How is information transmitted on radio waves
What is the role of radio waves in the transmission of information?
Radio waves form the decisive technical basis for mobile telephony. In a sense, they serve as a means of transport that transports information at the speed of light. The call or data signals are digitized and converted into high-frequency electromagnetic fields.
Electromagnetic fields can be found everywhere in our environment. Some of them have a natural origin; for example the fields that occur during a thunderstorm, but also the light of the sun. Technically generated electromagnetic fields arise where electricity flows. They are generated, for example, by radio and television sets, but also by hair dryers, microwave ovens and cell phones.
Electromagnetic fields and frequency ranges
Electromagnetic fields differ in their wavelength: the shorter the wavelength, the higher thefrequency. A distinction is made between low-frequency electrical and magnetic fields in the frequency range between 0 Hertz and 10 kilohertz and between high-frequency electromagnetic fields in the frequency range from 10 kilohertz to 300 gigahertz. The frequency range around 900 megahertz and around 1,800 megahertz is used for GSM. UMTS transmits in the frequency range between 1,900 and 2,100 megahertz. LTE cellular networks use frequencies in the 800 megahertz, 1.8 gigahertz and 2.6 gigahertz ranges. LTE networks in the 700 megahertz range will be added in the future.
Transmission of radio waves in cellular communications
Cell phones and base stations work in a similar way to a loudspeaker when transmitting radio waves. While the loudspeaker converts electrical energy into sound waves, cell phones and base stations send electromagnetic fields as radio waves to the respective receiver.
In the case of the mobile radio base station, this transmission of the radio waves takes place mainly horizontally. The main direction of transmission of the waves is comparable to the cone of light from a lighthouse. Therefore, only a few radio waves reach places directly below the antenna. In addition, the strength of the radio waves decreases rapidly as the distance from the antenna increases.
Propagation and influencing factors of radio waves
Since radio waves propagate in a straight line, they have natural and artificial limits. Buildings, mountains, narrow valleys or narrow streets can become so-calledShadowingand thus lead to poor reception. Reinforced concrete or metal-coated panes also have this effect. Weather influences such as rain or snow can also be a factordamping causing radio waves.
Similar to light waves, radio waves are not only shadowed, but also reflected. Thesereflection ensures that the waves also "illuminate" areas that cannot be reached directly because of the shadows. Due to reflection, a cell phone signal reaches the cell phone in a roundabout way from the base station. For this reason, a mobile phone user usually has reception even if there is no direct visual contact with the base station.
If radio waves hit objects, some of the waves are picked up by the object, that isabsorbed. Accordingly, there is only subdued reception behind the object. Since the human body also absorbs radio waves through the skin, the SAR limit has been set to protect health. This Specific Absorption Rate (SAR) indicates how much electromagnetic energy is absorbed by the body.
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