Part 1 of this article provided context for the critical role of David Sarnoff, development of color TV, and RCA’s place in modern electronics; this part looks at the solution to the compatible color-TV challenge and the eventual corporate decline.

Problems met and solved

The first apparently intractable issue RCA had to solve was what we know as “encoding.” The monochrome TV signal was already defined within a 6-MHz bandwidth, with a complex analog shape that both carried the video information and also provided the horizontal and vertical synchronization signals. The TV receiver stripped these synch signals out via a clever scheme and used them to keep the displayed image lines and frame aligned with the TV camera’s scanning of the image.

How do you add complex color information within this fixed bandwidth, while not distorting or ruining the existing encoding? How do you do so in a way that is both backward and forward compatible, so that monochrome TV sets will render a color-encoded signal in proper grey-scale equivalent, while color receivers will display the conventional monochrome signal also with correct greyscale? That way, everyone would be happy, regardless of the TV they had or the signal being broadcast (today’s software developers could learn compatibility and upgrade lessons here!).

RCA scientists and engineers solved this problem with some extremely clever interleaving of signals within the bandwidth. They made extensive use of understanding how the eye and brain perceive color, detail, and motion (including the 1931 CIE chromaticity diagram) (Figure 1).

The circuitry to implement this at the transmitter and receiver was complicated, tube-based, and often frustrating (this was long before software, microcontrollers, or even basic digital circuits) but improved with time and experience (Figure 2). Key to piggyback/interleaving of the color-information signal was the use of a very accurate and stable, crystal-based color subcarrier at 315/88 MHz (usually described as 3.579545 MHz±10 Hz or about 3.58 MHz) – and a technique to continuously phase-synchronize it with the same signal when it was extracted from the received waveform.

That was only one step, but a big one. The next challenge was to actually conceive, design, build, and test the components which made the concept into reality. Here, they faced the dilemma of all communications systems: the components, topology, and circuitry of the transmitter side are very different than those of the receiver side, yet you can’t test one without the other. You have to have both ends working to verify that either one is working, so figuring out what’s working on a radically new system design is very difficult. Some of the many developments are called out in the Sidebar at the end, “Color TV required radical re-thinking, innovative design, and advanced manufacturing.”

There were also chemistry and production innovations. For example, electron-excited red, green, and blue color phosphors had to be developed, and a precise “shadow mask” with thousands of pinholes had to be chemically etched, placed, and perfectly aligned behind the CRT’s faceplate to create the image’s visible colors. Of course, low-cost high-voltage power supplies, such as 20 kV for the CRT and various high voltages for the other vacuum tubes (~50-100 V DC), were also needed. The basic color TV had about 100 tubes; the number was soon reduced by using so-called “dual tubes,” analogous to dual op amps.

The battle concludes

In 1953, both RCA and CBS presented their color-TV approaches to the FCC for approval. One presumed virtue of the spinning color-wheel approach that CBS demonstrated was that it was far less costly to build since it had far fewer components. It appeared at first glance to be more reliable and easier to repair. The RCA unit had over 100 vacuum tubes. It dissipated several hundred watts, while the CBS unit was a modified B&W TV with an added wheel, small motor, and some synchronization circuitry, and could, in theory, be retrofitted to existing sets. There were valid arguments for both approaches, and both RCA/NBC and CBS were also well-connected politically.

The final FCC decision was in favor of RCA’s all-electronic approach, since it offered a long-term roadmap, among other reasons, vindicating Sarnoff’s vision and RCA’s huge investment. The inherent, transparent backward/forward compatibility of the RCA approach with the 53 million monochrome sets already in homes was a huge advantage. With the decision, the NTSC (National Television System Committee) standard was set as the definition of color TV in the US (and soon Canada and Mexico). Europe followed a few years later with their own color systems, called PAL and SECAM, which were incompatible with the US standard.

The first color TVs went on sale in 1955 at $700 — a month’s salary for an average worker (Figure 3). They didn’t sell well, due to the cost and novelty, and they had performance and reliability issues. RCA cut the price to $500, boosted marketing, and did not flinch. Within a few years, the TV sets and sales improved, and having a color TV at home became the mark of “you’ve made it” or an indicator that your hotel was a “better” one (hotel ads and signs boasted of a “color TV in each room”).

Decline and disappearance

The conclusion to the story of color TV and the RCA/CBS battle is another complicated affair. Driven by the dream (hope? myth?) that some form of 1 + 1 = 3 synergy would occur when delivering products and services to the consumer, RCA was swept up in the conglomerate mania of the 1960s. They got involved with selling carpets, car rentals (they bought Hertz car rental in 1967), and many other businesses with little or no electronics connection. Within a few years, they were consumed with managing these disparate businesses and cut back on their technology investment and exposure. General Electric bought RCA in 1986 but soon sold it off in pieces.

Of course, it was not just misstepping that accounted for RCA’s misfortune. The development of the semiconductors, both transistors and ICs, and globalization changed the entire nature of the design and manufacturing of electronic products and their constituent components. RCA made several attempts to become a semiconductor supplier beginning in 1950. (Note that RCA was not the only failure in this respect, as none of the leading vacuum-tube vendors of the 1950s made a successful transition to being a major semiconductor vendor).

Today, we have the legacy of analog color TV, which still permeates many aspects of digital imaging. RCA itself is now just a trademark is owned by Technicolor (known as Thomson SA until January 2010), (Figure 4). They have gone from a worldwide name recognition that was probably as close to universal as a company can be to a “huh, who were they?” position — a humbling lesson for every market leader. So can you say what the position of Facebook and its cohorts will be in ten or twenty years? Sarnoff genuinely expected that color TV would bring art and culture to the masses who could not see them otherwise — so how has that prediction turned out?

 

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Sidebar: Color TV required radical re-thinking, innovative design, and advanced manufacturing

Among the color-TV transmitter-side innovations RCA pioneered were:

• the image orthicon, an RGB scanning camera;
• electronic filters which carefully shaped, passed, or attenuated signals so only desired parts of the spectrum, with the desired bandwidth and envelope, would be passed to the transmitter;
• new techniques for modulating the image information onto the carrier signal by combining AM, FM, and PM, using insightful understanding of why and where each modulation type was to be used (related to both electronic considerations as well as eye and ear tolerance for visual, color, and audio distortion);
• a technique to interlace the color information in alternate images frames, to reduce the bandwidth needed; again, knowledge of how color and detail are perceived was critical here;
• new broadcast-studio equipment, control panels, and complete cameras, each weighing several hundred pounds and mounted on special dollies, along with techniques for powering these kW-class units, and then keeping them cool (and adding more studio air conditioning, as well);
• new techniques for studio lighting and cast makeup, to better mesh with the subtleties of color-camera sensitivities and characteristics.

For the color-TV receiver, they developed:

• a radically new CRT, which used the B&W design as a starting point, but added:
• high-efficiency rare-earth color phosphors for each primary color (RGB), which glow when struck by electrons emitted by the CRT filament which were steered by its deflection coils;
• a way to precisely place thousands of triads of these RGB phosphors inside the CRT faceplate; each would be a picture element, or pixel;
• a thin, metal shadow mask with thousands of tiny etched holes to align with the phosphor-triad placement, and placed precisely about ¼ inch behind the inside of the CRT face; this acted as a mechanical screen to only allow the desired electron beam (RGB) to reach the intended phosphor in the triad;
• circuitry to demodulate the complex received AM/FM/PM signal, including stripping away the sync-signal portions
• extra circuitry which ensures backward compatibility, so a color TV receiving a monochrome-encoded signal would present a clean grey-scale image without an inadvertent color tint.
• a greatly improved channel-tuner design, which had to have more consistent frequency/phase performance and stability over time and temperature (this was an electromechanical device with dozens of inductors and capacitors; you had to get up and turn the knob to change channels).

 

EE World References

Teardown: Retro Portable CRT TV

Flyback power converters, Part 1: Basic principles

Flyback power converters, Part 2: Enhancements and ICs

Working with higher voltages, Part 1: Voltage boosters

Working with higher voltages, Part 2: Voltage multipliers

Cathode ray tube vs. flat screen displays in oscilloscopes

External References (and there are many, many more covering the business aspects, color TV development,  RCA history, timelines. technology, circuits, components, and consumer TV receivers)

1. David E. Fisher and Marshall Jon Fisher, “Tube: The Invention of Television” (excellent overview book)
2. Eugene Lyons, “David Sarnoff, a Biography”
3. The David Sarnoff Library
4. Ken Burns, “Empire of the Air: The Men Who Made Radio,” (PBS Video)
5. Tom Lewis, Empire of the Air: The Men Who Made Radio,” (companion to PBS video)
6. Kenneth W. Bilby, “The General: David Sarnoff and the rise of the communications industry”
7. com, “Color Television Receiver Block Diagram”
8. Vocal Technologies, “Analog TV Standards”
9. Wikipedia, “Color TV”
10. Wikipedia, “NTSC”
11. Science Direct, “Chrominance”
12. 1000Logos, “RCA”