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Coherent echo modulation and detection (CEMAD) is a broadband modulation and detection scheme for the transmission of binary data. In CEMAD each data bit is transmitted and then enters a signal selection process to be retransmitted or echoed for a period of time with the echoing used to advantage in a multidecision process. The scheme can provide 1) transmitter power savings, compared to, e.g., coherent PSK, 2) in effect, both time and frequency diversity reception, and 3) secure communication. It appears to also have a good signal acquisition capability. The scheme is described, and both analytical and simulation results are presented.