Communications

Radio

Electromagnetic radiation of lower frequency (hence longer wavelength) than visible light or infrared radiation, and consisting of the range of frequencies used for navigation signals, AM and FM broadcasting, television transmissions, cell-phone communications, and various forms of radar.

For radio transmission, information is imparted to a carrier wave by varying (modulating) its amplitude, frequency, or duration. The technology of radio arose from the work of Michael Faraday, James Clerk Maxwell, Heinrich Hertz, Guglielmo Marconi, and others, and improvement followed the development of the vacuum tube, the electronic-tube oscillator, the tuned circuit, and other components. Later innovations have included the replacement of tubes by transistors and of wires by printed circuits. See also radio and radar astronomy.

Phone

Instrument designed for simultaneous transmission and reception of the human voice.

It works by converting the sound waves of the human voice to pulses of electrical current, transmitting the current, and then retranslating the current back to sound. The U.S. patent granted to Alexander Graham Bell in 1876 for developing a device to transmit speech sounds over electric wires is often called the most valuable ever issued. Within 20 years, the telephone acquired a form that has remained fundamentally unchanged for more than a century. The advent of the transistor (1947) led to lightweight, compact circuitry (see cell phone). Advances in electronics have allowed the introduction of a number of “smart” features such as automatic redialing, caller identification, call waiting, and call forwarding. Telephone systems are also a primary access route for the Internet.

TV

Analog signal - Ultra High Frequency UHF, Very High Frequency VHF

Process by which digital signals (which have a binary state) are converted to analog signals (which theoretically have an infinite number of states).

Any system producing significantly greater picture resolution than that of the ordinary 525-line (625-line in Europe) television screen.

Conventional television transmits signals in analog form. Digital HDTV systems, by contrast, transmit pictures and sounds in the form of digital data. These numerical data are broadcast using the same high radio frequencies that carry analog waves, and computer processors in the digital television set then decode the data. Digital HDTV can provide sharper, clearer pictures and sound with very little interference or other imperfections. Of perhaps greater importance, digital television sets will potentially be able to send, store, and manipulate images as well as receive them, thereby merging the functions of the television set and the computer.

Internet