Patent ID: 8040235

Claim:
A relay apparatus for relaying a communication signal transmitted from a power line communication device, the relay apparatus comprising: a first terminal for connecting with a wire transmission line, the wire transmission line for being commonly used as a transmission line of the communication signal transmitted from the power line communication device and of another communication signal transmitted from another device, respective frequency bands of the communication signal and the another signal being different from each other; a second terminal for connecting with the power line communication device; a third terminal for connecting with a power line; a power filter unit including a low pass filter for passing low frequency components, the power filter unit being provided between the second terminal and the third terminal, a first connection line between the second terminal and the third terminal in which the low pass filter is connected between the second terminal and the third terminal and a second connection line between the second terminal and the third terminal in which the low pass filter is disconnected between the second terminal and the third terminal; and a band pass filter, provided between the power filter unit and the first terminal, for blocking the another communication signal transmitted from the another device and passing the communication signal transmitted from the power line communication device, wherein the power filter unit includes a switch unit for selecting between the first connection line and the second connection line, and wherein the switch unit selects the first connection line to cause the impedance characteristic of the power filter unit to be high to prevent the communication signal transmitted from the power line communication device to be relayed between the second terminal and the third terminal while the communication signal is being transmitted between the second terminal and the first terminal and selects the second connection line to cause the impedance characteristic of the power filter unit to be low to enable the communication signal transmitted from the power line communication device to be relayed between the second terminal and the third terminal.