Radio technology dates back to the latter part of the 19th century, when its development revolutionized communications, allowing almost instantaneous wireless communications across great distances. This type of communication had previously required telegraphs or even slower forms of communication, such as overland mail, that could take days or even months to reach their destination. Today, many radio gadgets make use of radio waves in their operation, and many of them are designed to facilitate some type of communication. Radio gadgets can, however, take many other forms, such as radar, microwave ovens, and diathermy, a technique used for highly delicate surgical tasks, such as sealing microscopic blood vessels during microsurgery.
Nearly everyone is familiar with radio receivers that can pick up AM or FM radio signals. These devices are found in nearly every automobile, and billions of portable radio receivers for personal use are used every day all over the world. Music, news, public service, and other programming are broadcast by radio stations for reception by these devices. Broadcast television also uses radio waves to transmit signals. Beyond these familiar uses, radio is used in a number of other types of technology that are found all around us.
Two-way radios are designed to operate on a specific frequency over short ranges to facilitate direct communication between individuals. These radios can operate in pairs or in groups, and most are capable of operating on a variety of frequencies, called channels. Two-way radios are used to communicate with spacecraft, satellites, airplanes, and ships all over the world on a daily basis. Cell phones use radio waves to connect to cellular phone networks.
Another common type of radio gadget is radar, which generates high power radio waves that are reflected back to the source of the transmission where they are picked up by a receiver. By measuring the time between transmission and reception, it is possible to determine the distance to the detected object, and sophisticated radar systems can distinguish objects by size and track their speed and direction of travel. Radar technologies are essential to national defense and to the management of air and sea traffic as well. Police sometimes use small radar devices to measure the speed of vehicles on roads in order to enforce speed limits. These same devices, often called radar guns, are often used during baseball games to measure the speed of a pitch.
Microwave ovens are also radio gadgets and use a type of very short wavelength radio wave to heat food by exciting the water molecules it contains. The waves cause the molecules to vibrate rapidly, resulting in an increase in temperature, which cooks the food. Microwave radios can also be used for communication, and radio waves are used in microsurgery to cauterize tiny blood vessels.
Many other types of radio gadgets, such as garage door openers, are common in everyday life. Hobbyists use radio control to remotely operate model cars, airplanes, and boats. This same type of technology is used by law enforcement and military organizations to control bomb disposal and for reconnaissance robots and vehicles. Wireless networking uses radio transmission to connect computers and peripheral devices to each other and the Internet. Radio has proven to be useful for other new technologies as well, which have not yet been commercially developed or progressed beyond the conceptual stages, such as the wireless transmission of small amounts of power, the propulsion of interplanetary spacecraft, and the positional stabilization of very small objects in zero or negligible gravity.