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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 -
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. -
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. -
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. -
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. -
First phone to combine a ringer and handset
AT&T introduces the Model 500 telephone, the first that combines a ringer and handset. The classic black rotary phone, featuring an adjustable volume control for the bell and later a variety of colors, becomes a cultural icon. -
First portable cell phone call is made
The first portable cell phone call is made by Martin Cooper of Motorola to his research rival at Bell Labs, Joel Engel. Although mobile phones had been used in cars since the mid-1940s, Cooper’s was the first one invented for truly portable use. He and his team are awarded a patent in 1975.