In a full duplex PCM modem system (figure 2), a method and apparatus is provided for robust measuring of the communications channel (67) in which the digital modem (26) transmitter is silenced (54) during generation of training signal by analog modem (12), with silencing of the digital modem's transmitter eliminating problems associated with echo during channel measurement at the digital modem. The above method thus eliminates echo during channel estimation and removes any dependencies on the performance of the echo canceller normally used. |