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Discussion Starter · #1 ·
I have a 25 foot component, and 25 foot RCA audio running from my PC to my TV. I have a cable modem connected to a "tap" output and then a ~30 foot coax running from the "out" port of the tap to my STB. The cables are all running next to each other along the ground. I noticed that the coax is causing a humming noise, and wavy video on the TV when I select the component input. If i disconnect either end of the coax, the humming and noise goes away. Does that mean the coax is not properly shielded, or perhaps the component or RCA? Is there anything I can do?
 

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This is a common problem. It means that the reference ground from your cable company is not the same as the one from the power lines. Assuming your power lines are properly grounded according to code, you should get your cable company to fix their stuff.


In the meantime, a ground loop isolator will do. Better shielding won't help. (ground isolators are basically the opposite of cable shields -- a high-pass filter rather than a low-pass one. you can make your own by hooking two transformer baluns back-to-back.)
 

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Discussion Starter · #5 ·
I just read about ground loops on Wikipedia, and read that you can use a surge protector with coax inputs. Luckily, my UPS has coax inputs, so I ran the offending coax cable thru it, and now the interference is gone!



I still wish I understood what was happening (and where the difference in voltage is)...


One more question.... let me explain how everything is connected now. Also the cable installer mentioned how the signal in this building (condos) was way too strong, so he put some splitters in to cut the signal. I think he said it was coming in at like 20 db and that could damage equipment (is that true? and is a tap the same as a splitter?)


Brighthouse outside -> 1 way tap ->(tap port) long coax -> 1 way tap... from here, the tap port is connected to the cable modem, the out port goes to my UPS, which then goes out to my TV.


So now, the interference is gone from my TV when I watch the component input. Since the cable modem is connected before the UPS, could there be some interference or something on the cable modem? I havent had any problems with it.


Thanks for all the info!
 
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