Where did it all start

Radio communication, telecommunication by means of radio waves. For radio communication, at the point from which messages are transmitted (radio transmission), a radio transmitter is placed containing a radio transmitter and a transmitting antenna, and at the point at which messages are received (radio reception), a radio receiver is placed containing a receiving antenna and a radio receiver. Harmonic oscillations generated in the transmitter with a carrier frequency belonging to any radio frequency range (see Radio waves) are modulated in accordance with the transmitted message (see Modulation of oscillations). Modulated radio frequency oscillations are a radio signal. From the transmitter, the radio signal enters the transmitting antenna, through which suitably modulated electromagnetic waves are excited in the space surrounding the antenna. spreading radio waves reach the receiving antenna and excite electrical oscillations in it, which are fed further to the radio receiver. Accepted so. the radio signal is very weak, because. only an insignificant part of the radiated energy gets into the receiving antenna (see Propagation of radio waves). Therefore, the radio signal in the radio receiver enters the electronic amplifier, after which it is subjected to demodulation, or detection; as a result, a signal is allocated, similar to the signal with which oscillations with the carrier frequency were modulated in the radio transmitter. Further, this signal (usually additionally amplified) is converted by an appropriate reproducing device into a message that is adequate to the original one. only an insignificant part of the radiated energy gets into the receiving antenna (see Propagation of radio waves). Therefore, the radio signal in the radio receiver enters the electronic amplifier, after which it is subjected to demodulation, or detection; as a result, a signal is allocated, similar to the signal with which oscillations with the carrier frequency were modulated in the radio transmitter. Further, this signal (usually additionally amplified) is converted by an appropriate reproducing device into a message that is adequate to the original one. only an insignificant part of the radiated energy gets into the receiving antenna (see Propagation of radio waves). Therefore, the radio signal in the radio receiver enters the electronic amplifier, after which it is subjected to demodulation, or detection; as a result, a signal is allocated, similar to the signal with which oscillations with the carrier frequency were modulated in the radio transmitter. Further, this signal (usually additionally amplified) is converted by an appropriate reproducing device into a message that is adequate to the original one. which were modulated oscillations with a carrier frequency in the radio transmitter. Further, this signal (usually additionally amplified) is converted by an appropriate reproducing device into a message that is adequate to the original one. which were modulated oscillations with a carrier frequency in the radio transmitter. Further, this signal (usually additionally amplified) is converted by an appropriate reproducing device into a message that is adequate to the original one.

At the place of reception, electromagnetic oscillations from extraneous sources of radio emission can be superimposed on the radio signal, which can interfere with the correct reproduction of the message and are therefore called radio interference. An adverse effect on the quality of radio communication can also be caused by a change in the time of attenuation of radio waves along the propagation path from the transmitting antenna to the receiving antenna (see Fading) and the propagation of radio waves simultaneously along two or more trajectories of different lengths; in the latter case, the electromagnetic field at the place of reception is the sum of radio waves mutually displaced in time, the interference of which also causes distortion of the radio signal. Therefore, these phenomena are also classified as radio interference. Their influence on the reception of radio signals is especially great when communicating over long distances.

The propagation of radio waves in open space makes it possible, in principle, to receive radio signals transmitted over radio communication lines by persons for whom they are not intended (radio interception, radio eavesdropping); this is the disadvantage of radio communications in comparison with telecommunications via cables, radio waveguides, and other closed lines. The secrecy of telephone conversations and telegraph communications, provided for by the USSR Communications Regulations, the relevant rules of other countries, and international agreements, is ensured, when necessary, by the use of automatic means of classifying radio signals (coding, etc.).

Attempts to implement radio communication were made by T. A. Edison in the 80s. 19th century (he received the corresponding patent), before the discovery of electromagnetic waves in 1888 by G. Hertz; although Edison's work did not have practical success, they contributed to the emergence of other works aimed at implementing the idea of ​​​​wireless communication. Hertz created a spark emitter of electromagnetic waves, which (with subsequent various improvements) for several decades remained the most common type of radio transmitter in radio communications. The possibility and basic principles of radio communication were described in detail by W. Crookes in 1892, but at that time the imminent implementation of these principles was not yet foreseen. The development of radio communications began after A. S. Popov and a year later G. Marconi created sensitive receivers in 1895, quite suitable for signaling without wires, i.e. for radio communication. The first public demonstration by Popov of the work of the radio equipment he created and the wireless transmission of signals with its help took place on May 7, 1895, which gives reason to consider this date as the actual day of the appearance of radio communications.

Popov's radio receiver not only turned out to be suitable for radio communication, but (with some additional nodes) was first successfully used by him in the same 1895 for automatic recording of lightning discharges, which marked the beginning of radio meteorology. In the countries of Western Europe and the United States, active use of radio communications for commercial purposes was launched. Marconi registered the Wireless Telegraphy and Signaling Company in England in 1897, founded the American Wireless and Telegraph Company in 1899, and in 1900 the International Maritime Communications Company. In December 1901, he carried out a radiotelegraphic transmission across the Atlantic Ocean. In 1902, the production of equipment for radio communications in Germany was organized by A. Slaby (together with G. Arko) and also by C. F. Braun. The obvious great importance of radio communications for military fleets and for maritime transport, as well as the humanistic role of radio communications (in rescuing people from ships that have crashed) stimulated its development throughout the world. At the 1st International Administrative Conference in Berlin in 1906, with the participation of representatives of 29 countries, the radio regulations and the international convention were adopted, which entered into force on July 1, 1908. The regulations fixed the distribution of radio frequencies between different radio services (see below). The Radio Registration Bureau was founded and an international SOS distress signal was established. At an international conference in London in 1912, the distribution of frequencies was somewhat changed, the regulations were clarified, and new services were established: a radio beacon, the transmission of weather reports, and the transmission of accurate time signals. By decision of the radio conference of 1927, the use of spark radio transmitters, which created radiation in a wide frequency spectrum and thereby hindered the effective use of radio frequencies, was prohibited; spark transmitters were left only to transmit distress signals, since the wide spectrum of radio waves emitted increases the likelihood of their reception. From 1915 to the 50s. equipment for radio communication developed mainly on the basis of vacuum tubes; then transistors and other semiconductor devices were introduced. From 1915 to the 50s. equipment for radio communication developed mainly on the basis of vacuum tubes; then transistors and other semiconductor devices were introduced. From 1915 to the 50s. equipment for radio communication developed mainly on the basis of vacuum tubes; then transistors and other semiconductor devices were introduced.

Until 1920, radio communication used mainly waves with a length of hundreds of meters to tens of kilometers. In 1922, radio amateurs discovered the property of decameter (short) waves to propagate to any distance due to refraction in the upper atmosphere and reflection from them. Soon, such waves became the main means of long-range radio communications. signals coming from great distances are sensitive receivers and large, relatively highly directional antenna structures, occupying a large area, the so-called. antenna field (similar structures are also used to radiate decameter waves). To reduce radio interference, receiving equipment is placed away from cities and away from radio transmitters, at special receiving radio centers. Radio transmitting devices are also grouped - at transmitting radio centers. Both of them are connected with the central telegraph located in the city, from where the transmitted signals come and where the received signals are broadcast.

In the 30s. meter waves were mastered, and in the 40s - decimeter and centimeter waves, propagating mostly rectilinearly, without bending around the earth's surface (i.e., within the line of sight), which limits the direct connection on these waves to a distance of 40-50 km. Since the width of the frequency ranges corresponding to these wavelengths - from 30 MHz to 30 GHz - is 1000 times greater than the width of all frequency ranges below 30 MHz (waves longer than 10 m), they allow the transmission of huge information flows, realizing multi-channel communication. At the same time, the limited propagation range and the possibility of obtaining a sharp directivity with an antenna of a simple design make it possible to use the same wavelengths at many points without mutual interference. Transmission over considerable distances is achieved by the use of multiple retransmissions in radio relay lines or with the help of communication satellites located at high altitudes (about 40,000 km) above the Earth (see Space communications). Allowing tens of thousands of telephone conversations to be conducted simultaneously over long distances and dozens of television programs to be transmitted, radio relay and satellite communications are incomparably more effective in their capabilities than conventional long-distance radio communications on decameter waves, the significance of which decreases accordingly (for example, it retains the role of a useful reserve , as well as the role of a means of communication in directions with low information flows).

With a high radio transmitter power (tens of kilowatts), radio communication at meter waves in a narrow frequency band (several kHz) is possible at distances of ~ 1000 km due to wave scattering in the ionosphere (see Ionospheric radio communication). They also use the reflection of radio waves from the ionized traces of meteors that burn up in the upper atmosphere (see Meteor radio communication), but the transmission of information is intermittent, which does not allow telephone conversations.

A small part of the radiation energy at decimeter and centimeter waves can also propagate beyond the horizon (to distances of hundreds of kilometers) due to the electrical inhomogeneity of the troposphere. This makes it possible, with a relatively high power of transmitters (of the order of several kW), to build radio-relay communication lines with a distance between intermediate stations of 200-300 km or more (with a narrowing of the frequency spectrum of the radiation, i.e., a decrease in the amount of transmitted information, see Tropospheric radio communication).

Radio links are used to transmit telephone messages, telegrams, digital information streams and facsimiles, as well as to transmit television programs (usually on meter and shorter wavelengths). According to the purpose and range of action, international and intra-union nationwide radio communication lines are distinguished. Intra-union lines are divided into trunk lines (between the capital of the USSR and the capitals of the Union republics, krai and regional centers, as well as between the latter) and zone lines (intra-regional and intra-district). The development of radio communication lines is planned taking into account the inclusion of radio communications in the Unified Automated Communication System of the country.

Organizational and technical measures and means for establishing radio communications and ensuring its systematic functioning form radio communications services, distinguished by purpose, range, structure, and other features. In particular, there are services: terrestrial and space radio communications (space radio communications include all types of radio communications using one or more satellites or other space objects); fixed (between certain points) and mobile (between mobile and fixed radio stations or between mobile radio stations); broadcasting and television. For production and special official needs, there are departmental radio communication services in some ministries and organizations (for example, in civil aviation, railway, sea and river transport, fire protection services, police, medical service of cities), as well as intra-production communications in industrial and agricultural areas. enterprises, in some institutions, etc. (see also Radio station of grassroots communications). Radio communications are of great importance in the armed forces.