Wireless transmission

Wireless transmission
As a designer for the Radio Corporation of America (RCA), in 1924, Richard H. Ranger invented the wireless photoradiogram, or transoceanic radio facsimile , the forerunner of today’s "Fax" machines. A photograph of President Calvin Coolidge sent from New York to London on November 29, 1924 became the first photo picture reproduced by transoceanic radio facsimile. Commercial use of Ranger’s product began two years later. Radio fax is still in common use today for transmitting weather charts and information. Also in 1924, Herbert E. Ives of AT&T transmitted and reconstructed the first color facsimile, using color separations.
Prior to the introduction of the once-ubiquitous fax machine, one of the first being the Exxon Qwip in the mid-1970s, radio 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 would vary 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 telephone handset . At the receiving end, a handset’s speaker was attached to an acoustic coupler (a microphone), and a demodulator converted the varying tone into a variable current which 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. A pair of these expensive and bulky machines could only be afforded by companies with a serious need to communicate drawings, design sketches or signed documents between distant locations, such as an office and factory.