Mobile Radio communication

The first experiments in radio communication with automobiles appear to have been made in 1921 by the Detroit police department. In 1927 the experiments were renewed and by April of 1928 the Detroit police had a system in successful operation. Experiments having proved the utility of the 30–40-megacycle band for car-to-land transmission; power utilities, traction companies, and others having use for emergency communication began making radiotelephone installations. An emergency radiotelephone service which for the first time provided connections to any telephone began operation in New York, N. Y., on December 5, 1940. In 1939, experiments indicated that frequency modulation held much promise and appeared to be superior to the conventional amplitude modulation employed up to that time for radiotelephone service from vehicles. Advanced techniques, overcrowding in the 30–40-megacycle band, and opening of the 152–162-megacycle band stimulated expansion.