GOODALL, W. M.

Telephone by Pulse Code Modulation.

New York, American Telephone and Telegraph Company, 1947. 8vo. In the original printed blue wrappers. In "The Bell System Technical Journal", Volume XXVI, Number 3, October, 1947. Entire issue offered. Light miscolouring to spine and very light wear to extremities. A fine fine and clean copy. Pp. 395-409. [Entire issue: Pp. 395-691.].

First appearance of Goodall's early paper on the on telephones working by pulse code modulation (PCM).

PCM in the late 1940s and early 1950s used a cathode-ray coding tube with a plate electrode having encoding perforations.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.

Order-nr.: 50427