Pulse-code modulation: Difference between revisions

Revision as of 01:19, 17 March 2025

Revision as of 14:29, 12 April 2025

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The first transmission of [[speech]] by digital techniques, the [[SIGSALY]] encryption equipment, conveyed high-level [[Allies of World War II|Allied communications]] during [[World War II]]. In 1943 the [[Bell Labs]] researchers who designed the SIGSALY system became aware of the use of PCM binary coding as already proposed by Reeves. In 1949, for the Canadian Navy's [[DATAR]] system, [[Ferranti Canada]] built a working PCM radio system that was able to transmit digitized radar data over long distances.<ref>{{cite book |author=Porter, Arthur |title=So Many Hills to Climb |date=2004 |publisher=Beckham Publications Group |isbn=9780931761188}}{{page needed|date=September 2017}}</ref>

PCM in the late 1940s and early 1950s used a [[Cathode ray tube|cathode-ray]] [[:File:US02632058 Gray.png|coding tube]] with a [[plate electrode]] having encoding perforations.<ref>{{cite book journal|url=https://archive.org/details/bstj27-1-44 |author=Sears, R. W. |workjournal=Bell Systems Technical Journal |volume=27 |title=Electron Beam Deflection Tube for Pulse Code Modulation |pages=44–57 |publisher=[[Bell Labs]] |date=January 1948 |access-date=14 May 2017}}</ref> As in an [[oscilloscope]], the beam was swept horizontally at the sample rate while the vertical deflection was controlled by the input analog signal, causing the beam to pass through higher or lower portions of the perforated plate. The plate collected or passed the beam, producing current variations in binary code, one bit at a time. Rather than natural binary, the grid of Goodall's later tube was perforated to produce a glitch-free [[Gray code]] and produced all bits simultaneously by using a fan beam instead of a scanning beam.<ref>{{cite bookjournal |url=https://archive.org/details/bstj30-1-33 |author=Goodall, W. M. |workjournal=Bell Systems Technical Journal |volume=30 |title=Television by Pulse Code Modulation |pages=33–49 |publisher=[[Bell Labs]] |date=January 1951 |access-date=14 May 2017}}</ref>

In the United States, the [[National Inventors Hall of Fame]] has honored [[Bernard M. Oliver]]<ref>