© Mark Ollig
The 1920s saw a surge of research and development in television technology.
Two different approaches emerged: mechanical and electronic.
The mechanical television system used a Nipkow disk, a spinning platter with holes that scanned the moving images line by line and transmitted them as electrical signals over wire or radio waves.
German engineer Paul G. Nipkow (1860 to 1940) envisioned an “electric telescope” and invented the Nipkow disk in 1884.
Its principle of sequential scanning remains fundamental to modern television technology.
In the early 1920s, American Telephone & Telegraph (AT&T) engineers worked on the mechanical television system at the Bell Telephone Laboratories in New York.
Under the leadership of Herbert E. Ives (1882 to 1953) and Frank Gray (1887 to 1969), the team at Bell Labs, consisting of engineers, scientists, and technicians, made significant contributions to the long-distance transmission of television.
Their work involved a mechanical scanning system that featured a Nipkow disk with a spiral pattern of holes, which was essential in the sequential scanning of images for transmission as electrical signals.
It featured several small holes, which allowed light to pass through and illuminate the subject.
The light intensity varied according to the scene’s characteristics, such as its brightness level.
These variations were captured by a photocell, which then converted the light patterns into electrical signals modulated for transmission via wires or radio waves to a corresponding receiver.
At the receiver’s end, another synchronized Nipkow disk, paired with a neon lamp, decoded the signals.
In conjunction with the rotating disk, the lamp’s varying brightness recreated the original scene as a visual image on a screen.
The resulting image boasted a resolution of 185 lines and a frame rate of 16 frames per second, which, while low by modern standards, marked a significant achievement for the time, rendering moving images recognizable.
Vladimir Zworykin’s (1888 to 1982) invention of the iconoscope in 1923 represented a leap forward in television technology.
This device, nearly six inches long and 3.75 inches across, featured an array of 50,000 photoelectric cells laid out in a spiral pattern.
These cells captured the image and transformed it into an electrical signal, functioning as an “electric eye.”
The iconoscope was a device that generated a video signal, which was then displayed on a cathode ray tube.
Despite its limited resolution of 24 lines and a refresh rate of 12 frames per second, the iconoscope was a significant breakthrough in developing electronic television systems.
It is widely regarded as the predecessor to the modern video camera tube, analogous to early television cameras, and represented a significant advancement from earlier mechanical designs.
In 1927, the technology for television was still in its early stages.
The quality of the TV image depended on the number of scanning lines and frame rate – the more scanning lines and frames per second, the more precise and detailed the picture.
A rectangular iconoscope screen measuring two inches by 2.5 inches was used to see the person on the other end.
At 2 p.m. EST, April 7, 1927, AT&T began publicly demonstrating its television system at the AT&T auditorium on 463 West Street in New York City, where reporters, journalists, researchers, and scientists had assembled.
Their television system transmitted its signals over 220 miles of copper telephone lines from Washington, DC, to New York.
In 1927, the telephone lines could not handle high-frequency television signals, as they were engineered to handle voice communications, which operate within a much lower frequency range than video signals.
AT&T installed special equipment and components to send TV signals via phone lines between Washington, DC, and New York City.
The equipment included amplifiers, load coils, equalizers, and components to counteract distortion and maintain signal quality.
During AT&T’s portion of the wireless demonstration, a radio frequency of 2.5 MHz was used due to its long-distance transmission capabilities.
This frequency carried the television video signal and was broadcast from AT&T’s experimental radio station 3XN in Whippany, NJ, which had a 50-foot antenna tower and a 500-watt transmitter.
Attendees at the AT&T auditorium could speak with, hear, and see US Secretary of Commerce Herbert Hoover (1874 to 1964) in real-time from Washington, DC, on the telephone, loudspeaker, and large screen set up on the stage.
Herbert Hoover was the first to appear on live television in the US; he would become the 31st president in 1929.
A woman singing was televised live over the 2.5 MHz radio frequency during the demonstration.
AT&T’s President Walter S. Gifford (1885 to 1966) then spoke with and saw Hoover in a real-time televised broadcast.
The Minneapolis Daily Star newspaper reported April 8, 1927, that Gifford sat before “the television apparatus and began conversing with Mr. Hoover. As the telephone company president talked, he looked through a rectangular aperture about two inches by two and one-half inches and could see and hear Secretary Hoover.”
The California Visalia Daily Times newspaper called it a “Telephone with Eyes.” April 30, 1927.
I learned AT&T used its television technology to improve the transmission capacity of its long-distance telephone network.
The April 7, 1927, television demonstration was filmed, and a one-minute segment can be seen at http://tinyurl.com/TVHoover.
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| A diagram showing the schematic of the April 7, 1927, television demonstration over radio and telephone circuits. |
