Just a note from the author. This book is designed to help a reader understand the principles and applications of radio. It is designed for a reader who has learned about basic electronics, perhaps from a book such as the ARRL's "Understanding Basic Electronics." It assumes a high school level understanding of math and science. In addition to developing the science of radio communcication, sections describe other applications such as, radiolocation (radar) and radionavigation. It is developed following a historical perspective. Unfortunately, the first printing went out with some errors. The changes are noted on www.arrl.org/notes/9558/ I hope you find the book helpful.