Having a possible ground loop problem... Cable TV (HD)?

Question

I'm almost sure I have a ground loop issue on my cable setup.

For years we had a regular Motorolla digital cable box, and for a year now hooked up to our Samsung HP-S5053 plasma TV, with no problems. After Christmas, we descided to exchange our digital cable box for an HD box so we could watch the local HD channels and some of the paid.

Our first box, made by Pace had faint scrolling lines that would either move up the screen or down it. The cable guy came out and checked resistance on our lines and replaced one of the fittings on the coaxial line hooked into our wall plate. This helped some, but we still had lines and he recommended we turn in the Pace box for Motorolla. We did that and still have lines.

The lines are like window blinds in shape, in a light to regular gradient pattern. Sometimes they blend in so well you can't see them, but on the darker greens, grays, blues and purples, they show up more. Ghost Hunters when they go to black and white low light cameras makes it show up fairly well. In all cases they are faint, yet annoying. I can't see them on HD channels or video on demand, only on SD stuff.

The cable guy came out a second time and is convinced it's a power issue or grounding. Before I bought a ground loop isolater, I wanted to toss it past you guys to see if this sounds like ground looping.

I unplugged our sound system (left it hooked into the system, just no power) last night and still had the lines. The cable box and the tv are on the same power strip. I even tried running the coax feed from the wall through the coax hookups on the power strip before it gets to the cable box, no dice.

We didn't ever notice this problem with our digital cable box, only these new ones. However, the lines do show up some (not as bad) if you plug just the cable line directly into the TV. Everything I've read about ground loop horizontal lines sounds like what we have, but I'm not 100% sure. Any thoughts are greatly appreciated.

BTW: We are using composite cables (red, green, blue) for the video feed from the cable box to the TV. We have optical cables on the cable box and our DVD player.

One other note, I'm not sure if we're just not seeing them, but some channels don't appear to have the lines or as bad. But, it does show up on the full range of channels 2-69.

Answer 1

Check where the cable line enters the house and make sure it's grounded to cold water, electrical ground, or a ground rod.  Also, make sure your splitters are grounded.  Also, you may want to check the signal strength on the line (may be too high/low).  The cable company can do this or call and ask how to pull up the dianostics on that box.  You need to make sure your s/n ratio is good and signal levels are in range.  Also, make sure the line going to the box is rg6 and not rg59.  6 is about 1/4 inch thick and 59 is the flimsy stuck like radio shack sells.  Speaking of radio shack, make sure the splitters are from the cable company and not self bought.  Rarely are the ones from the store any good (don't let the price fool you).  The last thing to check is the quality of the line off the pole.  The 2 guys who came out should have got their ladders out to check for squirrel chews, but rarely do they.  Even if yours doesn't, outside interferance can occur if your neighbors does.

Answer 2

I had same problem and just switched my scart i/o around and this solved it.

May not work for you since you have HD hooked up

Answer 3

I don't have a real answer, but this does sound like UHF interference.  Any high power UHF antenna's in the area?  If so you may want to discuss how to isolate your home's ground from there's.

You could test this by using OTA (Over The Air) equipment in the  2-50 range and see if the artifacts move with it, or dissappear.  

If they disappear, then it's the cable signal.  If not, then I'd look at ground problems in the home.