You think you’ve got it tough?
By Bill Schweber, Technical Editor -- EDN, January 7, 1999
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 Recently, I read an excellent book on the invention of TV (Reference 1), which looks at the individuals, failures, advances, frustrations, companies, and rivalries that, incredibly, spawned today’s ubiquitous video system. Unlike the many books that gloss over technical issues, this book looks in adequate technical depth at key developments, such as photosensitive sensors, the scanning wheel, the CRT, the vidicon, and others.
Television’s early days particularly interests me, when the principles of TV as we know it were yet unknown to its inventors. After all, these inventors were not linearly refining some existing ideas; they were entering truly uncharted territory. How do you proceed when no one knows what the final answer looks like and when you can’t have a working prototype until you develop so many other pieces? It’s frustrating; a receiver is no good without its transmitter, yet they are quite different systems. Do you make progress by small steps or by large leaps of faith? Do you achieve success by modifying some rough ideas or by tossing out old ideas and starting over? The answer is all of the above, and more. The book occasionally discusses how TV inventors understood and measured what they had. One problem stands out to me. Key contributor Philo Farnsworth was puzzled that the crude image on his screen was always brighter in the middle than at either end of the scan line. (Incidentally, it was Farnsworth who had the "obvious" idea of using a line-by-line raster scan to convert a 2-D image into a single, time-varying signal.) Eventually, he realized that this situation existed because the sine wave controlled his line scan. The raster slewed faster at each end of the line, giving the electron beam less time to paint the CRT; it slewed slower, and thus lingered, at the middle. Farnsworth modified the sine-wave oscillator to a triangle-waveform source, and the problem went away. But the impressive thing is that Farnsworth figured out this solution by giving the problem a lot of thought. The oscilloscope—the tool you and I would reach for—was too crude to indicate the waveform’s raster shape and correlate it with the display image. That scope also had the sine-wave scan instead of the near-perfect linear ramp we have today. (The oscilloscope we automatically reach for didn’t even exist for much of TV’s early period!) So how did TV’s inventors know what signals were going in and coming out of any stage? The short answer is that inventing television wasn’t easy, but the designers didn’t know what they were lacking. We are so used to attaching fairly sophisticated test equipment to the designs we develop that we sometimes are spoiled. Most of today’s designers are refining designs or advancing on a linear, defined path. We insist that we need more and better tools to succeed on our journey. So, what happens when you take the road less traveled or the road not traveled at all? Read about how the electronics pioneers did it, and you’ll gain both an appreciation of their efforts and some new insights and approaches to dealing with your problems. Reference
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 Bill Schweber, Technical EditorYou can reach Technical Editor Bill Schweber at 1-617-558-4484, fax 1-617-558-4470, or bill.schweber@cahners.com. |
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