Covers basic principles and techniques of digital data transmission, emphasizing its practical problems and the variety of techniques that can be used in the design of a modem. Examines the nature and structure of different digital signals and the basic mechanisms involved in a detection process. Contains a non-mathematical survey of the properties of voice-frequency channels formed by telephone circuits and HF radio links, and the techniques used or proposed for the transmission of digital data over these channels. Describes principles of the coherent, noncoherent, and incoherent detection of digital signals. Covers matched-filter detection, optimum combination of transmitter and receiver filters, and baseband and modulated-carrier signals.