Two-way cable television system with enhanced signal-to-noise ratio for upstream signals

摘要

A cable television system having a bidirectional, downstream and upstream, signal transmission network capable of providing downstream signal paths between a central station and each of a plurality of subscriber terminals simultaneously with upstream signal paths between each of the subscriber terminals and the central station, utilizes controllable signal gates in series with the upstream paths. Each gate is associated with one or more of the subscriber terminals and a portion of the upstream network common thereto. Each gate is activated at appropriate times to allow transmission of upstream signals from the subscriber terminals to the central station; and at other times, to isolate both the subscriber terminals and the common network portion from the remainder of the system's upstream network and the central station without affecting the transmission of downstream signals to the subscriber terminals. The system operates for providing a reduction in the level of undesired noise which normally accompanies desired upstream signals to the central station by reducing the number of noise contributing sources in the system's upstream network. Certain subscriber terminals and portions of the upstream network which are not, at the time, active in upstream signal transmission are removed from the upstream network. Activation of the gates can be controlled by the presence of an actual upstream signal at each gate or by other types of either downstream or upstream signals which are indicative of, or referenced to, time periods during which it is desirous to have the gate activated.