Conventionally, digital broadcasting for mobile devices (mobile broadcasting) by using a satellite has been in practical use. In the mobile broadcasting, retransmission of broadcast radio waves is performed so that broadcast radio waves from a satellite can be received in areas where the broadcast radio waves do not reach (such as areas hidden by buildings, underground malls, inside of tunnels, and so on).
Such retransmission system for broadcast radio waves is known as a so-called gap filler device, and is generally configured as follows. The retransmission system firstly receives broadcast radio waves, transmitted from a satellite, by a receiving antenna, and generates broadcast signals for retransmission by amplifying the received signals by an amplifying device and the like and converting frequencies of the signals by a downconverter and the like. Then, the retransmission system transmits the generated broadcast signals to transmitting amplifiers, disposed in areas where the broadcast radio waves do not reach, so as to make the transmitting amplifiers amplify the broadcast signals and to input the amplified broadcast signals into transmitting antennas. Consequently, the broadcast radio waves are retransmitted from the transmitting antennas.
Moreover, this type of retransmission system is usually provided with a monitor device which monitors the operational status of the system by detecting an input level of broadcast signals into the transmitting amplifiers, an output level of broadcast signals from the transmitting amplifiers to the transmitting antennas, and so on. The monitor device is adopted so as to automatically report an error to an external monitoring center when the monitor device detects an error in the system (for example, see Patent Documents 1, 2).    Patent Document 1: Unexamined Japanese Patent Publication No. 2003-332964    Patent Document 2: Unexamined Japanese Patent Publication No. 2004-248078