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. In order to supply further appliances with mains voltage, the coupling apparatus has an additional appliance connection (7), which is likewise low-pass-filtered by means of inductances (4.3, 4.4).