jamming techniques. As we mentioned ear- lier, many historians believe that FM radio was crucially important to the Allies' success in World War II. Radio's Evolution Radio is often viewed as having evolved in two principal phases. The first was the pioneer phase, during which the fundamental technologies were developed, initial technical bugs were ironed out, applications were cre- ated (or at least conceived), and bureaucratic and governmental haranguing over the roles of various agencies initiated. This phase was characterized by the development and acceptance of FM transmission, the dominance of military and police usage of radio, and the challenge of building a radio that could withstand the rigors of mobile life. The pio- neer phase lasted until the early 1940s, when the commercial phase began. During the 1940s, radio technology advanced to the point that FM- based car phones were commercially available. Initially, AT&T provided mobile telephone service under the umbrella of its nationwide monopoly. In 1949, however, the Justice Department filed suit against AT&T, set- tling the case with the Consent Decree of 1956. Under this Consent Decree, AT&T kept its telephone monopoly, but was forced to give up a number of other lines of business, including the manufacture of mobile radiotelephones. This allowed companies like Motorola to enter the fray and paved the way for the creation of radio common carriers, or RCCs, much to AT&T's chagrin. These RCCs were typically small businesses that offered wireless service to several hundred people in a fixed geo- graphical area. A Touch of Technology Before proceeding further, let's introduce some fundamentals of radio transmission. For radio waves to carry information such as voice, data, music, or images, certain characteristics of the waves are changed or modulated. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given