Abstract: A coupling apparatus (1) having a mains connection (2) for connection to a low-voltage mains power supply system, and having an appliance connection (3) for connection of any appliance for transmitting and/or receiving an RF signal has a voltage converter (5) and a high-pass filter (6.1, 6.2). The voltage converter converts the mains voltage which is present at the mains connection to a very-low voltage, which is suitable for supplying the appliance connected to the appliance connection. Inductances (4.3 to 4.6) of suitable size are interposed in the appropriate connecting lines as low-pass filters for decoupling the RF signal path from the supply signal path, and for suppressing undesirable, radio-frequency signal components in the supply voltages. RF signals which are transmitted or are to be transmitted via the low-voltage mains power supply system are coupled from the mains connection via the high-pass filter to the appliance connection, and from the appliance connection to the mains connection.

Abstract: A PC (10) connected to a low-voltage electricity supply system (9) via a mains plug (11) and a mains socket outlet (12), into which the said plug is plugged, exchanges messages with other apparatuses via the said electricity supply system by means of signals whose frequency is between 1 MHz and 40 MHz. In order to suppress high-frequency interference signals which are generated by further apparatuses which are connected to the low-voltage electricity supply system (9) via mains plugs (11′) and further mains socket outlets (12′), arranged in local proximity to the said mains socket outlet (12), or which are produced by reflections of signals at open line ends, an adapter (1) is in each case interposed there, which adapter is plugged into the mains socket outlet (12′) and into which adapter the mains plug (11′) of the respective apparatus is plugged.