Patent ID: 6973670

Claim:
An in-building CATV system connected to a lead-in wire of an external bi-directional CATV system for transmitting a downward signal inputted from the lead-in wire to plural terminals in a building, comprising: an up-converter for frequency-converting an original upward signal outputted from a subscriber terminal device to an in-building upward signal having a frequency higher than that of the downward signal and for transmitting the in-building upward signal toward the lead-in wire from each terminal via a transmission line; a down-converter provided between the transmission line and the lead-in wire for frequency-converting the in-building upward signal to an upward signal with a frequency lower than that of the downward signal for outputting to the external bi-directional CATV system and for transmitting a frequency-converted upward signal to the external bi-directional CATV system via the lead-in wire; and a noise removal means provided on a transmission path of the in-building upward signal from the up-converter to the down-converter for removing a high frequency signal with a specific frequency used in the up-converter for frequency-converting the original upward signal outputted from the subscriber terminal device to the in-building upward signal; wherein the noise removal means comprises a trap circuit; a frequency of the high frequency signal for frequency-conversion is set to a frequency higher than that of the in-building upward signal; the trap circuit is provided in at least one of the transmission device the up-converter and the down-converter, the transmission device is provided on a transmission path from the down-converter to each terminal; and the trap circuit is constituted by connecting a resonance circuit to the transmission path of the in-building upward signal via an inductive reactance.