The Radio Corporation of America, in 1989, produced a series of advertisements proclaiming that year as “The Fiftieth Anniversary of Television”. It apparently wished the general public to believe that television, or perhaps television broadcasting, began with RCA’s first forays into the medium. While that is partially true, there’s much more to the story than that. As Paul Harvey might have remarked, here is “the rest of the story”.
The story begins roughly in 1884 with a German engineering student named Paul Nipkow, who had an idea for a device he called an “electric telescope”. Nipkow reasoned that the action of the human eye, which takes in an image all at once, most likely could not be duplicated by mechanical means. He further reasoned that the image would have to be broken up into small parts which could then be transmitted, perhaps over telegraph lines. At the receiving end, if the image’s small parts were presented quickly enough, the action of the eye (through persistence of vision) would then come into play and reassemble the image.
Nipkow hit upon the concept of a scanning disk to accomplish that purpose. Imagine a disk, of roughly 15 to 24 inches in diameter, with a spiral of small holes drilled in it. The first hole is placed at the very top of the disk near the outer edge, and the holes continue on around the disk in a descending spiral, with about an inch or so separating each hole from the next. In a typical disk, there would be 36 or 48 such holes. The disk is mounted on the shaft of a motor, and rotated at a very fast speed. The subject to be televised could thus be scanned, and the image parts reassembled (with a similar disk) at the receiving end to reproduce the image.
Such was Nipkow’s idea, which he later patented. However, it remained only an idea for many years. Nipkow never built such a device, as far as is known, and it would fall to later experimenters to find a practical use for his scanning disk arrangement.
EARLY EXPERIMENTS IN MECHANICAL TELEVISION
The action now shifts to the 1920s. The advent of motion pictures and radio naturally caused some experimenters to begin thinking about combining the two and transmitting sight along with sound. Nipkow’s scanning disk was dusted off and given a second look by some of those experimenters. One of the most successful was John Logie Baird of Scotland.
Baird approached the problem in terms of a total system: a transmitting setup, a means of transmission, and a receiving setup. In his early experiments, he attached a scanning disk to an electric motor. A powerful light shone upon the disk, producing a “flying spot” of light as the disk spun, which would then scan the subject. The spot of light bounced off the subject and was detected by a photocell, which converted the light variations to electric impulses. In some experiments, the light was trained upon the subject. The scanning disk was instead mounted in front of the photocell, and scanned its electrode to produce the impulses.
Those electric impulses were fed into a vacuum tube amplifier and sent, over a closed wired circuit, to the receiving apparatus. This consisted of another disk and motor, rotating at roughly the same speed as the transmitting disk. Behind this disk was a light source, connected to the output from the transmitting line. Baird quickly found that he had to use a neon lamp, as a regular incandescent lamp’s filament could not follow quickly enough the variations of the electric impulses from the transmitting setup. The neon lamp contained a small square screen, and the lighting of this screen varied in accordance with the impulses from the transmitter. The receiving disk would scan the lamp’s screen, and thus the image would be reproduced.
One thing that might occur to anyone regarding this entire setup is the problem of synchronization between the transmitting disk and the receiving disk. As the first hole on the transmitting disk scanned the subject, it was necessary that the corresponding hole on the receiving disk (as it scanned the receiving lamp) be in the same spatial position as the transmitting disk. Any mismatch in synchronization produced framing errors in the received image (in later electronic television sets, this would be analogous to problems with the vertical or horizontal hold).
A number of schemes were developed to maintain synchronization. The simplest of them was to provide, on the receiving set, a control to vary the speed of the scanning disk motor. One could then speed up or slow down the receiving disk and bring it into sync with the transmitting disk. This system was later refined by the use of a synchronization signal transmitted along with the picture signal.
In America, similar experiments were conducted by C. F. Jenkins. Though he duplicated some of Baird’s early experiments, Jenkins was more interested in a system to transmit movies. He used a scanning disk made up of lenses, and was able to demonstrate a working system by 1925. Jenkins began transmitting his “radiomovies” in 1928, and formed a company to market receiver kits designed to pick up the transmissions.
By 1927, Baird’s system worked well enough that he was able to demonstrate practical television to a committee of scientists in England. The demonstrations were successful and led to the formation of the Baird Television Developmental Company. The received images were still crude – barely larger than a business card. Nonetheless, Baird kept refining the system, chiefly in improvements to the scanning methods. He was even able to demonstrate a rudimentary form of color television, using a disk with three spirals of holes. His color receiver used, in addition to a neon lamp for the red color, a mercury vapor lamp for blue and green.
In 1929, Baird began talks with the British Broadcasting Corporation after more successful demonstrations. The BBC’s engineers solved one of his last lingering problems – that of transmitting sight and sound simultaneously. He entered into an agreement with the BBC to begin a series of experimental transmissions in 1930. As part of the agreement, Baird’s company began producing commercially available receiving sets, known as “Baird Televisors”.
Though Baird’s television system worked well enough that the BBC scheduled regular television broadcasts –even presenting live dramas – his system was facing sudden obsolescence. The American experimenters had not been idle, and they believed that the future of television lay with all-electronic means of transmission and reception. While Baird had concentrated on mechanical systems, Vladimir Zworykin of the Westinghouse Company, and Philo T. Farnsworth, an independent inventor, had concentrated on purely electronic systems. Their inventions would put an end to any further development of mechanical television.
Loomis, Mary Texanna. Radio Operating and Theory. Washington, DC: Loomis Publishing Company, 1930.
Tiltman, Ronald F. Television in Natural Colors Demonstrated. Radio News, October 1928.
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