Hum when cablevision is plugged in to tv

Ncarv I tried your suggestion and it worked! Thanks again for everyones help.

Glad to hear it, Romad.

This approach works to block the DC offset but it does not eliminate it. Get the cable company to fix the ground.

Kal

It is best to use the simple solution of isolation with two cheap 75 ohm to 300 ohm transformers of the capacitor -- not transformer -- type back to back. You can chech this with an ohm meter. There should be infinite ohms between the 300 ohm side and the coax side. If your house wiring is connected to the cable TV company's ground and not hardwired directly to your power service ground, you have set up alternate paths for lightning all through your house ( besides the hum problem ). Lightning will seek the path of least resistance. Then if the cable company's ground is better than your own service entrance ground, lightning will go all through your hose and out the cable to ground.
Don Scott