This paper extends a simple mathematical treatment of the problem of cochannel interference in land mobile radio presented earlier, in which the interdependence between frequency reuse distance and required protection ratio was developed. By considering realistic patterns of frequency assignment, it is demonstrated that, for a given grade of service, spectrum economy is a discontinuous function of protection ratio, thus the precise value of protection ratio may not be as important as it first appears. Properties of different modulation systems are compared from this standpoint and the superiority of s.s.b. over f.m. tentatively indicated in the earlier communication, is confirmed.