Radio transmission of narrow-band mobile radio systems at 40 megacycles

MOBILE radio equipment manufactured in the period from 1946 to 1950 was designed for a 120-kc channel allocation in the 40-megacycle (mc) band. The receivers used with these systems had poor selectivity characteristics by today´s standards and are now referred to as ¿extra-wide-band¿ receivers. As mobile radio service expanded and the demand for frequency allocations increased, the inefficiency of this bandwidth assignment became evident. Accordingly the channel allocation was reduced to 40 kc, thus tripling the available number of frequency assignments. Initially, the Federal Communications Commission made assignments on an alternate-channel basis so as to allow 80-kc frequency spread between stations in the same geographical area. However, by 1951 most manufacturers were supplying equipment capable of working in a 40-kc channel assignment without being affected by systems on adjacent channels. Currently, receiver design has progressed to the point where 20-kc channel allocations, split-channel operation, appear to be feasible, and units of this type have been manufactured and placed in service.