Early radio inventors used a variety of methods to detect radio waves. Those early detectors tended to be slow and cumbersome in operation and that limited transmission speed. In 1906, Lee de Forest built on the work of Thomas Edison and John Ambrose Fleming and invented an electron tube he called an “Audion.” His tube contained three internal elements: a filament, an electrode and a control grid. Today we call tubes of this type “triodes.” In 1907 De Forest received U.S. Patent #841,387 for his invention, one of the most important in the history of radio.
As inventors refined telephone equipment during the late 19th and through the 20th centuries, they introduced automatic switches that worked faster and could handle more calls than human operators. As they began introducing computerized switching equipment new advances in software proved necessary to make best use of the more capable technology. In 1971, Erma Hoover and Barry Eckhart received U.S. Patent 3,623,007 for a method of processing tasks in an electronic switching system. Their invention served to flexibly prioritize operations in the computer so that surges in the number of calls would not slow the telephone system. Hoover received her Ph.D. from Yale and ultimately became supervisor in the systems engineering department of Bell Labs. This three-part circuit board performed a “low-level logic” function in Western Electric’s model no. 1 Electronic Switching System.
Scientists and inventors in the 19th century recognized that some materials respond electrically to exposure to light. Alexander Graham Bell, for example, demonstrated in 1880 a “photophone” that could transmit voices using the action of sunlight on selenium. In the 1930s, Daryl Chapin studied magnetic recording at Bell Labs but later shifted to research on generating electricity with sunlight. In 1954, building on earlier work done by colleague Russell Ohl on fused silicon, Chapin, Calvin Fuller and Gerald Pearson invented a practical solar cell. In 1969 Chapin donated two of his experimental solar cells to the Smithsonian. He also donated a module used in a test installation in Americus, Georgia, to power a rural telephone relay.
This is the main section of Edwin Howard Armstrong's first regenerative radio circuit, constructed in late 1912 while he was a student at Columbia University. On top is a vacuum tube called an "Audion" made by Lee DeForest. Armstrong's research into the Audion's electrical properties led him to a fundamental discovery. He could wire the tube in such a way as to feed the weak received signal back into the circuit. This "regeneration" of the signal resulted in receivers that could detect distant signals and then amplify them so that they could be heard without headphones.
The invention of radio first involved the transmission and receipt of telegraph dots and dashes rather than voice, hence the term “wireless telegraphy.” The signals tended to be weak and required the operator to wear headphones to hear the signal. Edwin H. Armstrong invented a circuit that allowed people to hear distant radio transmissions without headphones. He built this device around a commercially-available DeForest “Audion” tube in 1913, while a student at Columbia University. The circuit also increased the sensitivity of the receiver and Armstrong received signals from Clifden, Ireland, San Francisco and Hawaii.
Scientists and inventors in the 19th century recognized that some materials respond electrically to exposure to light. Alexander Graham Bell, for example, demonstrated in 1880 a “photophone” that could transmit voices using the action of sunlight on selenium. In the 1930s, Daryl Chapin studied magnetic recording at Bell Labs but later shifted to research on generating electricity with sunlight. In 1954, building on earlier work done by colleague Russell Ohl on fused silicon, Chapin, Calvin Fuller and Gerald Pearson invented a practical solar cell. In 1969 Chapin donated two of his experimental solar cells to the Smithsonian. He also donated a module used in a test installation in Americus, Georgia, to power a rural telephone relay.
Scientists and inventors in the 19th century recognized that some materials respond electrically to exposure to light. Alexander Graham Bell, for example, demonstrated in 1880 a “photophone” that could transmit voices using the action of sunlight on selenium. In the 1930s, Daryl Chapin studied magnetic recording at Bell Labs but later shifted to research on generating electricity with sunlight. In 1954, building on earlier work done by colleague Russell Ohl on fused silicon, Chapin, Calvin Fuller and Gerald Pearson invented a practical solar cell. In 1969 Chapin donated two of his experimental solar cells to the Smithsonian. He also donated a module used in a test installation in Americus, Georgia, to power a rural telephone relay.
Until the late 20th century telephones, computers and televisions operated in largely separate realms. Sometimes those realms intersected, as when computers or television signals were transmitted over telephone wires, but users generally operated separate, highly specialized devices for each. In the 1990s, however, these realms began to converge. This prototype PDQ-1900 smartphone shows the convergence of telephone and computer technologies in one unit. Cellular telephones entered the market in the 1980s and by late ‘90s many Americans owned one. At the same time small, handheld computers called personal digital assistants were also introduced by several makers. Palm Inc. made one popular line of PDAs and in 1999 Qualcomm combined the functions of a Palm PDA with a cell phone in this PDQ-1900 into a device that came to be known as a “smartphone.” Later, more powerful smartphones added a vast array of features–including the capability of receiving television programs erasing the lines that used to exist between these separate technologies.
Ray Dolby’s 1965 invention of a system for reducing unwanted noise in magnetic tape recording significantly enhanced sound quality in consumer devices. His circuit design compressed and then expanded the electrical signal, a design he called a “sound compander” for which he received U.S. Patent 3,846,719. At first, Dolby’s compander was sold as an add-on component but by the early 1970s, it became an integral part of the equipment. This Advent model 201 cassette deck features a switch to activate Dolby’s system. The recorder also included a switch that allowed the use of chromium oxide tapes. The CrO2 tapes gave superior performance than ordinary ferrite oxide tapes but the sound properties could change over time. The switch helped the Dolby system compensate.