The first commercially operated mobile telephone network for private subscribers was opened by AT&T (American Telephone & Telegraph Corporation) and its associate company Southwestern Bell in St. Louis, Missouri, US, on June 17, 1946.

The network was initially based on six channels in the 150 MHz band but interference between them meant this eventually had to be reduced to three. Calls were switched manually, but the concept quickly spread, and by the end of the year AT&T had launched corresponding networks in 25 American cities. Six channels allowed a maximum of 250 subscribers. AT&T called this system MTS (Mobile Telephone Service); the phones were made by Motorola and were installed by Bell.

The first automatic mobile telephone system came into operation on March 1, 1948, in Richmond, Indiana. This system, known as Dial Direct, had been developed by Ramsey McDonald and worked without any manual intervention as long as calls were made between subscribers to the mobile system or stayed within the fixed local network to which the mobile system was connected.

Ramsey McDonald, formerly a senior engineer at the Police Radio Station in Richmond, had been urged by the local telephone company to develop the system. McDonald’s greatest problem seems to have been his relationship with the FCC, which had first given him permission to use the 152–162 MHz band for his experiments but then tried to impose such stringent requirements that his license would have been revoked.

The system was finally accepted on the condition that the central exchange was operated by an operator with a license for fixed telephony. McDonald’s example was followed several small companies, mainly trucking companies, around the US. In the 1950s, McDonald also installed his mobile system on a small scale in countries including Venezuela and Colombia. In 1964 the Bell companies introduced an upgrade MTS to IMTS (Improved Mobile Telephone Service), beginning in Harrisburg, Pennsylvania. IMTS enabled direct phoning and automatic channel switching, although with such a limited number of channels this restricted the system, by necessity, to only a very few users.

Author: Svenolof Karlsson & Anders Lugn

DESCRIPTION OF THE AMERICAN MOBILE SYSTEMS INTRODUCED IN THE 1960S

DESCRIPTION OF THE AMERICAN MOBILE SYSTEMS INTRODUCED IN THE 1960S

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