A CDE Definition
The technology used in the first TV systems. See video/TV history.
Before totally electronic TV cameras and receivers were built, electromechanical "scanning disc" systems produced the first TV images. As far back as 1884, German inventor Paul Nipkow designed such a system. Using a rotating disk with a spiral pattern of holes, light from the subject came through the holes and reached a selenium photocell, thereby breaking up the image into pixels. Each rotation produced one TV frame. Photosensors detected the brightness of each pixel similar to the way electronic cameras work today, and the light was turned into a modulated electronic signal.
The signal was transmitted to and synchronized with the receiver's rotating disk, which had the same spiral pattern. The signal modulated a neon lamp that beamed through the disk's holes to a magnifying lens which the viewer looked into.
The First TV Station
In the 1920s, scanning disc systems were being developed at Bell Labs and General Electric, as well as by John Logie Baird in London and Charles Jenkins in Baltimore.
In 1928, using his "Radiovision" system, Jenkins is credited with starting the first TV station in the U.S. in Wheaton, MD. Using proprietary systems with receivers mostly sold in kit form, mechanical disc TV was transmitted from approximately 20 stations. The broadcasting was limited, and the audience was even more limited. Images were blurry, and the tuning knob had to be constantly adjusted; nevertheless, these systems were considered modern miracles.
The Scanning Disc Was Finished
By 1935, most people had given up the ghost. It had become very apparent that the mechanical system would never become commercial. Synchronizing the discs and modulating light sources at the higher speeds necessary to make an image acceptable were impossible to achieve.
All Electronic - Zworykin and Farnsworth
Throughout the 1920s, RCA's Vladimir Zworykin was busy developing the Iconoscope camera tube that would become the foundation for the all-electronic systems that would follow. Zworykin's work was based on a CRT receiver invented by his instructor at St. Petersburg Institute of Technology in Russia in 1907.
At the same time, Philo Farnsworth was developing an electronic TV system, which he patented and demonstrated in 1927. Farnsworth's patent was approved in 1930, but Zworykin's 1923 patent would not be approved until 1938 because so many revisions were made. For a brief time, Farnsworth and Zworykin were racing to perfect their technologies with just a river between them: Farnsworth in alliance with Philco in Philadelphia and Zworykin at RCA in Camden, NJ, directly across the Delaware River.
RCA Paid Farnsworth
Although Sarnoff had a single goal of controlling TV as it had radio, it was proven that Zworykin's system infringed on some of Farnsworth's patents. RCA reluctantly paid Farnsworth's company royalties until the patents ran out. But years of delay tactics had taken their toll. By the late 1940s, the last of Farnsworth's company was sold to International Telephone and Telegraph (ITT), and Farnsworth went to work for ITT as a scientist, devoting most of his remaining life to nuclear fusion.
RCA Was Convincing
Radio Corporation of America was the most powerful electronics company in the 1930s. Its PR machine was huge, and nobody would forget its spectacular demonstration of TV at the 1939 World's Fair. Citing Zworykin's 1923 patent application and coating everything with RCA-colored glasses, it succeeded in making everyone believe that RCA, Sarnoff and Zworykin were the sole creators of electronic television. In 1939, NBC began to broadcast TV using the RCA system, and two years later, NTSC was approved. In 1941, the U.S. finally had a national, electronic TV standard, which endured until 2009 (see DTV). See NTSC and video.
The Scanning Disc
Before/After Your Search Term
|scan head||SCART connector|
|scan line||scatter diagram|
|scan rate||scatter plot|
|scan technology||scatter read|
|scanning device||SCELBI 8H|
Terms By Topic
Click any of the following categories for a list of fundamental terms.