Disclosed is an impedance matching multiplexer for a communication system using a cable network constructed in buildings and an in-building system using the same. The impedance matching multiplexer is directed to solve an in-building problem of mobile communication by coupling a broadcasting signal having dual characteristic impedance and various mobile communication signals and using 75Ω premise transfer line widely distributed to watch a closed circuit television (CCTV) and a 75Ω transfer line for a community antenna television (CATV) installed in the building for the purpose of security. The in-building system using a CATV/CCTV cable network is constructed by coupling mobile communication/broadcasting signals for GSM 900/1800, CDMA, PCS, WCDMA, UMTS, HSDPA, Wibro/Wimax, satellite DMB, etc. having 50Ω characteristic impedance with CATV or CCTV signals, and transceiving signals output from an indoor TV-wall surface-terminal or a CCTV camera port which a subscriber will use using the 75Ω premise transfer line. Therefore, it is possible to provide a smooth communication system having inexpensive construction expenses, preventing the building from being damaged by installation of communication cables in the building, and improving the quality of speech.
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