презентация по теме "Происхождение средств связи"

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Radio (Latin radio - emit, beaming ← radius - beam) - a kind of wireless communication, in which as a carrier signal using radio waves propagating freely in space.

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THE HISTORY OF THE INVENTION OF RADIO Creator of the first successful system of information exchange via radio (wireless telegraphy) is an Italian engineer Guglielmo Marconi (1895). However, work by Marconi were met without enthusiasm. Russia has traditionally been the inventor of wireless telegraphy Popov, but neither the one nor the other is not quite true. Marconi, in fact combined transmitter and receiver Heinrich Hertz Popov, in a single device. In the first experiments on the radio held in the physics laboratory, and then in the garden Landmine officer class, the receiver detects the emission of radio signals sent from a transmitter to a distance of 60 meters in the United States is considered the inventor of radio Nikola Tesla, patented in 1893, radio, and in 1895 , the receiver, and its priority over Marconi was recognized by the courts in 1943. This is because the device is designed Tesla allowed modulated acoustic signal transmitter oscillator circuit, to carry the radio signal transmission and to take it a receiver that converts the signal into an acoustic sound.

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The same design have all modern radio devices, which are based on the resonant circuit. While the design of Marconi and Popov were primitive and allows only the alarm function, including using Morse code. In France, the inventor of wireless telegraphy has long been considered the creator of the coherer ( Branly tube) (1890) Edouard Branly . In India, in the millimeter radio program in November 1894, shows Sir Jagadish Chandra Bose. In England, in 1894, the first shows broadcast and reception in a distance of 40 meters inventor of the coherer (a tube with a shaker Branly ) Oliver Joseph Lodge. The first is the inventor of the modes of transmission and reception of electromagnetic waves (which for a long time called " Hertzian waves - Hertzian Waves»), he is a pioneer of the German scientist Heinrich Hertz (1888 ). The invention of radio has given rise to such sciences as radio astronomy, radiometrologiya , radio navigation, radio reconnaissance, electronic counter.

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Nikola Tesla demonstrated the transmission of high frequency energy in a lecture at Columbia College in New York, 1891

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PRINCIPLE OF OPERATION The transfer is as follows: on the transmit side, it produces the required characteristics (frequency and amplitude of the signal). Then the transmitted signal modulates a high-frequency oscillation (carrier). The resulting modulated signal transmitting antenna in space. On the receiving side of the radio waves induce a modulated signal in the antenna, then it is demodulated (detected) and filtered by LPF (thus getting rid of high-frequency component - the carrier). Thus, there is the extraction of the desired signal. The resulting signal can be different from the transmitted transmitter (distortion due to noise and interference).

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FREQUENCY BANDS: Main article: Frequency According to the decision of the ITU to distinguish the following frequency bands: [1] Very low frequency (miriametrovye wave) - f = 3-30 kHz ( λ =10-100 ) Low frequencies (wave kilometer) - f = 30-300 kHz ( λ = 1-10 km) Mids (hectometer wave) - f = 0,3-3 MHz ( λ = 0,1-1 km) Treble (decameter wave) - f = 3-30 MHz ( λ = 10-100 m) Very high frequency (meter waves) - f = 30-300 MHz ( λ = 1-10 m) Ultra-high frequency (microwaves) - f = 0,3-3 GHz ( λ = 10-100 cm) Ultra-high frequency (microwaves) - f = 3-30 GHz ( λ = 1-10 cm) The extremely high frequency (millimeter wave) - f = 30-300 GHz ( λ = 0,1-1 cm) In practice, radio and television, a simplified classification of Radio: Extra-long wave (ADD) - miriametrovye wave Long wave (LW) - kilometer wave Medium wave (MW) - hectometer wave Short Wave (SW) - decameter wave Very high frequency (VHF) - high-frequency waves, whose wavelength is less than 10 m

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Depending on the range of the radio waves have their own characteristics and laws of propagation: DV are strongly absorbed by the ionosphere, the main significance Surface waves that propagate, skirting the ground. Their intensity with distance from the transmitter decreases relatively quickly. NE ionosphere are strongly absorbed in the afternoon, and the area of the surface is determined by the wave of the evening well reflected from the ionosphere, and the area of the reflected wave is determined. HF spread only through reflection by the ionosphere, so around there is the so-called transmitter. radio quiet zone. Happy is better distributed over short waves (30 MHz), at night - a long (3 MHz). Short waves can propagate over long distances at low power transmitter. VHF distributed linearly and are usually not reflected by the ionosphere, but under certain conditions can bend around the globe because of the difference in air density at different altitudes. Easy to bend around obstacles and have high penetrating ability. HF does not bend around obstacles, are spread in a straight line. Used in WiFi , cellular, etc. EHF not bend around obstacles, which covers most of obstacles, are distributed in a straight line. Used for satellite communications. Hyper-high frequency does not bend around obstacles, like the reflected light traveling in a straight line. Use is limited.

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WAVE PROPAGATION Radio waves travel in a vacuum and in the atmosphere, solid earth and waters they are opaque. However, due to the effects of diffraction and reflection, the relationship between the points of the earth's surface that have no direct line of sight (in particular, at a great distance). Radio wave propagation from the source to the receiver can occur in several ways at once. This is called multipath propagation. Due to multipath and change parameters of the medium, there are fading (born fading) - changes in the level of the received signal in time. Multipath signal level changes are a result of interference, that is, the received electromagnetic field is the amount of time shifted radio range.

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THANK YOU FOR YOUR ATTENTION! Работу выполнили: Ахметсафина Л., Егорова Е. ученицы 8 «б» класса. Проверила : Галямова Г.К.