Tuesday, May 31, 2011

More Telephone History (1878-1918)

A couple of weeks ago I pulled a piece out of a book I wrote about ten years ago titled Introduction to Telecommunications Networks. In that post I described the first year in the development of telephone technology. As a follow-up to that post, here's some of the major technical breakthroughs that happened between 1878 and 1918.

Bell sets up the first operator switching exchange and at the same time, Western Union Telegraph Company (http://www.westernunion.com) decided to use its existing national telegraph wire network to set up its own telephone company. Bell quickly sued Western Union and Western Union settled out of court, selling its network to Bell.

Henry Hummings in England gets a British patent for a variable resistance telephone transmitter that used finely ground carbon. The carbon transmitter solved many of the early problems Bell had trying to use liquid and electromagnetic transmitters. The carbon transmitter also used a voice cone attached to a diaphragm.

The diaphragm, which was attached to a conductor, vibrated with sound waves and caused the closed container of ground carbon to compress and uncompress changing resistance in the same way the liquid transmitters did.

American Telephone and Telegraph Company (http://www.att.com) was formed to provide long distance telephone service, connecting small Bell regional telephone franchises.

AT&T buys Henry Hummings’ ground carbon variable resistance telephone transmitter patent rights.

Thomas Edison modified Henry Hummings’ finely ground carbon transmitter by using larger carbon granules. The larger granules created more current paths with sound wave compression and therefore allowed more current to flow in conjunction with the compression. The larger granules also did not pack as tightly over time like the finely ground carbon in Hummings’ transmitter. When they did pack, usually lightly hitting the transmitter on a hard surface would loosen them up.

AT&T reorganizes, assuming the business and property of American Bell and becomes the parent company of the Bell System.

Siemens (http://www.siemens.com) first tests dialtone on the public switched telephone network in a German city.

AT&T patents an anti-sidetone solution for telephone receiver and transmitters. This technology allowed talkers to more easily adjust their voice volume when speaking into the telephone transmitter.

I'll continue with more history in a later post.

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