Editing Fax (section)

=== Telephone transmission ===

{{External media|image1=[http://digitalprinting.blogs.xerox.com/wp-content/uploads/sites/3/2012/08/Xerox-LDX-Image.jpg LDX system, Scanner and Printer]|image2=[https://biztechmagazine.com/sites/default/files/Q0416-BT-TOT-Xerox-What.jpg Magnafax Telecopier by Xerox]}}
In 1964, Xerox Corporation introduced (and patented) what many consider to be the first commercialized version of the modern fax machine, under the name (LDX) or Long Distance Xerography.  This model was superseded two years later with a unit that would set the standard for fax machines for years to come.  Up until this point facsimile machines were very expensive and hard to operate. In 1966, Xerox released the Magnafax Telecopiers, a smaller, {{cvt|46|lb}} facsimile machine.  This unit was far easier to operate and could be connected to any standard telephone line.  This machine was capable of transmitting a letter-sized document in about six minutes. The first sub-minute, digital fax machine was developed by [[Dacom]], which built on digital data compression technology originally developed at [[Lockheed Corporation|Lockheed]] for satellite communication.<ref name="etd.ohiolink.edu">[https://etd.ohiolink.edu/rws_etd/document/get/ohiou1183661772/inline ''The implementation of a personal computer-based digital facsimile information distribution system''] {{Webarchive|url=https://web.archive.org/web/20160303231649/https://etd.ohiolink.edu/rws_etd/document/get/ohiou1183661772/inline |date=2016-03-03 }} – Edward C. Chung, [[Ohio University]], November 1991, page 2</ref><ref name="Fax 1971, Pages 112-114">''Fax: The Principles and Practice of Facsimile Communication'', Daniel M. Costigan, Chilton Book Company, 1971, pages 112–114, 213, 239</ref>

Analog facsimile machines worked by optical scanning of a document or drawing spinning on a drum. The reflected light, varying in intensity according to the light and dark areas of the document, was focused on a [[photocell]] so that the current in a circuit varied with the amount of light. This current was used to control a tone generator (a [[modulator]]), the current determining the frequency of the tone produced. This audio tone was then transmitted using an [[acoustic coupler]] (a speaker, in this case) attached to the microphone of a common [[Handset|telephone handset]]. At the receiving end, a handset's speaker was attached to an acoustic coupler (a microphone), and a [[fax demodulator|demodulator]] converted the varying tone into a variable current that controlled the mechanical movement of a pen or pencil to reproduce the image on a blank sheet of paper on an identical drum rotating at the same rate.