Upstream ingress noise blocking filter for cable television system

A plurality of intelligently-controlled frequency-domain filters or ingress noise blockers are disposed in serial connection to coaxial cable at feeder tap locations that connect each household node to the cable. Each filter is operative in the absence of upstream signals from the local node to block ingress energy in the upstream band and is responsive to energy produced by injected upstream signals in the upstream band only from the associated local node to unblock and thus pass information signals into the upstream band. The filter employs as its blocking/unblocking mechanism an active switch whose control signal, as well as power source, is the energy of the injected upstream signal, which may be largely the information-containing signal from the associated local node which is to be gated through to the head end. The switch is able to respond quickly to microvolt level signals. The active switch is preferably a depletion-mode-type field effect transistor (depletion mode FET). The present invention, including the strategic placement of the smart filters and the smart filters themselves, does not require a separate external power supply nor a constant source of phantom power.