Line characteristic equalisation method - uses data frame which includes test sequence decoupled to avoid echo effects with run-in and run-out bits

The invention is a modification of the system as in 2653970 in which information was transmitted in data frames comprising two information blocks separated by a test sequence the three elements being separated by transmission gaps. In order to overcome the problems caused by echoes during the transmission gaps it is now proposed to transmit the information blocks and test sequence without breaks. To provide decoupling against energy echoes between the information blocks and the test sequence (B), the test sequence is provided with a number of leader bits (A) and a number of run-3ut bits (C). The test sequence is used to determine the impulse response of the information transfer channel and to set equlisation filter parameters accordingly.