In 1887, Heinrich Hertz proved that electromagnetic energy can be sent to space in the form of radio waves that travel through the atmosphere at about the speed of light. This discovery helped develop the principles of radio communications that are used today. In addition, the scientist proved that radio waves have an electromagnetic nature, and their main characteristic is the frequency at which the energy oscillates between electric and magnetic fields. The frequency in hertz (Hz) is related to the wavelength λ, which is the distance that a radio wave travels during one oscillation. Thus, the following formula is obtained: λ = C / F (where C is equal to the speed of light).
The principles of radio communication are based on the transmission of information-bearing radio waves. They can transmit voice or digital data. For this, the radio station must have:
- A device for collecting information into an electrical signal (such as a microphone). This signal is called the main frequency band in the normal audio range.
- Modulator for entering information into the frequency band of the signal at the selected radio frequency.
- A transmitter, a signal power amplifier that sends it to an antenna.
- An antenna from a conductive rod of a certain length that will emit an electromagnetic radio wave.
- Signal amplifier on the receiver side.
- A demodulator that will be able to recover the original information from the received radio signal.
- Finally, a device for reproducing transmitted information (for example, a speaker).
Radio principles
The modern principle of radio communications was conceived at the beginning of the last century. At that time, radio was designed primarily for voice and music. But very soon it became possible to use the principles of radio communications to transmit more complex information. For example, such as text. This led to the invention of the Morse telegraph.
Common to voice, music or telegraph is that the basic information is encrypted in sound signals, which are characterized by amplitude and frequency (Hz). People can hear sounds ranging from 30 Hz to about 12,000 Hz. This range is called the sound spectrum.
The radio frequency spectrum is divided into different frequency ranges. Each of which has specific characteristics with respect to radiation and attenuation in the atmosphere. Allocate communication applications described in the table below, which operate in a particular range.
| LF range | from 30 kHz | up to 300 kHz | It is mainly used for aircraft, lighthouses, navigation, as well as for the transmission of information. |
| FM band | from 300 kHz | up to 3000 kHz | Used for digital broadcasting. |
| High frequency range | from 3000 kHz | up to 30000 kHz | This range is widely suitable for medium and long-range terrestrial radio communications. |
| VHF band | from 30000 kHz | up to 300000 kHz | VHF is commonly used for terrestrial broadcasting and communications of ships and aircraft |
| UHF range | from 300000 kHz | up to 3,000,000 kHz | Using this spectrum, satellite positioning systems, as well as mobile phones, work. |
Today it is difficult to imagine what humanity would do without radio communications, which have found their application in many modern devices. For example, the principles of radio and television are used in mobile phones, keyboards, GPRS, Wi-Fi, wireless computer networks, and so on.