Cox Jim Cox 
American Radio Networks [PDF ebook] 
A History

This history of commercial radio networks in the United States provides a wealth of information on broadcasting from the 1920s to the present. It covers the four transcontinental webs that operated during the pre-television Golden Age, plus local and regional hookups, and the developments that have occurred in the decades since, including the impact of television, the rise of the disc jockey, the rise of talk radio and other specialized formats, implications of satellite technology and consolidation of networks and local stations.