page_title: Radio
section_title: Data communications
hierarchical_section_title: Radio / Applications / Data communications
caption_attribution_description: English: A laptop computer, and home wireless router (background), which connects it to the Internet. The laptop has a WiFi wireless modem which transmits data to and receives data from the router, which passes the data on to the Internet through a cable connection provided by an Internet service provider (ISP). The Wifi modem has an automated radio transmitter which transmits packets of digital data by microwaves to a receiver in the router, and the router has a transmitter which transmits data packets back to the laptop. The router may also connect the laptop to other devices on the home network, such as a printer or another computer. The laptop's modem is an add-on card, visible as the turquoise device protruding from the left side.
context_page_description: Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz and 300 gigahertz. They are generated by an electronic device called a transmitter connected to an antenna which radiates the waves, and received by a radio receiver connected to another antenna. Radio is very widely used in modern technology, in radio communication, radar, radio navigation, remote control, remote sensing and other applications.
  In radio communication, used in radio and television broadcasting, cell phones, two-way radios, wireless networking and satellite communication among numerous other uses, radio waves are used to carry information across space from a transmitter to a receiver, by modulating the radio signal in the transmitter. In radar, used to locate and track objects like aircraft, ships, spacecraft and missiles, a beam of radio waves emitted by a radar transmitter reflects off the target object, and the reflected waves reveal the object's location.
context_section_description: Wireless networking – automated radio links which transmit digital data between computers and other wireless devices using radio waves, linking the devices together transparently in a computer network.   Computer networks can transmit any form of data: in addition to email and web pages, they also carry phone calls (VoIP), audio, and video content (called streaming media).   Security is more of an issue for wireless networks than for wired networks since anyone nearby with a wireless modem can access the signal and attempt to log in. The radio signals of wireless networks are encrypted using WPA.
  Wireless LAN (wireless local area network or WiFi) – based on the IEEE 802.11 standards, these are the most widely used computer networks, used to implement local area networks without cables, linking computers, laptops, cell phones, video game consoles, smart TVs and printers in a home or office together, and to a wireless router connecting them to the Internet with a wire or cable connection.  Wireless routers in public places like libraries, hotels and coffee shops create wireless access points (hotspots) to allow the public to access the Internet with portable devices like smartphones, tablets or laptops.  Each device exchanges data using a wireless modem (wireless network interface controller), an automated microwave transmitter and receiver with an omnidirectional antenna that works in the background, exchanging data packets with the router.  WiFi uses channels in the 2.4 GHz and 5 GHz ISM bands with OFDM (orthogonal frequency division multiplexing) modulation to transmit data at high rates.  The transmitters in WiFi modems are limited to a radiated power of 200 mW to 1 watt, depending on country. They have a maximum indoor range of about 150 ft (50 m) on 2.4 GHz and 50 ft (20 m) on 5 GHz.
  Wireless WAN (wireless wide area network, WWAN) – a variety of technologies that provide wireless internet access over a wider area than WiFi networks do – from an office building, to a campus, to a neighborhood, to an entire city.  The most common technologies used are: cellular modems, that exchange computer data by radio with cell towers; satellite internet access; and lower frequencies in the UHF band, which have a longer range than WiFi frequencies.  Since WWAN networks are much more expensive and complicated to administer than WiFi networks, their use so far has generally been limited to private networks operated by large corporations.
  Bluetooth – a very short range wireless interface on a portable wireless device used as a substitute for a wire or cable connection, mainly to exchange files between portable devices and connect cellphones and music players with wireless headphones.  In the most widely used mode, transmission power is limited to 1 milliwatt, giving it a very short range of up to 10 m (30 feet).  The system uses frequency-hopping spread spectrum transmission, in which successive data packets are transmitted in a pseudorandom order on one of 79 1 MHz Bluetooth channels between 2.4–2.83 GHz in the ISM band.  This allows Bluetooth networks to operate in the presence of noise, other wireless devices and other Bluetooth networks using the same frequencies, since the chance of another device attempting to transmit on the same frequency at the same time as the Bluetooth modem is low.  In the case of such a "collision" the Bluetooth modem just retransmits the data packet on another frequency.
  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 may be mobile.  Each node only communicates with neighboring nodes, so packets of data are passed from node to node until they reach their destination.  Uses the X.25 network protocol. Packet radio systems are used to a limited degree by commercial telecommunications companies and by the amateur radio community.
  Text messaging (texting) – this is a service on cell phones, allowing a user to type a short alphanumeric messa
caption: Laptop computer and typical home wireless router (right) connecting it to the Internet
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