Upstream interference isolating filter for bidirectional cable system

摘要

The upstream noise in a bidirectional cable system is isolated by a filter, with upstream and downstream bands for the respective signals. This comprises a DC voltage switching element for changing the DC voltage for the cable system cable access unit. There is a switchable notch filter switching ON and OFF in response to the action of the DC switching element, and isolating the upstream noise by attenuating the upstream signals in the upstream band, when the upstream filter is ON. The switching element and notch filter are in parallel to the cable.