How do I filter interference?

Discussion in 'Home Theater Projects' started by BigUncleJohn, Aug 9, 2006.

  1. BigUncleJohn

    BigUncleJohn Auditioning

    Aug 9, 2006
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    Installed a projector in the ceiling -- but was unable to test quality of wiring prior to the drywall going up. Now I have scrolling interference lines running through the projected image because of noise on the lines -- most likely AC interference.

    Any thoughts (other than re-wiring) to improve the signal to noise ratio?
  2. Wayne A. Pflughaupt

    Aug 5, 1999
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    Katy, TX
    Real Name:

    You’ve probably gotten no replies because this is not an interiors or construction question. A better place to post would have been in our Displays Forum. I’m surprised a Moderator hasn’t moved it by now.

    Scrolling horizontal lines is a classic indicator of a ground loop. What is your signal source? Often this problem is caused by an improperly grounded satellite or cable TV feed, so if your system has one of those, that’s the first place to look. Disconnect the antenna feed from the cable box or sat receiver and see if it goes away.

    Wayne A. Pflughaupt
  3. BruceSpielbauer

    BruceSpielbauer Second Unit

    May 27, 2002
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    I agree with Wayne above. The most likely cause of what you are seeing is a Ground loop problem. The cause can be many different things, but it can be tracked down and isolated, and it can be eliminated. The trick is to try to use "process of elimination" to be certain you identify the culprit, and then to treat that culprit at its source.

    One recommended method of doing this -- unplug EVERYTHING. Then, start with just the projector / video display. Fire it up. Determine whethger you see the problem, even if you must look at menus and screen savers and messages about "no input" at this stage. Then, methodically, one-by-one, fire up one item at a time, and check after each new item, and see which stage finally adds the video annoyance you see. Process of elimination. Isolate the problem.

    One of the most common causes of this is Cable TV runs, by the way. But, not always.

    Here are two web sites you should read, carefully. Read them in their entirety. Even if the first parts discuss an audio hum, or an audio buzz, some of the info you need to know is still discussed in those paragraphs.

    There are products you can add to eliminate the problem, but I would not purchase any of them until you know for certain WHICH item or component or outlet or coax connection or electrical ciruit is actually in need of treatment. I would hate to see you spend money and time on any "solution" which turns out to be useless, because it is treating the wrong component.

    Here are the links:

    Hope this helps,


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