Voip Blog
Video Transmission In 1927
Wednesday, May 14, 2008
The Bell System was doing a lot more than telephones. That's part of the reason they experienced anti-trust and breakup orders twice in its history, once in 1956 and again in 1984 when the Bell System was effectively broken up and declared dead.
One thing they were doing in the 1920s was experiments with transmitting video. This is before the television was invented, so they had to come up with ways of both capturing and transmitting a video image--synchronized with audio. Not a particularly easy feat in those days, given the available technology.
At the end of the day, the folks at Bell Labs had to convert the video and audio into electrical impulses, transmit them some distance--between Washington D.C. and New York, in the initial demonstration--and reconstruct it and display it on the other end.
The system devices by Bell Labs was electro-mechanical in nature. Specifically, it was a spinning disc with 50 small holes arranged in a spiral. This served to focus a bright light source into a narrow beam and scan the subject 16 times per second. A photoelectric cell received the light reflected off the subject and converted the light into electrical signals, which were then sent over the wire to their destination.
At the receiving end, the electrical signals went to a neon globe tube, which produced a light that changed rapidly with the fluctuation of the electrical impulses. A rapidly spinning disc similar to that used on the sending end was placed between the tube and the viewer. The disc on the receiving end focused a narrow beam to a succession of points 16 times a second.
In order for the sender and receiver to be synchronized, the video was transmitted over one line, a synchronization signal was sent over a second line, and the audio portion was on a third.
The result? A grainy, black-and-white 50-line image about 2 inches by 2.5 inches shown at 16 frames per second. To put that in perspective, standard definition television is 525 lines of resolution shown at 30 frames per second. High definition is either 720 lines of resolution or 1080 lines of resolution, depending on which mode the program is being displayed in.
The initial demonstration in 1927 was one way. By 1929, they had figured out how to transmit video in color. By 1930, there was two-way video phone service between AT&T and Bell Labs respective headquarters.
These days, transmitting video is a lot easier. Heck, you can do it using your mobile phone, complete with live streaming. Two-way video communication can happen much easier--and with much less equipment--than it required in 1927. And you only need one line to do it--your Internet connection.
