Another technological triumph is the cell phone, a radio-linked device that is taking the world by storm. Old-style mobile telephones received their signals from a single powerful transmitter that covered an area about 50 miles in diameter, an interference-prone method that provided enough channels to connect only a couple of dozen customers at a time. Cellular technology, by contrast, uses low-powered base stations that serve "cells" just a few square miles in area. As a customer moves from one cell to another, the phone switches from a weakening signal to a stronger one on a different frequency, thus maintaining a clear connection. Because transmissions are low powered, frequencies can be reused in nonadjacent cells, accommodating thousands of callers in the same general area. Although the principles of cellular telephony were worked out at Bell Labs in the 1940s, building such systems had to await the arrival of integrated circuits and other microelectronic components in the 1970s. In the United States, hundreds of companies saw the promise of the business, but government regulators were very slow in making a sufficiently broad band of frequencies available, delaying deployment considerably. As a result, Japan and the Scandinavian countries created the first cellular systems and have remained leaders in the technology. At the start there was plenty of room for improvement. Early cell phones were mainly installed in cars; handheld versions were as big as a brick, cost over a thousand dollars, and had a battery life measured in minutes. But in the 1990s the magic of the microchip drove prices down, shrank the phones to pocket size, reduced their energy needs, and packed them with computational powers. By the year 2000, 100 million people in the United States and a billion worldwide were using cell phones—not just talking on them but also playing games, getting information off the Internet, and using the keyboard to send short text messages, a favorite pastime of Japanese teenagers in particular. In countries where most households still lack a telephone— China and India, for example—the first and only phone for many people is likely to be wireless. Ultimately, Alexander Graham Bell's vision of a wired world may yield to a future in which, for everyone, personal communication is totally portable.
Alexander Graham Bell's invention of the telephone in 1876 rang in the era of talking at a distance. Innovators in the 20th century expanded the telephone's reach across continents and oceans, figuratively shrinking the world and connecting its citizens. Electronic switching systems and other technological advances helped customers place calls without the help of operators. By the year 2000, more than a billion people all over the world had gone wireless—using cellular technology to talk and deliver text and photos on super-lightweight telephones smaller than a deck of cards. Alexander Graham Bell's invention of the telephone in 1876 rang in the era of talking at a distance. Innovators in the 20th century expanded the telephone's reach across continents and oceans, figuratively shrinking the world and connecting its citizens. Electronic switching systems and other technological advances helped customers place calls without the help of operators. By the year 2000, more than a billion people all over the world had gone wireless—using cellular technology to talk and deliver text and photos on super-lightweight telephones smaller than a deck of cards. 1900 Telephone transmission extends across and between major cities As telephone transmission extends across and between major cities, "loading coils" or inductors are placed along the lines to reduce distortion and attenuation or the loss of a signal's power. Independently invented by the American Telephone and Telegraph Company's (AT&T) George Campbell and Michael Pupin of Columbia University, the loading coils are first used commercially in New York and Boston, nearly doubling the transmission distance of open lines. Pupin is awarded the patent for the device in 1904, and AT&T pays him for its use.1904 Fleming invents the vacuum diode British engineer Sir John Ambrose Fleming invents the two-electrode radio rectifier; or vacuum diode, which he calls an oscillation valve. Based on Edison's lightbulbs, the valve reliably detects radio waves. Transcontinental telephone service becomes possible with Lee De Forest's 1907 patent of the triode, or three-element vacuum tube, which electronically amplifies signals.
1915 First transcontinental telephone call Alexander Graham Bell makes the first transcontinental telephone call to Thomas Watson-from New York to San Francisco-after trials using De Forest’s triodes successfully boost the long-distance signal. What is the world’s longest telephone line consists of 2,500 tons of copper wire, 130,000 poles, three vacuum-tube repeaters, and countless numbers of loading coils. 1915 First transcontinental telephone call Alexander Graham Bell makes the first transcontinental telephone call to Thomas Watson-from New York to San Francisco-after trials using De Forest’s triodes successfully boost the long-distance signal. What is the world’s longest telephone line consists of 2,500 tons of copper wire, 130,000 poles, three vacuum-tube repeaters, and countless numbers of loading coils. 1919 Switching systems and rotary-dial telephones Bell System companies begin installing switching systems and rotary-dial telephones, though dial phones have been around since just before the turn of the century. The dial makes it easier for customers to place calls without an operator. The finger wheel of the dial interrupts the current in the phone line, creating pulses that correspond to the digits of the number being called. 1920 Frequency multiplexing concept AT&T develops the frequency multiplexing concept, in which frequencies of speech are shifted electronically among various frequency bands to allow several telephone calls at the same time. Metal coaxial cable eventually is used to carry a wide range of frequencies.
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