The History of Land-Mobile Radio Communications

This paper on land-mobile radio communications was prepared for the noncommunications and nonmobile radio specialist. The early pioneering work of the police is covered, and after a brief statement about the early use of mobile transmitters, the Connecticut State Police two-way FM system is described. From the introduction of FM into the Connecticut system to the present, engineering efforts have been directed toward the improvement of selectivity, the elimination of spurious responses and spurious radiation of the equipment, and in general, toward technical improvements which would make possible both an increase in spectrum utilization and an increase in channel loading. In the more recent embodiments of equipments, transistors have been used for the power supply, for audio amplifiers, and for complete receiver circuit design. While the use of single-sideband modulation and the general characteristics of random-access systems are under investigation, advantages have not been disclosed which would justify a switch from FM to some other modulation system. The efficiency of frequency utilization must be increased, and any system which offers a substantial improvement over FM will be given careful attention.