occurs due to the fact that in the aquatic environment during rain or at an increased level of humidity in the air, short waves are scattered or absorbed.
Also, their quality is affected by obstacles in the way. At such moments, the signal fades, while audibility is significantly impaired or even disappears for a few moments or more. An example is the reaction of the TV to a flying airplane when the image blinks and white stripes appear. This is due to the fact that the wave is reflected from the plane and passes by the antenna of the TV. Such phenomena with TVs and radio transmitters more often occur in cities, since the range of radio waves is reflected in buildings, high-rise towers, increasing the path of the wave.