DATA COMMUNICATION SYSTEM WITH INCREASED EFFECTIVE BANDWIDTH

A broadband data communication system provides effective increased bandwidth for the transmission of electrical information signals in the system. The signal transmission medium is a coxial cable having main receive and transmit branches, and having drop line pairs connected to the main branches at junction points. A plurality of user devices is connected to each drop line pair, including a particular set connected to a particular pair. Each user device of the set can transmit and receive signals of local frequencies in a selected bandwidth. Frequency isolation means, is connected to the particular drop line pair adjacent its junction point, and passes signals of the local frequencies only from the transmit drop line to the receive drop line, while blocking signals of the local frequencies from transmission over the main cable branches. The particular set of user devices and the filter isolation means together define a subnet. Other subnets can use the same bandwidth of local frequencies without interference, thereby increasing the effective bandwidth of the system. For communication between subnets, a master unit is provided in a subnet which can receive and transmit both at the local frequencies and at master frequencies outside the selected bandwidth; the frequency isolation means passes the master frequencies. The master translates communications from the subnet devices, at local frequencies, into master frequencies for transmission out of tile subnet, and receives communications from outside the subnet at master frequencies for translation to local frequencies and transmission to the user devices of the subnet.