Electronics Guide

The Nipkow Disk

The conceptual foundation for mechanical television came from Paul Nipkow, a German engineering student who patented his "electric telescope" in 1884. Nipkow's system used a spinning disk with a spiral pattern of small holes. As the disk rotated, each hole swept across a different horizontal line of the image being scanned. Light passing through the holes struck a selenium cell, converting the light variations into electrical signals.

At the receiving end, a similar disk rotating in synchronization with the transmitter's disk would reconstruct the image. A light source behind the receiving disk varied in brightness according to the incoming electrical signal, and the spiral holes allowed the eye to perceive a complete image through the phenomenon of persistence of vision. While Nipkow himself never built a working system, his disk became the basis for virtually all mechanical television experiments that followed.

The simplicity of the Nipkow disk made it attractive to experimenters, but it also imposed severe limitations. The disk had to be large to achieve reasonable image size, yet it needed to rotate at high speed to provide adequate frame rates. The number of holes determined the number of scan lines, and adding more holes reduced the amount of light reaching the photocell, degrading signal quality. These fundamental constraints meant that mechanical television could never achieve the image quality that electronic systems would later provide.

Baird's Television System

The most prominent figure in mechanical television was John Logie Baird, a Scottish inventor whose determination and showmanship brought television to public attention in the 1920s. Working with limited resources in cramped quarters, Baird assembled his first experimental apparatus from salvaged materials including a tea chest, biscuit tin, darning needles, and cardboard disks held together with sealing wax.

In October 1925, Baird achieved the first true television image when he transmitted a recognizable picture of a ventriloquist's dummy he called "Stookie Bill." The following January, he demonstrated his system to members of the Royal Institution in London, the first public demonstration of a working television system. In 1928, Baird achieved the first transatlantic television transmission, sending an image from London to New York, and also demonstrated color television using a system with colored filters on the scanning disks.

Baird's mechanical system used a Nipkow disk with a modest number of holes, typically thirty, producing an image of thirty lines. While this resolution was barely adequate for recognizing faces, it was sufficient for Baird to generate enormous public interest in television. The British Broadcasting Corporation began experimental broadcasts using Baird's system in 1929, and regular service commenced in 1932.

Despite Baird's pioneering work and commercial success, his mechanical approach was fundamentally limited. The thirty-line images were dim, small, and of poor quality by any objective measure. Baird continued developing improved mechanical systems, including a mirror-drum scanner and a system using a film intermediate, but none could match the potential of electronic television. When the BBC evaluated both mechanical and electronic systems in 1936, the electronic approach proved decisively superior, and Baird's mechanical broadcasts ended in 1937.

Other Mechanical Television Pioneers

While Baird achieved the greatest public recognition, other inventors pursued similar approaches. Charles Francis Jenkins in the United States demonstrated mechanical television as early as 1923 and began experimental broadcasts in 1928. His company manufactured receivers and promoted television enthusiastically, though his systems suffered from the same limitations as Baird's.

In Germany, Denes von Mihaly developed mechanical television systems and demonstrated them at the Berlin Radio Exhibition in 1928. The German post office began experimental television broadcasts in 1929, using both Mihaly's equipment and systems developed by other inventors. The Soviet Union also pursued mechanical television, with broadcasts beginning in Moscow in 1931.

These various mechanical television systems shared common characteristics: low resolution, dim images, small picture size, and the mechanical complexity inherent in high-speed rotating components. While they proved that television was possible and generated public excitement about the technology, they were destined to be replaced by electronic systems that offered fundamentally superior performance.

Philo Farnsworth's Vision

Philo Taylor Farnsworth conceived the fundamental principle of electronic television at the remarkably young age of fourteen, while plowing a field on his family's Idaho farm in 1921. Looking at the parallel rows of the plowed field, he realized that an image could be captured and transmitted line by line, much as his plow turned the soil row by row. This insight led him to envision a system where an electron beam would scan an image in horizontal lines, converting the light values into electrical signals that could be transmitted and reassembled at a receiver.

Farnsworth lacked the resources to pursue his idea immediately, but he shared his concept with his high school chemistry teacher, Justin Tolman, who recognized the brilliance of the young inventor's thinking. After completing high school and studying at Brigham Young University, Farnsworth found financial backers who provided the resources to develop his ideas into working hardware.

On September 7, 1927, at his laboratory in San Francisco, Farnsworth achieved the first fully electronic television transmission when he successfully transmitted the image of a simple straight line. When one of his investors asked when they would see some return on their investment, Farnsworth reportedly pointed to the image and replied, "There you are, electronic television!" Further demonstrations followed, including the transmission of a dollar sign that delighted his backers.

Farnsworth's system used his invention of the image dissector, a camera tube that converted optical images into electrical signals through the photoelectric effect. While the image dissector had limitations, particularly its low sensitivity requiring very bright illumination, it worked entirely without any mechanical components and demonstrated the viability of all-electronic television.

Vladimir Zworykin's Contributions

Vladimir Kosma Zworykin brought both scientific training and corporate resources to the development of electronic television. Born in Russia and trained as an electrical engineer under Boris Rosing, who had experimented with cathode ray tube displays as early as 1907, Zworykin emigrated to the United States after the Russian Revolution and joined the Westinghouse Electric Corporation.

In 1923, Zworykin filed a patent application for an electronic television system, including a camera tube he called the iconoscope and a display tube he called the kinescope. However, the iconoscope described in this early patent did not work as specified, and considerable development would be required before Zworykin could demonstrate a practical system.

Zworykin moved to the Radio Corporation of America (RCA) in 1929, where he led a well-funded research team working on television development. When David Sarnoff, RCA's president, asked Zworykin how much it would cost to develop a practical television system, Zworykin estimated one hundred thousand dollars. The actual cost would exceed fifty million dollars before RCA's television system was ready for commercial deployment.

Despite his early patent filings, Zworykin's working iconoscope was not demonstrated until 1933, years after Farnsworth's successful demonstrations. The resulting patent dispute between Farnsworth and RCA continued for years, with RCA ultimately being forced to take a license from Farnsworth in 1939, a rare instance of RCA paying patent royalties to an independent inventor rather than the reverse.

Parallel Development

While Farnsworth and Zworykin were the most prominent figures in American electronic television development, important work occurred simultaneously in other countries. In Britain, EMI engineers Isaac Shoenberg and his team developed the Emitron camera tube, similar in principle to Zworykin's iconoscope but developed independently. The EMI system would become the basis for British electronic television broadcasting.

In Germany, Manfred von Ardenne demonstrated an all-electronic television system in 1931, and German engineers developed both camera tubes and display systems in parallel with American and British work. Japan also conducted television research during this period, with NHK broadcasting experimental transmissions beginning in 1939.

The Iconoscope

Zworykin's iconoscope used a mosaic of tiny photosensitive elements deposited on a mica sheet inside the tube. Each element accumulated electrical charge in proportion to the light falling upon it, storing the image until it could be read out by a scanning electron beam. When the beam struck each element in turn, it neutralized the stored charge, creating a signal current proportional to the brightness at that point in the image.

This charge-storage principle gave the iconoscope much higher sensitivity than Farnsworth's image dissector, which could only use the electrons generated at the instant the beam scanned each point. However, the iconoscope had its own problems, including spurious signals caused by secondary electrons and shading effects that made it difficult to achieve uniform illumination across the image.

The iconoscope required very bright lighting, typically several times the intensity of normal daylight, making it impractical for many subjects. Television studios of the era became notorious for their blazing lights and intense heat, challenging performers and limiting the types of productions that could be televised.

The Image Orthicon

The limitations of the iconoscope drove development of improved camera tubes. The image orthicon, developed at RCA by Albert Rose and his colleagues in the early 1940s, combined the charge-storage principle with electron multiplication to achieve sensitivity hundreds of times greater than the iconoscope. An image orthicon could produce acceptable pictures under normal room lighting conditions, revolutionizing television production.

The image orthicon worked by focusing an optical image onto a photocathode, which emitted electrons in proportion to the light intensity at each point. These electrons struck a target plate, creating a charge pattern that was then read by a low-velocity scanning beam. The return beam, modulated by the stored charge, passed through an electron multiplier that amplified the signal before it left the tube.

This tube dominated television broadcasting from its introduction after World War II until the development of solid-state imaging devices in the 1970s and 1980s. Its high sensitivity enabled television to move out of studios and cover news events, sports, and other programming that would have been impossible with earlier camera tubes.

Cathode Ray Tube Principles

A cathode ray tube generates a beam of electrons from a heated cathode and accelerates them toward a phosphor-coated screen. When electrons strike the phosphor, it emits light. The electron beam is deflected horizontally and vertically by magnetic or electrostatic fields, allowing it to scan across the screen in the same pattern used by the camera to capture the image.

The intensity of the electron beam is modulated by the incoming video signal, so that the phosphor glows brightly where the image should be bright and dimly where it should be dark. Persistence of vision combines the rapidly traced lines into the perception of a complete, continuous image.

Television Receiver Development

Early television receivers were expensive, complex, and temperamental. The cathode ray tube itself was costly to manufacture, requiring precise assembly of multiple components within a highly evacuated glass envelope. The tubes had to withstand the high voltages needed to accelerate electrons to sufficient energy to excite the phosphor brightly, typically ten thousand volts or more for a modest-sized tube.

Early television screens were small, often only seven or nine inches measured diagonally, and the images were typically green or orange depending on the phosphor used. Black-and-white displays with approximately correct gray scale required development of appropriate phosphor materials and careful control of the electron beam characteristics.

Receiver circuits were also complex, requiring multiple stages of radio frequency amplification, a local oscillator and mixer for superheterodyne reception, intermediate frequency amplification, video detection, video amplification, and synchronization separation. All of this had to be achieved with the vacuum tubes of the era, resulting in receivers containing twenty or more tubes that consumed substantial power and generated considerable heat.

Early Standards Confusion

Before standards were established, different developers used whatever parameters suited their equipment. Early mechanical systems typically used between thirty and sixty lines, while electronic systems could achieve much higher resolution. Frame rates varied from fifteen to thirty frames per second. This chaos made it impossible for receivers to work with more than one type of transmission.

The number of scan lines represented a fundamental trade-off. More lines meant higher resolution but required more bandwidth to transmit and more sophisticated equipment to generate and display. The frame rate had to be high enough to avoid visible flicker, but higher frame rates also required more bandwidth. Engineers sought the minimum parameters that would produce acceptable image quality.

American Standards

In the United States, the Radio Manufacturers Association formed a committee in 1936 to recommend television standards. After extensive study and debate, the committee initially recommended 441 lines at thirty frames per second. However, continuing technical advances led to revisions, and in 1941, the National Television System Committee (NTSC) established the standard of 525 lines at approximately thirty frames per second (actually 29.97 frames per second, related to the sixty-hertz power line frequency).

The American standard used interlaced scanning, in which each frame was transmitted as two interlaced fields of alternating lines. This doubled the apparent frame rate without increasing bandwidth, reducing flicker while maintaining image resolution. Interlaced scanning would remain the standard for analog television throughout its existence.

European Standards

European countries adopted different standards, typically with more scan lines but lower frame rates due to the fifty-hertz power line frequency common in Europe. Britain initially used 405 lines at twenty-five frames per second before later moving to 625 lines. France briefly used an 819-line system, the highest resolution analog television standard ever deployed, before eventually harmonizing with the rest of Europe on 625 lines.

These incompatible standards meant that television programming could not easily cross national boundaries and that equipment designed for one market would not work in another. This fragmentation persisted throughout the analog television era and created ongoing challenges for international broadcasting and equipment manufacturers.

British Broadcasting Corporation

The BBC conducted the world's first regular high-definition television service, beginning on November 2, 1936, from Alexandra Palace in London. Initially, the service alternated between Baird's mechanical system and EMI's electronic Marconi-EMI system on a weekly basis, allowing direct comparison. The electronic system quickly proved superior, and mechanical television was abandoned in February 1937.

The BBC's pre-war television service reached only a limited area around London and attracted only about twenty thousand viewers before broadcasting was suspended at the outbreak of World War II in September 1939. Nevertheless, it demonstrated that regular television broadcasting was practical and established operational procedures that would be refined after the war.

American Broadcasting

In the United States, NBC began experimental broadcasts from the Empire State Building in New York in 1936. The most notable pre-war broadcast was the opening of the 1939 New York World's Fair, where President Franklin D. Roosevelt became the first American president to appear on television. Regular NBC service began on April 30, 1939, though programming was limited and receivers were expensive.

CBS and other broadcasters also began television operations, though commercial broadcasting remained limited until after World War II. The Federal Communications Commission authorized commercial television in 1941, and stations began selling advertising time, but the war soon interrupted further development.

German Television

Germany developed television actively during the Nazi era, driven partly by the regime's recognition of the medium's propaganda potential. German television achieved notable technical accomplishments, including extensive coverage of the 1936 Berlin Olympics, which was shown in public viewing rooms throughout Berlin. However, German television never achieved widespread home reception before the war ended all broadcasting.

The 1936 Berlin Olympics

The 1936 Summer Olympics in Berlin represented the first major television outside broadcast. German engineers deployed cameras at various Olympic venues and transmitted coverage to public viewing rooms in Berlin and other German cities. While the image quality was limited by the technology of the time, the broadcasts demonstrated television's potential for bringing distant events to audiences who could not attend in person.

The technical challenges of broadcasting from multiple outdoor locations pushed the limits of existing camera technology and transmission equipment. The success of the Olympic broadcasts, despite these challenges, encouraged further investment in television development across Europe and America.

Mechanical Color Systems

The earliest color television experiments used mechanical approaches, typically involving rotating color filter wheels synchronized between camera and receiver. John Logie Baird demonstrated a mechanical color television system as early as 1928, using spiral filters on his scanning disks to capture and display sequential red, green, and blue images that the eye combined into color.

Peter Goldmark at CBS developed a more refined mechanical color system in the late 1940s, using a rotating color disk in front of both the camera and the receiver's cathode ray tube. This system produced excellent color quality for its time and was briefly approved as the American color television standard in 1950. However, its mechanical complexity and incompatibility with existing black-and-white receivers led to its eventual abandonment in favor of electronic color systems.

Electronic Color Approaches

Electronic color television required developing camera tubes that could separately capture red, green, and blue image components, and display tubes that could reproduce these colors. Various approaches were explored, including tubes with multiple electron guns aimed at interleaved color phosphor stripes, and projection systems that combined separate red, green, and blue images.

RCA developed the shadow mask color tube, which used a perforated metal mask to direct electrons from three separate guns to the appropriate red, green, or blue phosphor dots on the screen. This technology would eventually become the basis for color television receivers, but it was not ready for commercial deployment until the 1950s. The pre-war period saw only experimental demonstrations of electronic color television.

Mechanical versus Electronic

The first major standards conflict was between mechanical and electronic television. Proponents of mechanical systems, led by Baird in Britain and Jenkins in America, argued that their technology was proven and ready for deployment. Electronic television advocates, including RCA in America and EMI in Britain, contended that only electronic systems could achieve the image quality necessary for successful broadcasting.

The British solution was to test both systems in parallel, which quickly demonstrated electronic television's superiority. In America, the transition was less dramatic, as mechanical television never achieved the same level of commercial deployment. By 1937, the question was settled in favor of electronic television, though the investment made in mechanical systems by some broadcasters and manufacturers became worthless.

Resolution and Bandwidth Debates

Even after electronic television was established, debates continued over specific parameters. Higher resolution required more bandwidth, limiting the number of channels that could fit in the available radio spectrum. Broadcasters who had already invested in lower-resolution equipment resisted changes that would obsolete their systems, while manufacturers of more advanced equipment pushed for higher standards.

These debates were complicated by patent considerations, as different parameters might favor equipment covered by different patents. The eventual standards represented compromises among technical, commercial, and political considerations rather than purely optimal engineering solutions.

Receiver Costs and Availability

Early television receivers were expensive, typically costing the equivalent of several months' wages for an average worker. The sets were also complex, requiring regular adjustment and maintenance. The cathode ray tubes had limited lifespans and were expensive to replace. These factors limited television ownership to wealthy early adopters.

Manufacturers offered various receiver configurations to reach different price points. The smallest and cheapest sets had tiny screens, sometimes only three inches diagonal, and used magnifying lenses to enlarge the image. Larger sets with bigger tubes cost proportionately more. Some manufacturers offered kit versions for technically inclined hobbyists who could save money by assembling the receivers themselves.

Limited Programming

Early television stations broadcast only a few hours per day, and programming was often rudimentary. The production techniques later taken for granted had not yet been developed, and many broadcasts consisted of little more than someone talking directly to the camera. Live drama, musical performances, and news presentations gradually developed, but the art of television production was still in its infancy.

The high cost of program production and the small potential audience made television economically challenging. Broadcasters struggled to find sustainable business models, and advertising revenue was minimal given the limited number of viewers. Government support, as with the BBC in Britain, or cross-subsidy from radio operations, as with NBC in America, was necessary to sustain television broadcasting during this developmental period.

Geographic Limitations

Television signals, transmitted at very high frequencies, did not follow the curvature of the Earth and could not be reflected from the ionosphere like lower-frequency radio signals. This meant that television reception was essentially limited to line-of-sight from the transmitter, typically no more than fifty to one hundred miles depending on terrain and transmitter power.

Before the development of network interconnection, each station had to produce its own programming or rely on film recordings of programs produced elsewhere. The infrastructure for national television networks would not be built until after World War II, when coaxial cables and microwave relay systems could carry television signals across countries.

War Interruption

World War II brought civilian television development to an abrupt halt. In Britain, the BBC television service was shut down on September 1, 1939, famously cutting off mid-program when war was declared. In America, commercial television, which had just begun, was suspended as manufacturing capacity was redirected to military production.

However, the war also accelerated technology development in related areas. Radar systems, which used similar cathode ray tube displays, drove improvements in tube technology and manufacturing. Electronics production capacity expanded enormously to meet military needs. When the war ended, both the technology and the manufacturing infrastructure for television had advanced significantly, setting the stage for rapid postwar expansion.