Radio signal
A radio signal , also called a radio signal , is a character or a character string sent by radio waves for the wireless transmission of messages .
species
It is the transmitter generated by electromagnetic vibration of high frequency , in the rhythm -modulated and the antenna are radiated into space. Under the effect of induction , similar but much weaker vibrations occur even in far-away receiving antennas , which after amplification and demodulation largely correspond to the original sequence of characters.
The wireless technology used coded signals to information such as voice and television broadcasts and digital data streams to send wirelessly. In order to avoid excessive growth in radio traffic, the radio frequencies are divided into internationally allocated frequency bands.
There are also naturally generated radio signals, e.g. B. the pulse trains emitted by quasars , the analysis of which can be used to measure the earth and distant universe; the most important of their frequency ranges are protected from technical use. The shock-like wave fronts caused by lightning in thunderstorms are also of natural origin ; they even gave the radio waves their name.
Radio modulated signal
The modulation (imprinting of the message on the carrier wave ) can be done in different ways:
- AM amplitude modulation - by changing the wave energy over time (mostly for medium waves , short waves and image transmission)
- Pulse modulation - transmission of choppy "wave surges" (only rarely used today)
- Frequency modulation FM - change of the carrier frequency in the rhythm of the signal to be transmitted (mostly with FM and TV sound)
- Phase modulation PM - change in phase position .
The exact type of modulation of radio signals is defined according to a scheme of the International Telecommunication Union (ITU), in which, in addition to the four methods listed above, the bandwidth of the signal is usually specified (e.g. 6 kHz on both sides of the target frequency), the type of signal (e.g. E.g. digital) and the type of information (e.g. telephony or radio).
Important applications
Most often, radio signals are used for the wireless transmission of information , in particular:
- Telecommunications : Telegraphy and data transmission, mobile and landline telephony , radio links for the Internet and local computer networks, amateur , aviation and mobile marine radio services
- Broadcast : radio and television , teletext , weather and time services , etc.
- Telemetry : data transmission , e.g. B. from space probes or to control systems
- In science too
- Analysis of natural signals, e.g. B. from the sun and in radio astronomy
- Time of flight measurement of one-way or two-way signals (measurement of time differences in signal propagation): Mostly for purposes of location (especially radar and GPS ), but also electromagnetic distance measurement in geodesy, construction and others.
history
The first successful transmission of a radio signal across the Atlantic took place on December 12, 1901 under the direction of the Italian Guglielmo Marconi. At noon at 12:30 p.m., a floating antenna attached to a kite on the coast of Newfoundland in Canada picked up a signal sent from the English coast in Cornwall: the Morse code for the letter "s". This was one of the major breakthroughs in telecommunications history and paved the way for wireless communications.
See also
Individual evidence
- ↑ www.wissenschaft.de: A hundred years ago the first radio signal went across the Atlantic , accessed in February 2019