The principles of radio communication are as follows. Variable electricity high frequency, created in the transmitting antenna, causes a rapidly changing electromagnetic field in the surrounding space, which propagates in the form of an electromagnetic wave. Reaching the receiving antenna, the electromagnetic wave induces an alternating current in it at the same frequency at which the transmitter operates. The most important stage in the development of radio communications was the creation in 1913 of a continuous-wave generator electromagnetic vibrations. In addition to the transmission of telegraph signals consisting of short and longer pulses of electromagnetic waves, reliable and high-quality radiotelephone communications have become possible - the transmission of speech or music using electromagnetic waves. Radiotelephone communication. In radiotelephone communications, air pressure fluctuations in a sound wave are converted by a microphone into electrical vibrations of the same shape. It would seem that if these vibrations are amplified and fed into an antenna, then it will be possible to transmit speech and music over a distance using electromagnetic waves. However, in reality this method of transmission is not feasible. The fact is that sound frequency oscillations are relatively slow oscillations, and electromagnetic waves of low (sound) frequencies are almost not emitted at all. Modulation. To carry out radiotelephone communication, it is necessary to use high-frequency oscillations intensively emitted by the antenna. Undamped harmonic oscillations of high frequency are produced by a generator, for example a transistor generator. To transmit sound, these high-frequency vibrations are modified, or, as they say, modulated, by electrical vibrations of low (sound) frequency. It is possible, for example, to change the amplitude of high-frequency oscillations with the sound frequency. This method is called amplitude modulation. Figure 127 shows three graphs: a) a graph of oscillations of a high frequency, which is called the carrier frequency; b) a graph of audio frequency oscillations, i.e. modulating oscillations; c) graph of amplitude-modulated oscillations. Without modulation, at best we can control whether the station is working or silent, and that’s all. Without modulation there is no telegraph, telephone or television transmission. Modulation is a slow process. These are changes in a high-frequency oscillatory system in which it manages to make a lot of high-frequency oscillations before their amplitude changes noticeably. Detection. In the receiver, low-frequency oscillations are separated from modulated high-frequency oscillations. This signal conversion process is called detection. The signal obtained as a result of detection corresponds to the sound signal that acted on the transmitter microphone. Once amplified, low frequency vibrations can be turned into sound. The basic principles of radio communication are presented in the block diagram in Figure 128. "i 1. Why is modulation of oscillations needed! 2. What is called detection * of oscillations!
The English scientist James Maxwell, based on studying Faraday's experimental work on electricity, hypothesized the existence in nature of special waves capable of propagating in a vacuum. Maxwell called these waves electromagnetic waves. According to Maxwell's ideas: for any change electric field a vortex magnetic field arises and, conversely, with any change in the magnetic field a vortex appears electric field. Once begun, the process of mutual generation of magnetic and electric fields must continue continuously and capture more and more new areas in the surrounding space (Fig. 42). The process of mutual generation of electric and magnetic fields occurs in mutually perpendicular planes. An alternating electric field generates a vortex magnetic field, an alternating magnetic field generates a vortex electric field.
Electric and magnetic fields can exist not only in matter, but also in vacuum. Therefore, it should be possible to propagate electromagnetic waves in a vacuum.
The condition for the occurrence of electromagnetic waves is accelerated movement electric charges. Thus, a change in the magnetic field occurs
When the current in a conductor changes, and the current changes when the speed of the charges changes, i.e. when they move with acceleration. The speed of propagation of electromagnetic waves in vacuum, according to Maxwell's calculations, should be approximately 300,000 km/s.
The physicist Heinrich Hertz was the first to experimentally obtain electromagnetic waves using a high-frequency spark gap (Hertz vibrator). Hertz also experimentally determined the speed of electromagnetic waves. It coincided with Maxwell's theoretical definition of wave speed. The simplest electromagnetic waves are waves in which electric and magnetic field perform synchronous harmonic oscillations.
Of course, electromagnetic waves have all the basic properties of waves.
They obey the law of wave reflection: angle of incidence equal to angle reflections. When passing from one medium to another, they are refracted and obey the law of refraction of waves: the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant value for two given media and is equal to the ratio of the speed of electromagnetic waves in the first medium to the speed of electromagnetic waves in the second medium and is called the refractive index of the second environment relative to the first.
The phenomenon of diffraction of electromagnetic waves, i.e. deviation of the direction of their propagation from straight-line, is observed at the edge of an obstacle or when passing through a hole. Electromagnetic waves are capable of interference. Interference is the ability of coherent waves to overlap, as a result of which waves in some places reinforce each other, and in other places they cancel each other. (Coherent waves are waves that are identical in frequency and phase of oscillation.) Electromagnetic waves have dispersion, that is, when the refractive index of the medium for electromagnetic waves depends on their frequency. Experiments with the transmission of electromagnetic waves through a system of two gratings show that these waves are transverse.
When an electromagnetic wave propagates, the vectors of tension E and magnetic induction B are perpendicular to the direction of propagation of the wave and mutually perpendicular to each other (Fig. 43).
Opportunity practical application Electromagnetic waves for establishing communication without wires were demonstrated on May 7, 1895 by Russian physicist A. Popov. This day is considered the birthday of radio. To carry out radio communication, it is necessary to ensure the possibility of emitting electromagnetic waves. If electromagnetic waves arise in a circuit of a coil and a capacitor, then the alternating magnetic field is associated with the coil, and the alternating electric field is concentrated between the plates of the capacitor. Such a circuit is called closed (Fig. 44, a).
A closed oscillatory circuit practically does not radiate electromagnetic waves into the surrounding space. If the circuit consists of a coil and two plates of a flat capacitor, then the greater the angle at which these plates are deployed, the more freely the electromagnetic field emerges into the surrounding space (Fig. 44, b). The limiting case of an open oscillatory circuit is the removal of the plates to opposite ends of the coil. Such a system is called an open oscillatory circuit (Fig. 44, c). In reality, the circuit consists of a coil and a long wire - an antenna.
The energy of electromagnetic oscillations emitted (using a generator of continuous oscillations) with the same amplitude of current oscillations in the antenna is proportional to the fourth power of the oscillation frequency. At frequencies of tens, hundreds and even thousands of hertz, the intensity of electromagnetic oscillations is negligible. Therefore, for radio and television communications, electromagnetic waves with frequencies from several hundred thousand hertz to hundreds of megahertz are used.
When transmitting speech, music and other sound signals via radio, use different kinds modulation of high-frequency (carrier) oscillations. The essence of modulation is that high-frequency oscillations generated by the generator change according to the law of low frequency. This is one of the principles of radio transmission. Another principle is the reverse process - detection. When receiving radio signals, it is necessary to filter out low-frequency sound vibrations from the modulated signal received by the antenna of the receiver.
With the help of radio waves, not only sound signals are transmitted over a distance, but also images of objects. A major role in modern navy, aviation and astronautics plays a role in radar. Radar is based on the property of wave reflection from conductive bodies. (Electromagnetic waves are reflected weakly from the surface of a dielectric, but almost completely from the surface of metals.)
Radio communication requires two separate devices: a transmitter and a receiver of electromagnetic waves. To understand the principles of their operation, let’s consider the simplest devices created by the German scientist G. Hertz in 1886.
You see the transmitter device. The wire was cut in half, connecting the resulting sections to a high-voltage transformer. The size of the air gap between the ends of the wires was set so that sparks would often jump through it.
Sparks are an electrical current in the air. Therefore, at the moment they jumped, electrons from the negatively electrified part of the wire rushed to its positively electrified part. This means that a pulsating (alternating) current arose in the wire, and a pulsating (alternating) electromagnetic field around it.
Thus, the wires are transmitter, And transmitting antenna. The electromagnetic field is propagated by electromagnetic waves, so it can be detected at a distance. This requires receiver: two similar pieces of wire placed parallel to the transmitter antenna. Since the energy of the transmitter waves spreads in all directions, and the receiver picks up only a small part of them, sparks in the air gap of the receiver are very small. However, they can be seen with the naked eye in the dark.
Hertz's transmitter and receiver could not be used for long-distance radio communications. The reason for this is the low power of radio waves due to the low frequency alternating current created by sparks. Therefore, it was necessary to create a high-frequency current generator whose power would be sufficient for radio transmissions at a distance of tens and hundreds of kilometers. When this problem was solved, it became possible not only radiotelegraph communication, when words (letter by letter) are transmitted through short and long pulses of Morse code, but also radiotelephone communication, conveying the human voice.
The schematic diagram of radiotelephone communication is shown in the figure below. Firstly, the transmitter contains high frequency generator to provide the required radiation power. It is he who forms the so-called carrier frequency, to which the receiver is tuned. Secondly, the transmitter contains modulator- a device that changes the amplitude or frequency of a carrier wave “in time” with the transmitted voice or music. Thirdly, the transmitter has transmitting antenna.
Easiest to understand amplitude modulation. The high-frequency oscillations created by the generator initially have a constant amplitude (see the figure on the left). The modulator changes the amplitude of the carrier frequency “according to the shape” of the low-frequency signal coming from the microphone. The modulated signal reaches the receiving antenna in the form of waves with varying amplitude (see the figure in the center).
The reverse process is called demodulation. The receiving antenna picks up waves from multiple transmitters operating at different frequencies. Therefore, we need to separate the signal only from a specific transmitter operating at the carrier frequency we select. For this purpose it is used receiving tuning circuit. The signal from “our” transmitter selected by him is sent to demodulator– a device that separates a low-frequency signal useful to the listener from carrier oscillations. It is this signal that goes to the headphones or speakers.
For different consumers of radio communication services, different wave ranges. There are ultra-long, long, medium, short and ultra-short radio waves (see table).
Modern radio communications significantly different compared to ancient times. Innovative devices and techniques that have higher functionality. That is why they are very popular.
Despite the presence of other types of communication, this type still does not lose its relevance today. It is worth noting that it has its own characteristics.
Radio communication itself is the transmission of various types of information through electromagnetic waves that propagate in space between two points: the source itself and the data receiving system.
Radiation occurs using special antennas. As a rule, they are a wire through which high-frequency currents flow. The latter are created directly by the transmitter. Due to the fact that high frequency currents flow through the wire, an electromagnetic field of radio waves is formed in the surrounding space.
To the main characteristics modern radio communications relate:
Modern radio communications are innovative methods of transmitting information over greater distances. Through the use of such technologies it is possible to achieve High Quality signal.
There is a certain classification of radio waves. Depending on this, the transmitter is selected.
The transmitter can be:
This also affects the design features of the device. Modern radio communications involve the use of transmitters that can operate simultaneously on several fixed waves. Also, if necessary, they can be adjusted to absolutely any length in a continuous range.
An important indicator is also the power of information transmission devices. The quality of the transmitted signal directly depends on this parameter.
The signal is defined as the minimum power of high-frequency oscillations that enter the antenna under conditions that there is no modulation and the radiation is continuous. However, this is not all.
Modern radio communications deals with signals that have certain characteristics. As a rule, their voltage can vary over a fairly wide range.
Also, over a minimum period of time, it takes values that exceed the average level.
Conducting thematic projects and industry events is of great importance for the development of the industry.
Such events allow you to:
One of such projects is the exhibition “Communication”. It was traditionally organized by the international complex Expocentre Fairgrounds.
The organizers made sure that the event was held to the maximum high level in B2B format.
Here you can also take part in a business program, which includes consideration of all areas in this area, in particular modern radio communications.
What is the principle of radio communication? Let's start with the fact that to implement it you need to have two devices: a receiver and a transmitter of electromagnetic and sound waves.
Simple instruments needed for work were created in 1886 by G. Hertz. The principle of radio communication is based on classical laws physics. If you cut it into two halves and attach a high-voltage transformer to the sections, an alternating (pulsating) current will arise between them, and an electromagnetic field will appear around it. Wire in in this case is considered both as a transmitter and as a transmitting antenna.
The principle of radio communication is based on the characteristics electromagnetic field. Since waves are necessary for its propagation, it can be caught on considerable distance using the receiver. Its role is played by two pieces of metal wire located parallel to the transmitting antenna. Since the wave energy will spread in different sides, and the receiver manages to catch only part of it, the sparks are small in the airspace. But in the dark they can be seen even without optical instruments.
The principles of radio communication are based on the transmitting devices developed by Hertz, but are suitable only for unimportant distances. This limitation of use is explained by the insignificant power of radio waves. In order to cope with this problem, a high frequency generator was created. With its help, radio waves could travel long distances.
Let's look at the basic principles of radio communications and examples of their practical use. A modern transmitter contains a high frequency generator to create required power radiation. With its help, a carrier frequency is formed that is used by the receiver for tuning. A modern transmitter has a modulator. It is a device that changes the amplitude or frequency of a wave synchronously with music or voice. Required element The transmitter is also the transmitting antenna.
The easiest to understand is amplitude modulation. The high-frequency oscillations that the generator creates have a constant amplitude. With the help of a modulator, it changes “according to the shape” of the low-frequency signal coming from the microphone. The modulated signal reaches the receiving antenna as waves with variable amplitude.
The principle of radio communication is also characterized by demodulation. After the receiving antenna captures the waves, the signal is separated from one transmitter, which operates at the frequency selected as the carrier value. To carry out such transformations, a tuning receiving circuit is used. The signal that is isolated from one transmitter enters the demodulator. This device separates low-frequency oscillations from the high-frequency signal. Then it goes to the loudspeaker or headphones.
Considering the principles of radio communication, we note that waves have different ranges. Currently, medium, ultra-long, short, long, and ultra-short radio waves are used. They are widely used in various fields of electronics:
The principle of modern radio communication involves the transformation of sound vibrations into electrical types using a microphone. The difficulty of transmitting such a signal is that radio communication requires high-frequency vibrations, and sound waves have a low frequency. To solve the problem, powerful antennas are used. For audio frequencies, the superimposition of vibrations is carried out in such a way as to transfer the signal over significant distances.
Modern principles of radio communications and television are based on a radio transmitting device. It has a high frequency generator that converts DC voltage into high frequency harmonic oscillations. The carrier frequency must be constant.
The principles of radio communications and television require a certain structure of the generator. It converts the received messages into an electrical signal, which is used for the constant frequency modulation process. The choice of such a device is based on physical nature of the transmitted signal. In the case of sound, a microphone is used for this; for the transmission of pictures, a transmitting television tube is used. A modulator is necessary to carry out the process of converting a high-frequency signal into a value that corresponds to an audio signal with the transmitted information. One or two stages are also used to amplify the modulated signal. The radiating antenna is designed to emit electromagnetic waves into the surrounding space.
A radio transmitting device is used to receive information that is transmitted thanks to electromagnetic waves emanating from the transmitting antenna of a modern radio transmitter. This device assumes the presence of the following main elements:
Detection is the opposite process of modulation. The detectors are semiconductor devices and vacuum tubes, which have non-linear characteristics. Modeling and detection are the main processes that contribute to the transmission and reception of sound and image, that is, they are associated with the transmission of television images and audio signals.
