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The First Telephone Call Transmitted by Microwave (August 17, 1951)

On August 17, 1951 the first telephone call was placed on AT&T's microwave radio-relay skyway, the first facilities to transmit telephone conversations across the United States by radio rather than wire or cable. The new backbone telephone route, at the time the longest microwave system in the world, relayed calls along a chain of 107 microwave towers, spaced about 30 miles apart. AT&T spent about three years building it at a cost of $40 million.

The system was designed to carry television signals as well as telephone messages, and less than three weeks after the first phone call, on Sept. 4, 1951 more than 30 million people watched President Harry S. Truman deliver the opening speech at Japanese Peace Treaty conference held in San Francisco— the first transcontinental television broadcast.