Quite a while back, I wrote Making Pictures Fly Through the Air, Part 1, which dealt with the development of a mechanical form of television. Starting with a concept designed by German engineering student Paul Nipkow long before radio itself, and later adapted for the airwaves by John Logie Baird and others. If you missed it, you might want to go back and read it first as it gives an understanding of how mechanical television would lead to the development of electronic television.
Mechanical television used a spinning wheel with a spiral pattern of holes drilled in it to scan an image one line at a time, and a similar device with a lamp behind it to reproduce that image. This system has several drawbacks. It was difficult given the technology of the day to keep the spinning wheels of the camera device and the reproducer device synchronized. The number of scan lines was limited to under 100, which compared to electronic TV's 525 lines, resulted in a very small, low resolution picture. Mechanical TVs were somewhat bulky and difficult to maintain. They were commercially produced in limited quantity and never really caught on with the general public.
Electronic television, that which requires no moving parts, would require the development of both a camera and an image-reproducing device. Electronic TV retained the concept of breaking down an image into a series of scanned lines, each transmitted sequentially, but done so fast as to appear to the eye as a solid image.
Electronic television was not the invention of any one individual, but rather the work of many, some in collaboration, but most working independently. In this article, I'll try to give an overview of the major players and what they contributed to the art. It would be outside the scope and available space of this article to try and cover everyone who contributed.
It was already known that when electrons strike certain phosphors, they cause them to glow, an effect that we take for granted every time we turn on a fluorescent lamp. In 1897, German scientist Karl Ferdinand Braun developed the cathode ray tube (CRT). This device is a vacuum tube that uses electrons emitted by an element called a cathode, to be formed into a beam and finely focused on a target surface coated with a phosphor.
In the earliest cathode ray tubes, the electron beam passed between four plates which when electrically charged, could be used to be used to bend, or steer the beam. Using this method, known as electrostatic deflection, the beam could be swept across the phosphor screen to form lines.
The first use for the CRT was not for displaying pictures, but rather for displaying the wave shapes of electrical signals on an instrument known as an oscilloscope. The first CRTs used a green-colored phosphor that was highly efficient and did not require a powerful beam to make it glow brightly.
Green pictures, however, would not be very appealing to the general public. What would be needed was a bright, white, glowing phosphor that would be dark in color when not illuminated.
In 1907, in what is believed to be the first electronic reproduction of an image on a CRT, Russian scientist Boris Rosing used the CRT combined with a Nipkow wheel mechanical television camera, to reproduce some crude pictures of geometric shapes.
In 1929 another Russian scientist, Vladimir Kosma Zworykin, who had fled Russia during the Revolution, was now working for George Westinghouse. Inspired by Rosing's work, Zworykin developed what he named the "kinescope," one of the first functional white phosphor cathode ray tubes for television work. He also began work on a matching camera tube bearing the same name.
Four years later, Allen B. DuMont, an oscilloscope and test-instrument maker, would refine Zworykin’s cathode ray tube into the first practical and reproducible picture tube. It used a phosphor that was dark green in appearance when not illuminated, and produced a bright, white light when struck by electrons. It would become known as type "P4" by the electronics industry. Such a phosphor would result in a black and white picture with good contrast.
The last major improvement to the black and white picture tube, prior to the development of a working TV system, was made by William Coolidge. He was already successful in the development of tungsten filaments for light bulbs, which he had patented in 1903, greatly improving the performance of Edison's carbon filament bulb. In 1935, he obtained a patent for incorporating this filament technology into cathode ray tubes.
As if the fact that mechanical TV was invented by a college student in 1884, predating radio itself, isn't amazing enough, the invention of the system for transmitting analog electronic TV in the United States would be the work of an American high school student in 1923. Keep in mind that broadcast radio itself, was only three-years-old at that time.
Philo T. Farnsworth was born on August 19, 1906, to Mormon farmers, Lewis and Serena Bastian Farnsworth, in a small community near Beaver, Utah. In 1918, the family moved to a relative's 250-acre ranch in Rigby, Idaho. The 12-year-old Philo was delighted to find his new home electrified with its own but somewhat troublesome generator. He quickly taught himself how to repair and maintain the device. Fascinated by this new technology called radio, he read every technology magazine and book that he could get a hold of. By the time he entered Rigby High School, he had become interested in mechanical television. Even at this age though, he recognized the limitations of the system and the need for an all electronic system with no moving parts.
While in high school, Farnsworth excelled at physics and chemistry. The school did not have an electronics instructor, so at one point Philo presented his detailed drawings of his concept for electronic TV to his chemistry teacher. The drawings were said to have occupied several full-size blackboards and included the entire system, camera to receiver. The impressed, if not overwhelmed, teacher encouraged Philo to pursue his idea and apply for a patent. The teacher also kept sketches of the drawings, which later would come in handy when corporate giant RCA would challenge Farnsworth's patent.
After high school, Farnsworth attended Brigham Young University, and during his first year also completed a correspondence course with The National Radio Institute to become a certified radio repair technician. Farnsworth began to put great effort into developing a practical electronic television camera. Having excelled at chemistry in both high school and college, it gave him an advantage over other inventors in his understanding of how certain chemicals reacted to light. With $6,000 from investors, Mr. Farnsworth set up a lab in 1927 to develop his camera tube, which he named the" image dissector."
By 1929, he was able to display some images from the device. Since investors were pressuring him as to when they would see a return on their investment, his first transmission was that of a still image of a dollar sign. He also demonstrated a moving image of his wife, Elma. His camera produced satisfactory images, but had one disadvantage: it lacked sensitivity and required extremely bright lights to make it work. Lights so bright, that they were uncomfortable for actors to work in front of.
During this same time period, Vladimir Zworykin was also busy at work. When he had fled Russia, he took his kinescope camera with him. Zworykin had visited Farnsworth's lab and was impressed by the image dissector. In a deal between RCA and Westinghouse, Mr. Zworykin went to work developing a camera tube for RCA. If you have read a few of my other articles, you can probably already smell the patent litigation coming.
Combining the best features of the image dissector and the kinescope cameras, Zworykin developed the "iconoscope" camera, which worked with reasonable, or perhaps better to say tolerable, levels of light. The lawsuits began nearly 10 years before TV would be demonstrated to the general public. In the end, courts ruled in Mr. Farnsworth's favor, and RCA would have to pay him royalties.
This would be as far as camera technology would go prior to World War II.
Between 1923 and 1927, several inventors, both foreign and domestic, demonstrated hybrid systems using Nipkow wheel cameras and CRT displays, but due to the limitations of the Nipkow system, were limited in resolution. In 1931, four years after Mr. Farnsworth demonstrated his all-electronic system to peers and investors, German inventor Manfred Von Ardenne is credited with the first demonstration of a similar system to the general public at the Berlin Radio Show. He is credited by some as having broadcast parts of the 1936 Berlin Olympics to several viewing rooms using his system; however. sources confirming this are somewhat vague, and most say that the quality was poor. Philo Farnsworth demonstrated his system during a 10-day long exhibit at the Franklin Institute of Philadelphia in August of 1934.
In 1939, RCA announced the beginning of experimental broadcasts in New York City, using Philo Farnsworth's system. There was still some debate over the number of scan lines that would be used to make up a TV picture. The Radio Manufacturers Association organized a committee to develop a standard in 1936. Four years later, it became known as the National Television Standards Committee (NTSC), which adopted 525 scan lines as the standard for U.S. television in 1941.
Despite the efforts of RCA to develop cameras and transmission systems, it was smaller manufacturers who introduced receivers to the American public. Radio manufacturer Frank Angelo D. Andrea, whose company was well-known for its line of popular consumer table radios bearing his initials, FADA, introduced a TV with a three-inch screen at the 1939 New York World’s Fair.
As pictured above, it sold for $189, but was available in kit form as Model KT-E5 with a wooden face and open chassis for $79, tubes not included. Hallicrafters, a company that made radio receivers that were favorites with short wave listeners and amateur operators, introduced their own three-inch screen TV shortly after. Others joined in, and over the next two years, screen sizes grew to six inches.
Picture tubes contain a very high vacuum, so the surrounding atmosphere exerts tremendous pressure on them. The Corning glass company developed a high-strength glass, similar to Pyrex, to make manufacturing possible. Later on, larger tubes would use thick, high-strength glass, similar to that used in car windows.
Then came World War II, which put a halt to all further TV production and development. The technological development as a result of the war effort though, set the stage for the TV boom that would follow.
These contributions included bigger picture tubes – developed for war time radar screens – highly sophisticated tubes that were small and durable, and the miniaturization of many other components to make post-war TV sets practical and affordable.
The big manufacturers, fat with profits from military contracts, would hit the ground running. Zenith, RCA, war-time tube maker Sylvania, GE, and Philco would quickly outpace smaller companies in TV production. Picture tube size would increase at about two to four inches per year until maxing out around 27 inches. By 1949, electromagnetic coils mounted on the outside of the picture tube were replacing the internal electrostatic plates as a method of steering the electron beam. They could bend the beam more effectively and would allow for the manufacture of much larger picture tubes. Electromagnetic deflection was also a carryover from WWII radar development.
Philo Farnsworth was by this time considered to be “father of American television.” He passed away in 1971, having been granted nearly 100 TV-related patents.
Here is a bit of TV trivia: Why do TV channels start with channel 2? Originally they started with channel 1, which was centered at 25 MHz. Both the Andrea and Hallicrafter sets mentioned above came with channel 1. There were two primary reasons that channel 1 was dropped.
First, 25 MHz behaves more like a short wave frequency and can travel great distances under the right conditions, allowing distant stations to interfere with one another. Secondly, other uses, ones more suitable for the frequency, were developed during the war and would continue afterwards. Post-war, the FCC assigned channel 2, at 54 MHz to be the first TV channel. Since so few pre-war sets were made, it puzzles me as to why manufacturers simply did not renumber the channels. Finding a TV with channel 1 is a positive way to identify that you have a rare prewar set.