An adapter device for transmitting data from a local data-handling unit to a remote data-handling unit via an AC power line includes processing facilities that receive digital data from the local data-handling unit and transform the digital data into ISDN data. The adapter device also includes a burst transceiver circuit (BTC) that converts the ISDN data into low-voltage pseudo-ternary signals on a U interface. A transformer of the adapter device transforms the low-voltage pseudo-ternary signals into high-voltage pseudo-ternary signals and transmits the high-voltage pseudo-ternary signals via the AC power line. Such an adapter device may also be used for receiving the data from the local data-handling unit at the remote data-handling unit.