Tech - Ground loop problem in video signal.

Hello,

So I set up a Projector for a friend. We put it in hes garage and ran cables from the house to the garage. About a 60ft run. Hes running composite cables from hes dual dish network receiver in the house to the garage. Thats where the issue comes into play. Its created a ground loop because the satalite receiver is in the house and the projector is in the garage.

I have found a bunch of ground loop isolation devices online to fix such issue. But at the price for these things I am not just going to buy one and hope it fixes the problem. I came here for advise on weather these devices actually will fix my problem. And also any ideas on ways to fix it other than said device.

The ground loop is causing a small horizontal wave on the screen. One after the other. By removing the ground on the projector its self that removes the issue. But that's not good on the projector.

Well any ideas would be great.

Thanks,

 

No one has a opinion?

 

A 60ft run shouldn't be an issue. Back in my pre-production days we would sometimes have pulls twice that distance with no ground bars. The only difference was we were running lines and multiple signals through mixers with isolators. I can't see how an isolator would be a bad thing but I'm surprised you have issues from a single source 60 ft pull. It could be that the projector is not capable of handling the signal the dish is putting out but that's an entirely different issue.

 

If the projector is plugged into a different circuit (house circuit breaker), then the ground of the Dish receiver and projector might be causing issues. That is my guess.

I've only dealt with audio ground loops though.

 

It is a different circuit Asu2003. Just not sure how to fix the issue. I can not really plug them both into same circuit without doing extensive electrical work.

 

Try a temporary extension cord to test it on the same circuit. It is (a good) theory until proven.

The reason it is happening is that power is taking the path of least resistance to ground. It just happens to be through the video cable.

The other possibility is if power lines are running parallel with the (unshielded, untwisted makes it more likely) signal cable.

 

From what you describe, isolating the video signal should correct the problem.

I would just plug the projector into a powerbar or extension cord with the grounding prong busted off. Most electronics aren't a realistic electrocution hazard and aren't bonded anyways. Unless this projector has a chrome housing and people are going to be setting drinks on it, it's nothing to worry about.

 

Doing that will probably work, and contrary to the OP assertion, having power go through the ground isn't really good either.

It still isn't the best if there are any power surges.

 

I will try it with a extension cord ASU2003. Right now it is hooked up with the ground cliped off. Hooked to a surge protector. But I do not like the ground being removed.

 

So, did it work?

I wonder if you plug an un-grounded plug into a GFCI outlet, would it still be protected? It probably wouldn't from surges coming in over the video cable however.

 

ASU2003. This setup is at my uncles. And works been crazy so far to start this week so I have not got a chance to try it. Also I have been building some speakers for the garage to. Which is taking alot of my time. Trying to get the speakers ready for a party in about a week.

 

OK. I thought it was where you were at.

I have built some speakers before. I like screws and construction adhesive. It helps when you make weird shapes.

 

These are just rectangle boxes. But I am putting some aluminum trim on the front around all the speakers. Never built any speakers so this is a learning process. Each one is going to have 2 10" subs a 5" mid and a 3" tweeter.

 

Well I got the front right and left speaker built. They look great. And sound good on DVD and music. But when I put on the TV signal coming from the house I get a noticeable hum. Pretty sure this is the ground loop issue. But with my old speakers which were junk you couldn't tell. So the problem seems to expand into the sound to. I forgot to take 100' worth of extenion cords with me so I was unable to check that.

 

They do sell ground loop (optical) isolators (little cylinders with two sets of audio RCA cables) at Radio Shack or Parts Express. It is another option that is available for audio hum.

 

I bought one of these:

http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=120784912482&ssPageName=ADME:L:OC:US:1123

Not sure if it will help or not. I am unsure at which end I should be putting this? On the satalite box or on the projector/sound system end?

 

Are you sure you have a ground loop or are you just picking up line noise in your cables somewhere in the run? In runs over 25' I like to use coax with RCA adapters at each end. Coax is much better shielded and picks up less noise. The hum in the speakers is probably a 60Hz buzz picked up by either the the audio interconnects or speaker wires running too near a power cable. If audio and power need to run next to each other, make them cross each other at a 90 degree angle and it will cancel the 60Hz buzz.

 

Coax is definitely the way to go for video cables of any length, and I prefer it for audio runs over a few feet. At work I use Belden 1694a with Canare RCAP plugs, they're pricey but entirely worth it in my experience; I've run video 75-100 feet with no noticeable quality loss. For the power, I would make my own cable with grounded shielding and lift ground at the projector end of the cable and an RF choke at each end.

 

Be careful plugging that into a sound system. That is rated at 120V * 6A = 720W. A few sound systems can exceed that.

I would try the satellite box first, since that is what is causing the problem.

On a side note, my amplifier low bass filter was causing my last audio ground loop for some reason. Have you tried plugging in an iPod/computer or something right into the audio sound system to see if the noise is still there?

 

Well I had my computer hooked to it. And the hum was there. But it went away when I pluged the computer in via a 3 to 2 prong adapter. Any time I hook the ground from the garage up to the audio or video I get giant waves in the screen and a loud hum. Right now Everything is isolated from the ground in the garage. The garage and the house are all hooked to the same service coming from the road.

On a side note. Built a center speakers and it sounds great. Just gotta finish the paint and alum. for the front.