Common mode choke

A cable distribution system with devices for attenuating noise propagating upstream from multiple subscriber sites toward a head end, the noise attenuating devices including distributed cable modem filters, the cable distribution system comprising:

• plural subscriber sites in one of the multiple subscriber sites served by a node of the cable distribution system and plural nodes served by the head end of the cable distribution system;
• each subscriber site including a cable modem obtaining power from an alternate current (AC) main power supply interconnected with the node via a coaxial cable and each of the plural nodes interconnected with the head end via an optical fiber,
• wherein the cable modem comprises:
• a modem transceiver receiving a broadcast signal originating from the cable distribution system and transmitting a signal to one of a television front end and a computer within the subscriber site;
• a switching power supply receiving AC mains power from the AC main power source supply via an electromagnetic interference (EMI) filter;
• and
• digital electronics receiving a switching direct current (DC) power supply output from the switching power supply via an inductive and capacitive (LC) filter for filtering noise at a switching power supply frequency;
• and
• a filtering device for filtering noise at harmonics of the switching power supply frequency, wherein the noise at harmonics is carried by one or both of a coaxial shield and a coaxial center conductor of the coaxial cable,
• wherein filtering devices are used with respective modems at the plural subscriber sites to protect the head end from switching power supply harmonic noise otherwise aggregated by the plural nodes and passed to the head end.