You need a ground break where the coax attaches to your TV. You can get them a Rat Shack for a few dollars.
5 responses Add your response
The device (Ground Isolation Transformer) is a band-aid and should be treated as such. If you can use the device with no side effects - great... If you have long cable runs, or connections to multiple devices - keep in mind the shielding on all of the cable past the device is floating and thus an antenna. Problems are usually worse in urban / suburban settings.. Best choice is to figure out whats wrong with your cabling / grounding - may not be the easiest route, but the side effects fixing the problem are usually blacker AV presentation.
My extreme case was with a big screen and CATV, VCR, HD Receiver. With all of the cable running to everywhere (20 Meters inside the house and about 300M outside) there were issues. I was able to get rid of the hum using an isolation device at the CATV, but then I had noise bars, ghosting and every possible kind of video issue one could imagine. Finally fixed when I cleaned all of my grounds in the electrical panel, the building ground on the house, ran 6 guage copper from the house ground point to the HT grounding rod and it all cleared up.
On the advise of a Ham Radio operator and audiophile friend - we totally disconnected the house ground from the AV sustem and only used the ground rod for the antennas - The noise floor of the system dropped significantly. Be aware - this grounding technique is against National Electric Code practices and should be used at your own risk.