In 1887, Heinrich Hertz demonstrated that electromagnetic energy can be sent into space in the form of radio waves that pass through the atmosphere around the speed of light.This discovery has helped develop principles of radio communication, used by today.Moreover, scientists have proved that radio waves are electromagnetic in nature, and their main characteristic - it is the frequency at which the energy varies between electric and magnetic fields.Frequency in Hertz (Hz) is related to the wavelength λ, which is the distance which a radio wave passes during one oscillation.Thus, the following formula: λ = C / F (where C is the speed of light).
The principles are based on radio transmission of information-carrying radio waves.They can transmit voice or digital data.For this station must have:
- acquiring device information into an electrical signal (e.g., a microphone).This signal is called a primary frequency band in the conventional audio range.
- Modulator entering information into the bandwidth of the signal on the selected frequency radio.
- transmitter signal power amplifier, which sends it to the antenna.
- from electrically conductive antenna rod of a certain length that will radiate electromagnetic radio waves.
- amplifier signal at the receiver side.
- demodulator which is capable of restoring the original information from the received radio signal.
- Finally, a device for reproducing the transmitted information (eg, a speaker).
Principles radio
modern principle of radio was conceived at the beginning of the last century.While radio developed mainly for voice and music.But very soon have the opportunity to use the principles of radio communication for the transmission of more complex information.For example, such as text.This led to the invention of the telegraph code.
General for voice, music or telegraph is that basic information is encoded in the audio signals, which are characterized by amplitude and frequency (Hz).Humans can hear sounds in the range from 30 Hz to about 12 000 Hz.This range is called a sound spectrum.
radio frequency spectrum is divided into different frequency bands.Each of them has specific characteristics in terms of radiation attenuation and the atmosphere.Isolate as described in the table below communications applications that run in a particular range.
| LF- | range from 30 kHz to 300 | kHz | mainly used for aircraft, lighthouses, navigation, and to transmit information. |
| FM- | range from 300 kHz to 3000 | kHz | used for digital broadcasting. |
| RF | range from 3000 kHz | to 30000 kHz | This range is well suited for medium and long terrestrial radio. |
| VHF band | 30,000 kHz | to 300,000 kHz | VHF is typically used for terrestrial broadcasting and communications of ships and aircraft |
| UHF-band | 300,000 kHz | to 3,000,000 kHz | With this range of work satellite positioning systems, and mobile phones. |
Today it is difficult to imagine that humanity would make no radio, which has found its application in many modern devices.For example, the principles of radio and television are used in mobile phones, keyboard, GPRS, Wi-Fi, wireless computer networks and so on.
