The Beginning of Television
It is very strange to imagine for today’s media savvy population that there was once a world without smart phones or computer monitors displaying colorful photographs in all their detail, or without flat screen TVs that show high definition broadcasts from thousands of miles away, or enormous movie theater screens that present digitally recorded images as real as a stage show.
But just 100 years ago, in 1918, nothing like that existed; although electric transmission of sound through wire, called the “telephone” was commonplace, wireless telephony was just in the beginning stages, becoming “radio” for everyone to enjoy around 1920. This was owed to the development of the vacuum tube as an electronic amplifier and an all-around versatile tool for many auxiliary tasks in the electronic world.
Nevertheless, inventors, and to their credit, also science fiction writers, had much larger dreams than just sound transmission, and they envisioned, at that time already, a modern world with electronic instruments providing instant high quality optical image pickup, long distance transmission and display; just the means to fulfill these dreams were not available yet. Step by step, however, the highly complicated technical problems associated with these dreams of “television”, which translates to seeing an image from afar, started to be tackled by very talented people.
The first problem to be solved was how to pick up, transmit and display an image. Our eyes can show us how an optical image can be analyzed in a biological system and transmitted into the brain for us to be seen. The eye has millions of little photo-receptors that cut the image to be viewed into millions of tiny dots, with their brightness value being transcoded into an electrical signal that is sent via a tiny nerve strand into the optical reception area of the brain. There, millions of simultaneously transmitted electrical impulses over millions of nerve fibers from millions of photo-receptors are assembled into one continuous image.
Theoretically, this system could be directly replicated by electronic means. Thousands (already scaled down from millions) of photoelectric elements could be connected through thousands of wires, through thousands of amplifiers to thousands of electric lamps, each lamp displaying the exact brightness of the image dot picked up by the photoelectric element. Standing far enough away from such a “lamp screen” as not to make out the individual lamps but just seeing one uniformly illuminated screen, an observer could watch a whole image assembling out of the individual image dots.
One can see immediately that the “electronic eye” would be quite impractical, due to the thousands of wires, lamps and pick-up cells required. Telephony only requires one wire (and the ground for the return current) to transmit sound, so how could we possibly send the thousands of little image dots through one wire? This could be accomplished by “scanning” the image, dot by dot, and sending the dot brightness signals sequentially, one after the other. If this is done fast enough, an image with thousands of image dots can be assembled in a fraction of a second; the eye of the observer would not be fast enough to see the individual scanned image dots, rather, a full image with all dots being perceived simultaneously would appear in the eye, due to a phenomenon called “persistence of vision”.
The concept of scanning a picture through mechanical means was first proposed by Alexander Bain in 1843. A mechanical scanning disk driven by a motor, which became the basis of television in the early years, therefore called “mechanical TV”, was proposed in 1884 by Paul Nipkow. Such a scanning disk has holes in it, which are placed in a spiral around the disk, each hole slightly lower than the other. If seen through an aperture on top of the disk, framing the picture to be scanned, each hole traces an arc over the image, scanning the whole image with one arc after another from top to bottom; after a full disk rotation, the first and highest hole appears again, to repeat the scanning cycle.
To construct a camera, called a “spotlight scanner”, with such a scanning disk that could pick up the face of a person in a dark room, a very bright light is placed behind the disk. The disk is turned by a motor, so that it makes one revolution every frame of the TV picture. In a very popular mechanical television standard used for many years, the disk has 30 holes and is rotated 12.5 times per second. A lens in front of the disk focuses the light on the subject being televised.
As the moving spot of light coming from the disk hits the face of the subject, it is being reflected from the subject, brighter or darker, dependent on the contours and area brightness of the face. The reflected light is picked up by a photoelectric cell, which converts light into an electric current. Dark areas of the face reflect little light, and only a small amount of electric current is produced, while bright areas reflect more light, and therefore more electric current is produced.
The electric current coming from the photocell, which is also called the video signal, varies continuously in intensity; this varying electric current is highly amplified and transmitted over wire or over the air to a receiver, which also has a scanning disk turned by a motor in exact synchronism to the camera disk (a difficult task to achieve, however, several synchronizing methods were developed and successfully applied). A radio receiver or amplifier picks up the video signal and feeds it to a lamp placed behind the disk that faithfully converts the changing electric signal into changing amounts of light. In early receivers this was a neon lamp, the only lamp at that time that could translate the fast current changes into equally fast light changes. For dark areas, little light is emitted, for bright areas, more light is emitted. The image is viewed on the other side of the disk, usually through a magnifying lens.
Here is an illustration of a television system that could be built using such a Nipkow disk:
In 1884 however, when Paul Nipkow filed his scanning disk patent, vacuum tubes and photoelectric cells needed to construct a working television system did not exist. Therfore, Paul Nipkow’s invention and associated patent were not utilized until about 40 years later.
The first mechanical television system that produced real television images was developed by the Scottish inventor John Logie Baird and displayed successfully in 1923. Additional attempts in picking up, transmitting and receiving television images were made in the US by Charles Francis Jenkins in the mid 1920s.
The intial image resolutions that could be transmitted using Nipkow disks were low, systems from about 24 scanning lines to 60 lines were in use in the 1920. Baird’s system employed 30 image lines. Below you can see an actual photograph of such a Baird television image.
In spite of the low resolution, these first television images were astonishingly good in transmitting faces of persons and other close ups. Also, writings and drawings that were large enough could be transmitted well.
The screens displaying the early television images were only an inch or so wide and had to be viewed using a magnifying lens. Most of the early mechanical TV sets used a motor to rotate a metal disk with scanning holes to produce the picture, with a red or orange neon tube behind the disk to provide the light to build the image. Later mechanical systems also used lens disks, mirror drums and mirror screws, improving image brightness and size.
Radio Broadcasting began in the United States around 1920 on the medium wave band (also called AM radio band, 550-1500 kHz), and soon afterwards in Europe, in the same frequency band.
Early television signals had the distinct advantage that their image frequencies were located in the audio spectrum, that means, they could be heard as distinct chirping sounds. Such sounds could be transmitted on the radio, therefore, early television could also be transmitted over the regular radio transmitters already in existence.
The fascinating aspect of early television was that skilled radio amateurs could build themselves a mechanical television receiver and participate in the thrill of receiving images over the air! Many television kits were available at that time, all the amateur had to do was assemble it, connect it to a radio receiver, and watch television.
In England, regularly scheduled 30 line television programming were first broadcast by the BBC in September of 1929 using equipment supplied by John Logie Baird. At first, only the picture was transmitted for a few hours a week, after regular radio broadcasting was completed for the day. By March of 1930, sound and pictures were transmitted on two different radio frequencies. One therefore needed two radio receivers, one for the image, and the other one for the sound. The television broadcasts were all live broadcasts, television signal recording had not been achieved successfully just yet, and the Baird – BBC broadcasts came from a room in the basement of the BBC broadcast house. In 1933 Baird built a studio at Crystal Palace in London. These regular 30 line broadcasts in the Baird system continued until 1935 when they were shut down since the BBC announced that an all-electronic, high definition television system would replace the 30 line broadcasts.
In the United States all early television broadcasts were considered experimental, but in spite of this label, increasing numbers of television stations began television broadcasts, all over the country.
In1930, the US Federal Radio Commission allocated frequencies in the 2 mega cycle (2 MHz) band to experimental television, so higher image resolutions (48 and 60 line pictures) requiring a wider frequency band, stretching outside the spectrum needed for audio transmissions, could be attained.
By 1931, television was broadcast from about 25 stations in the US. These stations were not only broadcasting from major metropolitan areas in the East such as New York City, but they were also located in Iowa and Kansas. Several well respected manufacturers were selling fully assembled television sets and also kits.
TV broadcasts in the 2 MHz band could travel long distances, so reception was often possible hundreds of miles from the transmitting station. However, with long distance reception, the picture suffered from not only poor resolution, but also fading and ghosting.
In Europe, most countries had at least one mechanical television station, employing the 30 line standard, or other standards, up to 60 and even more lines.
Early television was not a major success, although it was quite a curiosity, and if received and displayed appropriately, very watchable. Except for some rare experimental disk recordings by John Logie Baird, no recordings of early mechanical television exist. It was said that due to the small image and low resolution, mechanical television had no entertainment value; this I would like to dispute. From eye witnesses and written reports it rather seems that early television programs were well written and staged; television plays of high quality were produced, and musical entertainment with well recognized artists of the time were presented. There is no dispute over the fact that the early television images flickered, and also suffered from image synchronization problems. However, faces could be well recognized, and movement in the image that cannot be reproduced in surviving still photographs, made the images much easier to watch. I also believe that not enough viewers at that time were able to enjoy this new form of entertainment, and therefore, not enough credit was given to the pioneers of early television.
By 1933 almost all experimental television stations stopped broadcasting in the US, and in 1936 the 2 MHz television band was re-assigned to police transmissions. The Baird 30 line TV programs stayed on the air in the UK until 1935, and the Soviet Union transmitted mechanical television until 1937.