The Electric Word: The Rise of Radio (New York: Macmillan, 1928), by Paul Schubert (PDF at americanradiohistory.com)
New Online Books
https://www.americanradiohistory.com/Archive-Bookshelf/History-of-Broadcasting/The-Electric-Word-The-Rise-of-Radio-Schubert-1928.pdf
Free ebooks and useful pdf