This book is dedicated to the history of the development of telecommunications and is a continuation of the previously published books of the series "Development of Telecommunications: on the way to the information society": "The history of the telegraph, telephone and radio until the beginning of the 20th century" and "The history of the development of electronics in the 20th century." Five chapters of the book tell about the development in the 20th century of methods of modulation, amplification of signals in the paths of transmitting and receiving devices, signal demodulators and devices for suppressing reception interference. It is considered the creation of antennas designed for operation in different frequency bands, as well as antenna arrays, which are increasingly used in radio systems to increase the speed of message transmission and the efficiency of using the radio frequency spectrum.