Fred Hammond, VE3HC, is a veteran Radio Ham who has been on the air since 1929. During the early 1930’s, he was one of a handful of radio experimenters in Canada to become interested in mechanical television, building his own mechanical kit vision receiver. As an active Radio Ham, he was able to audibly monitor the various mechanical television signals.
Always a sensation, television was hardly an overnight success. In 1926, New York Times radio editor Orrin Dunlap called the new medium “an inventor’s will-o’- the-wisp.”
A year earlier, a Scot, John Logie Baird, and an American, Charles Francis Jenkins, generated the first live pictures by pairing (or synchronizing) primitive mechanical scanning discs at transmitter and receiver ends. These demonstrations, soon conducted at department stores, trade fairs, and before invited audiences of scientists and government officials, attracted the curiosity of press and public. Especially interested were some of the quarter- million amateur “wireless” operators, whose numbers grew during the early 1920s, when “radio mania” swept North America. These hobbyists were among the original producers and consumers of both radio and television.
In 1928, Jenkins began irregular broadcasts of the crude silhouettes he called radiomovies. He described the thrill for his amateur audience as they “fished” for his signals on homebuilt contraptions: “thousands of amateurs fascinatingly watch the pantomime picture in their receiver sets as dainty little Jans Marie performs tricks with her bouncing ball, Miss Constance hangs up her doll wash in a drying wind, and diminutive Jacqueline does athletic dances with her clever partner, Master Fremont.”
At its inception, radio “listening-in” was an active, mainly male pastime, requiring technical know-how, and constant adjustments to the set.
“Lookers-in” to early mechanical television patiently fished for signals. Sometimes they caught tiny, indistinct images. A separate radio set could be used to tune in sound with the picture. Radio entered most households only after it was domesticated. This meant that it came to resemble furniture instead of a gadget, became easier to operate, and could be enjoyed by more than one person at a time. Television followed a similar route into the home, but its complex and expensive assemblage dictated a lengthier experimental period before costs came down, and before the invention of larger screens and clearer pictures could domesticate “seeing at a distance.”
Despite these early limitations, the pioneers of crude mechanical television demonstrated basic principles of picture scanning and synchronization of transmission and reception. They also glimpsed the medium’s potential for storytelling. In 1928, the first live drama broadcast, a three-camera production called “The Queen’s Messenger,” was received on a General Electric Octagon set in Schenectady, New York. In 1931, the Radio Corporation of America (RCA) broadcast experimental signals from the Empire State Building, featuring a familiar cartoon character, Felix the Cat. The first TV star was born. By 1935, mechanical television had reached a dead end in North America. Image resolution remained low, at best reaching 120 lines of picture definition. Transmission and reception standards were nonexistent. Available programming was unpredictably scheduled. Lacking an audience, advertisers were reluctant to purchase commercial time.
One of the earliest proposals for a mechanical television system was put forward by German researcher Paul Nipkow in 1883. When he developed patent No. 30,105, he was an unknown twenty-three-year-old student living in Berlin.
It proved to be the basis for most early television schemes in the world, although he never built the apparatus. In Nipkow’s patent, which he called an ‘electric telescope,’ a disc was punched with holes in a spiral near the outer edge. When the disc revolved, each hole vertically scanned a line of the image, allowing variations in light to reach a selenium cell. As one hole swept over a segment of the picture, the next in sequence tackled the portion next to it, until the complete subject had been scanned. The selenium cell transferred the light variations to an electronic signal. Pictures were reconstituted at the receiver by a similar disc which was synchronized with the transmitter. Jenkins One of the better known experimenters with mechanical television was Charles Francis Jenkins, a prolific American inventor.
In May 1920, at the Toronto meeting of the Society of Motion Picture Engineers, Jenkins introduced his “prismatic rings” as a device to replace the shutter on a film projector. This invention laid the foundation for his first radiovision broadcast. He claimed to have transmitted the earliest moving silhouette images on June 14, 1923, but his first public demonstration of these did not take place until June of 1925.
Jenkins Laboratories constructed a radiovision transmitter, W3XK, in Washington D.C. The short-wave station began transmitting radiomovies across the Eastern U.S. on a regular basis by July 2, 1928.
Jenkins wrote in 1929: “This gave the amateur action-pictures to ‘fish’ for; and during August following a hundred or more had finished their receivers and were dependably getting our broadcast pictures, and reporting thereon, to our great help.” It was in this way that Jenkins actively promoted enthusiasm and experimentation in the short-wave radio community, and the U.S. experienced its first television boom, with an estimated 20,000 lookers-in.
Baird John Logie Baird, a Scottish engineer and entrepreneur, achieved his first transmissions of simple face shapes in 1924 using mechanical television. On March 25, 1925, Baird held his first public demonstration of “television” at the London department store Selfridges on Oxford Street in London. In this demonstration, he had not yet obtained adequate half-tones in the moving pictures, and only silhouettes were visible. In the first week of October, 1925, Baird obtained the first actual television picture in his laboratory. At this time, his test subject was a ventriloquist’s dummy, “Stooky Bill,” which was placed in front of the camera apparatus.
Baird later recollected, “The image of the dummy’s head formed itself on the screen with what appeared to me an almost unbelievable clarity. I had got it! I could scarcely believe my eyes and felt myself shaking with excitement.” After much discussion with his business associates, and further improvements, Baird decided to publicly demonstrate television on Tuesday 26 January, 1926, again at Selfridge’s department store. This was the first opportunity for the general public to see television.
The Baird company continued to publicize this historic demonstration, and J. L. Baird’s other scientific breakthroughs as they feverishly worked to obtain financial backing and construct a line of home receivers. With Baird’s transmitting equipment, the British Broadcasting Corporation began regular experimental television broadcasts on September 30, 1929. By the following year, most of Britain’s major radio dealers were selling Baird kits and ready-made receivers through retail and by mail order.
The Baird company was licensed to provide intermittent broadcasts from the BBC transmitters, and at least 3,000 enthusiasts “looked in” to see as well as hear some of Britain’s most popular singers and comedians.
Mechanical TV: How it works
The scanning and reproducing discs are similar. Both are mounted on driving motors, and each is punched with a spiral of small holes along the outer edge. The number of holes matches the number of lines of picture definition. At the transmitter in this mechanical system, the studio is in total darkness. A light emanates from a lamp behind the disc and, projected through the holes set in the spiral on the outer edge, scans the features of the subject’s face. The photocell converts these variations in the reflected light into the electric impulses, which, once amplified, can be transmitted by radio waves. At the receiver, the signal is converted into a sequence of bright flashes by the neon tube. The reproducing disc rotates rapidly in front of this tube, and converts each flash of the lamp into a small element of the image. The rapid speed of the disc makes “persistence of vision” possible for the looker-in.
“Persistence of vision” means that the brain retains an image for one tenth of a second after it is perceived by the eye. The
rapid repetition of moving images (in film or television) tricks the brain into perceiving continuous images.
The General Electric Octagon, 1928 (U.S.A.) with RCA radio 1928 (U.S.A.) This mechanical television receiver was built for a 48- line television system developed during 1927 by Ernst W. Alexanderson, who was the Chief Consulting Engineer at the GE laboratories in Schenectady, New York. An elaborate experimental transmission on this type of receiver was internationally recognized as the first television drama. Entitled “The Queen’s Messenger”, the play had two characters, with only the heads or the hands of the four actors visible at any one time. Two actors spoke the lines, while the other two acted as “hand models”. The transmitted signal was received on a console radio and monitored through the 3” lens on the Octagon by the director, and the actors were only a few feet away. GE considered mass-production of the Octagons, but this never materialized.
Daven Tri-Standard Scanning Disc, 1928 (U.S.A.) The lack of a common standard of picture definition contributed to the demise of the mechanical television boom of the late 1920’s and early 1930’s. One solution was to make a television set that could receive a number of different standards. This Daven unit was based on a large 24” disc capable of scanning three different standards of picture definition, 24-line, 36-line and 48-line, enabling the viewer to receive more stations. The television signal was received by a short-wave radio. The operator then had to adjust the height of the neon lamp to match the correct spiral of holes, and synchronize the rotation of the scanning disc to the corresponding rotations per minute. The tiny picture would be visible in one of the three frames (marked within the black outline).
Homebrew W1IM Scanning Disc, 1928 (U.S.A.) This home-made scanning disc television unit was built by the Connecticut radio experimenter, Clifford Fraser, using hand-written instructions sent to him by the mechanical television pioneer and broadcaster, Charles Jenkins. Jenkins was aware that “Radiovision” was in its infancy and actively encouraged involvement, experimentation and the exchange of information within the amateur radio community. In the late 1920’s, he even went so far as to offer Radiovisor Kits similar to this one at $7.50 U.S. postage paid - a price so low that it meant a loss for his company.
Jenkins Model 202 Radiovisor, 1929 (U.S.A.) This mechanical scanning-drum unit was engineered, designed and manufactured by the Jenkins Television Corporation, a company founded in 1928 by the American television pioneer, Charles Francis Jenkins. As early as 1894, he presented an article in the periodical, Electrical Engineer, on a method of electrically transmitting pictures. He was one of the earliest to succeed at television transmission, and claimed to have executed the first reported transmission of television by radio in 1923. Hugo Gernsback of Radio News and Watson Davis of Popular Radio witnessed a demonstration in the same year. In 1928 Jenkins announced the birth of a new entertainment industry, “Radio Movies”. Shortly thereafter, Jenkins Laboratories Incorporated initiated 48-line silhouette broadcasting through regularly scheduled telecasts over station W3XK and a few other stations that showed “Radio Movies”. Jenkins preferred the term “Radiovision” to “Television”, which explains this unit’s name.
Baird Televisor, 1930 (U.S.A.) The Plessey model was the most popular version of the mechanical “Televisor” to be available to the British and West European retail buying public. It was engineered and designed by John Logie Baird and manufactured by the Plessey company in England. It was purchased by television enthusiasts to watch the periodic Baird Studios/BBC broadcasts available from 1929 to 1932. The 30 line images did not take up the entire “screen,” but were in fact 6cm high and 2cm wide. Instead of black and white, they were black and red due to the colour of the neon gas in the lamp. About 1,000 of these sets were originally produced and priced at just over 18 British pounds each. There were kit receivers without the tin cabinet, available from Baird’s for only 7 pounds. Baird was one of the true pioneers of television. He successfully demonstrated the possibilities of the Nipkow system of mechanical television by achieving the first television picture in October, 1925.
Western Television Corporation Visionette, 1932 (U.S.A.) Western Television Corporation played a significant role in the evolution of television in North America. Canada’s first experimental television station, which was operated by the Montreal newspaper La Presse and radio station CKAC, was supplied with Western Television equipment. The Canadian public witnessed Western Television’s technology through a special mechanical projection apparatus, which was demonstrated at Eaton’s and department stores in Toronto, Montreal and Winnipeg during 1933. In the U.S., Western’s travelling demonstrations included a 9-day run at Macy’s in New York that was witnessed by over 200,000 people. The Western Television Corporation drew on the talents of television pioneer Ulysses A. Sanabria, who is known for his use of interlaced scanning. Interlacing improved picture quality by reducing flicker. This television utilizes an interlaced aluminum scanning wheel and 3” magnifying lens. It was among the last and most advanced mechanical home televisions to be in use before the electronic sets began to show greater promise.
Source: These are excerpts from the catalog from the exhibition at the Royal Ontario Museum, Watching TV. The exhibition runs through September 15, 1996.
Baird Mechanical Television, Part One: Technical Introduction
From Trevor Blake
The discovery leading to the possibility of mechanical television was an accident. While laying the first trans- Atlantic cable, a worker noticed that some of his tools were glowing. An analysis of the metal revealed a concentration of selenium, the metal used soon after in the earliest photoelectric cells. Selford Bidwell used a photoelectric cell to transmit an image electronically in 1881: over the course of several minutes, a two-inch square image could be sent via telegraph lines.
Three years later, Paul Nipkow was granted a German patent for the Nipkow disk a complete and functional television system in 1884.
The development of the neon tube in 1910 furthered mechanical television. Film achieves the illusion of motion by taking advantage of the persistence of vision: still images in a fixed location which are refreshed at a rate of sixteen times per second (or more) are interpreted by the human mind as moving images. Television achieves the illusion of motion in a similar but unique fashion. Rather than refresh the entire image at once, as film does with each cell that passes in front of the projector’s light, television refreshes an image one line at a time in a scanning process.
Within the cathode ray tube, an electron gun scans a single line of an image from one side to the other, then scans the line underneath it, until it has scanned an entire image.
The Nipkow disk is an earlier, mechanical means of achieving the same side-to-side, top-to-bottom scan process. It consists of a disk that rotates on its axis. A series of evenly spaced, uniformly sized holes are cut into the disk, spiraling in toward the center. The disk is housed in a box with a small viewing window: the outermost hole of the disk will form the outermost scan line visible in the viewing window, and each additional hole will form additional scan lines. The rotation of the disk as seen through the viewing window provides scanning from side to side, and the spiral placement of the holes provides scanning from outermost to innermost scan line. A light source which can be varied in intensity is placed on the opposite side of the disk behind the viewing window. As the light flickers and the disk rotates, television is achieved.
Mechanical television cameras and receivers alike use the Nipkow disk, but where the receiver uses a flickering light to produce an image, the camera uses a photosensitive cell to generate an image. The rotation of the disks is synchronized by part of the transmission signal (which has included radio, short wave and telephone) or direct wiring.
The disks rotate at around 900 rpm and initially produced television two inches square. The earliest mechanical televisions offered between 16 and 24 lines of resolution. By the late 1920s, they offered between 48 and 60 lines. Double and
triple spirals of scanning holes were used, as well as scanning drums and belts. Lenses were fixed in the scan holes to project the image onto a larger screen (up to 8 inches in some cases).
Mechanical television cameras were synchronized with film projectors, allowing the transmission of film. Studio B of the BBC used a hybrid of this system: the subject was filmed, the film was instantly processed and then scanned for transmission. There was a delay of around one minute between event and transmission as the film developed.
The light required for mechanical television is intense, so much so it was nearly impossible to perform while being televised. The flying spot camera was one solution to this problem: an additional scanning disk, synchronized to the camera, cast a brilliant light on the subject in the same spot they were being scanned.
The rest of the studio, including the control room, was kept in complete darkness. Another solution to this problem was the use of multiple arrays of concave lenses to focus light into the camera more efficiently.
Source: BOOKSManly, Harold: DRAKE’S RADIO ENCYCLOPEDIA (Drank & Co. 1927) Ghirardi, Alfred: RADIO PHYSICS COURSE (Radio & Technical Pub. 1933) Zworkin, Y. K. and Morton, G. A.: TELEVISION (John Wiley 1940) Goldstein, Norm: THE HISTORY OF TELEVISON (Portland House 1991) Kisseloff, Jeff: THE BOX (Viking 1995) Ritchie, Michael: PLEASE STAND BY (Overlook Press 1994) Winship, Michael: TELEVISION (Random House 1988) Yanczer, Peter: THE MECHANICS OF TELEVISON (Peter Yanczer 1987) (Peter Yanczer, 835 Bricken Pl., St. Louis MO 63122 USA) MAGAZINES Popular Science, March 1932 Mechanics and Handicraft, Vol. 1 #1, Winter 1933 Television: Journal of the Royal Television Society, April 1995 VIDEO The Race for Television, BBC
Baird Mechanical Television, Part Two: Technical Introduction
The Dead Media Notebook Page 21