The 75 ohm and 300 ohm converters can be purchased at radio shack and even Home Depot (at least are local one had them). The real problem comes from the cable company not properly grounding their system. Our local company, Cablevision, in my opinion did a very sloppy job in the wiring and grounded nothing. Call your cable company and complain.

In the meantime use the converters. Also, do a search on ground loop humming and you will find a number of possible solutions. This is how I got the idea of the 75 ohm/300 ohm converters.

John