[mythtv-users] splitting and grounding coax?

Steven Adeff adeffs.mythtv at gmail.com
Sat Mar 31 20:14:34 UTC 2007

On 3/30/07, David Brodbeck <gull at gull.us> wrote:
> Shane Hickey wrote:
> > When I originally cabled it this way, it worked fine, but when I added an external USB hard drive to the setup, I got crazy hum out of my stereo receiver.  I'm sure I created a ground loop somehow.  So, I'm wondering what people use to eliminate that problem?
> You probably have the same problem I had at one of my apartments.  Your
> TV cable and your electrical power system are not grounded at the same
> point.  They're at slightly different voltages, which means whenever you
> connect the two together current will flow.  If that current flows
> through the shield of an audio cable, it will create hum.  If it flows
> through the shield of a video cable, it will create "hum bars," darker
> areas that slowly walk their way up or down the picture.
> You need to break the loop.  Sometimes sketching out the connections
> between various components makes it easier to see where the loop is
> happening.  Unplugging stuff and seeing what makes the hum go away is a
> useful troubleshooting technique.  In my case it was the audio cable
> between my VCR (which was grounded through the TV cable) and my computer
> (which was grounded through its power supply.)  I used an audio ground
> isolator to break the loop.
> If removing the USB drive solves the problem, and it has a three-prong
> plug, solving the problem *might* be as easy as using a three- to
> two-prong "cheater" adapter to break the power ground path for the USB
> drive.  Do *not* connect the ground tab on the adapter to anything.
> (This may be against your local electrical code.  The chances of getting
> caught at it are exceedingly small, though. ;) )

Or ground your splitter to the center screw on a wall outlet.

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