The velocity of electromagnetic waves equals the speed of light. Therefore, we can determine the distance between points in space where the electromagnetic field is in the same phase. This distance is called wavelength. 1 MHz corresponds to the wavelength of about 300m. With increasing frequency, wavelength decreases and vice versa. Radio waves propagate in a vacuum and in the atmosphere and the water surface of the earth for them impenetrable. But due to the effects of reflection and refraction, the relationship between the points of the earth's surface, not having line of sight (in particular, at greater distances).
Transmission is as follows: on the transmitting side is formed by a radio wave (signal) with the desired frequency and power. Further, the transmitted signal modulates a high frequency oscillation. The resulting modulated signal is radiated by the antenna in space. On the receiving side of radio waves induce a modulated signal at the antenna, then it is filtered and demodulated. After the demodulation signal is obtained, similar to that which sent the sending side.
Creator of the first successful system of information exchange via radio (wireless telegraphy) in some countries considered an Italian engineer Guglielmo Marconi. In 1894, under the influence of the work of Nikola Tesla, and Heinrich Hertz, he became interested in problems of transmission of electromagnetic waves and began experiments on signaling by electromagnetic waves. In 1895, Marconi sent a wireless signal to a distance of 3 km. In 1896, having arrived in the UK, he gained recognition and in 1897 received a patent for his invention. The source of transmission was a Hertz oscillator and receiver – instrument Popova, who in turn was based on the device Lodge. In the device Popov Marconi added coherer vacuum created by tubes Branly. Transfer takes place by means of Morse code. Thus, it is clear that his invention would have been impossible without the development of many inventors. Therefore, Marconi, like most authors of major inventions were forerunners. In France, the inventor of wireless telegraphy for a long time considered the creator of the coherer (Branly tube) Eduard Branly. This happened in 1890. In the United States is to be made Nikola Tesla patented in 1893, a radio transmitter and receiver in 1895, and its priority over Marconi's was found in court Order in 1943. In England, in 1894, was the first show broadcast and radio reception at a distance of 40 meters inventor coherer (Branly tube with a shaker), Oliver Joseph Lodge. In Russia, the inventor of the radio is Popov, created in 1895, practical radio. Thus, the personality of the original inventor of radio, then called wireless telegraphy, is contentious, that did not stop radio becoming one the most common means of communication.