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NDBs use frequencies between 190 and 1750 kHz in the LF and MF bands which propagate beyond the horizon as ground waves or skywaves much farther than VOR beacons. They transmit a callsign consisting of one to 3 Morse code letters as an identifier. Packet radio – a long-distance peer-to-peer wireless ad-hoc network in which data packets are exchanged between computer-controlled radio modems (transmitter/receivers) called nodes, which may be separated by miles, and maybe mobile. Each node only communicates with neighboring nodes, so packets of data are passed from node to node until they reach their destination using the X.25 network protocol. Packet radio systems are used to a limited degree by commercial telecommunications companies and by the amateur radio community.

Radio transmitters must be licensed by governments, under a variety of license classes depending on use, and are restricted to certain frequencies and power levels. In some classes, such as radio and television broadcasting stations, the transmitter is given a unique identifier consisting of a string of letters and numbers called a call sign, which must be used in all transmissions. Radio, sound communication by radio waves, usually through the transmission of music, news, and other types of programs from single broadcast stations to multitudes of individual listeners equipped with radio receivers. From its birth early in the 20th century, broadcast radio astonished and delighted the public by providing news and entertainment with an immediacy never before thought possible.

Systems that broadcast from satellites can generally be received over an entire country or continent. Older terrestrial radio and television are paid for by commercial advertising or governments. In subscription systems like satellite television and satellite radio the customer pays a monthly fee. In these systems, the radio signal is encrypted and can only be decrypted by the receiver, which is controlled by the company and can be deactivated if there is no current subscription plan. To prevent interference between different users, the emission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union , which allocates bands in the radio spectrum for different uses.

Phased-array radar – a radar set that uses a phased array, a computer-controlled antenna that can steer the radar beam quickly to point in different directions without moving the antenna. Phased-array radars were developed by the military to track fast-moving missiles and aircraft. They are widely used in military equipment and are now spreading to civilian applications. Weather radar – A Doppler radar which maps weather systems and measures wind speeds by reflection of microwaves from raindrops.

The radio- prefix was later used to form additional descriptive compound and hyphenated words, especially in Europe. For example, in early 1898 the British publication The Practical Engineer included a reference to "the radiotelegraph" and "radiotelegraphy". Cellular phone tower shared by antennas belonging to 3 different networks. Radio waves are radiated by electric charges undergoing acceleration. They are generated artificially by time varying electric currents, consisting of electrons flowing back and forth in a metal conductor called an antenna. The non-commercial radios stations are generally free of advertising.

The choice is even greater with web radios and internet radios, as each radio station here has unique stream URLs and there can be no overlaps. Emergency locator beacon – a portable battery powered radio transmitter used in emergencies to locate airplanes, vessels, and persons in distress and in need of immediate rescue. Various types of emergency locator beacons are carried by aircraft, ships, vehicles, hikers and cross-country skiers.

Internet Radio can be received around the globe as long as an internet connection can be established. Submarine communication – When submerged, submarines are cut off from all ordinary radio communication with their military command authorities by the conductive seawater. However radio waves of low enough frequencies, in the VLF and ELF bands are able to penetrate seawater. Navies operate large shore transmitting stations with power output in the megawatt range to transmit encrypted messages to their submarines in the world's oceans.