TWO-WIRE TYPE FULL DUPLEX MODEM WITH ECHO CANCELLER

PURPOSE:To surely decide double talk state by increasing or decreasing sequentially the power of a transmission signal by an output of a monitoring circuit monitoring whether or not a power level of an error signal obtained from a deciding circuit deciding the reception data is a certain level or above. CONSTITUTION:A monitoring circuit 7 outputs a signal when a power level of an error signal obtained from a deciding circuit 6 deciding a reception data and supplies it to a power control circuit 2 as a control signal. The power control circuit 2 gives a difference to correct the difference of the loss conversely even when the loss of the subscriber line at the outgoing side and the incoming side differs between the power of the transmission signals of two sets of MODEMs at the outgoing side and incoming side, thereby increasing or decreasing the power of transmission signal sequentially. Thus, even when a network echo canceller 4 does not have a reception function of a disable tone, the decision of double talk state is ensured.