Video Hum Bars


I understand there is a device that can either be bought or made to prevent hum bars from appearing becuase of a ground loop problem with the cable input. Mondial sells this device for around 100.00 (overpriced, I think)-which is a female to female jack that plugs in line with the cable cable- and then I remember someone in Audiogon had disribed taking to transformers and making your own device.

Any thoughts on how to make this unit?

You need a ground break where the coax attaches to your TV. You can get them a Rat Shack for a few dollars.
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.
Thank Rwwear and J k I will follow both of your advise. I will spend a couple of bucks and see what the Shack as to offer..and I will check my cable runs....I do live in the 'burbs.
The reason this happens is that you have too many paths to ground usually. It doesn't always cause problems but it sometimes does. In most cases, and I've seen many, breaking the ground on the TV cable input fixes the problem with no side effects.
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.